A Guide to Grounds

Introduction to Grounds

Size, Primer, Gesso, and Ground

Oil Ground

Absorbent Ground

Clear Ground

Acrylic Dispersion Ground is an All-In-One Product

How Do I Apply a Size or Ground?

Three Ways to Prepare Your Surface for Oil Painting

Can I Add a Tone to the Ground?

Staining Canvas with Acrylics and Flow Release

Grounds for Drawing

Frequently Asked Questions

Further Reading

Glossary

A ground is the surface that your paint comes in contact with. It’s the part that you experience with your brush. You may want it to be hard or soft, smooth or textured, absorbent or non-absorbent, coloured, or white. Your ground affects the way the paint handles, how easily it moves on the surface, and how quickly it dries. 

Many acrylic texture pastes can be used as painting or drawing grounds. This can include fibre paste, modelling paste, and iron oxide. Painting with soft pastels requires a ground with a tooth to pick up and hold the pigment particles. This toothy pastel ground can be applied to paper, canvas, or panels. Surfaces can be purchased with the ground already applied to them. 

For watercolour painting on canvas or panels, an absorbent ground can be used to create an absorbent, paper-like surface. The ground can be painted onto sized or primed canvas and boards.

Grounds are of particular interest to oil painters, for whom there is a wide selection available. This includes ready-prepared acrylic grounds, oil grounds, alkyd grounds, casein grounds (a mixture of oil, alkyd and casein, which is a milk protein paint binder) and more. 

There are also grounds for oil painting which are often made by the artist just before applying, like genuine gesso, chalk ground, half-chalk ground, egg-linseed oil emulsion, and others. The recipes for these can be found in books on traditional oil painting or online. Grounds designed for pastel painting can be applied to a sized canvas for use with oil paint. Some painters like the gritty texture.

Although it is possible to paint on unprimed canvas, paper, or wood, you will find that there are some problems with paint handling. With acrylic paint, the canvas can repel water, so the paint beads up and doesn’t flow. With oil paint, the canvas can soak up oil and produce halos of it around painted areas. It can also leave the oil paint crumbly and under-bound. With either paint, the weave could be more visible or bumpy than you want, or the colour of linen may be too dark; paper can absorb oil or buckle from water because it is too lightweight; wood can absorb paint unevenly in the stripes of the grain. Absorption of water can also cause wood to swell or split. 

There are common treatments for surfaces that make them easier to paint on. By using size to seal the surface, followed by a primer, gesso, or ground, an artist can create a surface that allows for easier, more controlled painting. 

These treatments also help to create a more stable surface. This helps to ensure your artwork remains unchanged for longer. To create a painting that will last, you should be as concerned with the proper preparation of the foundation layers that are perhaps not visible (the support, the size, and the ground) as with the layers that you do see (the paint, mediums, and varnish).

Size, primer, gesso, and ground are terms for the parts of the surface of a painting between the support – canvas, wood, or paper – and the paint. Sizing is the first step in sealing the support. But there is some confusion about the other three terms: primer, gesso, and ground. These are often used interchangeably, and not always correctly. Materials manufacturers are not always consistent with how they name products, which can add to the confusion.

A size is a glue that seals the surface to reduce absorption. The surface sizing on watercolour paper helps the paint sit brightly on the surface, rather than be absorbed into the fibres where it will look dull and washed out. On canvas, size prevents oil paint from coming into contact with the fibres, which would slowly be damaged by the oil. Size is also often a stiffener for canvas, so it will wobble less. 

Wood panels do not need to be sealed from oil for longevity. However, sizing gives a better surface for oil grounds or genuine gesso grounds to sit on. It does so by evening out the absorbency of the wood, which would otherwise have different absorbencies between the grain lines and the wood between them. Sealing the wood also prevents moisture from drawing up colour, acids, glues, etc. from the wood into your gesso.

A size can be made from acrylic polymer, PVA, acrylic and casein, or animal gelatine. Be aware that there are over 50 different types of formulations of PVA (Polyvinyl Acetate) and only a few are of a good enough quality to make permanent paintings. PVA for this purpose should have low acidity, retain flexibility, and have low colour change. Look for pH neutral, sometimes called acid-free, PVA. PVA not made specifically for artists will deteriorate and is to be avoided. We stock canvas that is partially prepared; it is sized with rabbit skin glue and is ready for you to apply an oil ground or another coat of glue if you wish it to be clear coated. You can read more about sizes in 'Rabbit Skin Glue: Preparation, Uses and Alternatives' on Jackson's Art Blog.

A primer acts like a glue that bonds strongly to your surface – better than your paint would – creating a base layer that helps the paint adhere more effectively. In essence, it serves as a middleman, ensuring a durable and lasting surface. If your paint hadn’t adhered well, it could be damaged when cleaned, rubbed, or scratched. It could also flake off after it has dried, or delaminate and come off in pieces when it undergoes a sudden temperature shift (the change from storage in a cool room to sitting in the hot sun waiting to be loaded into a van, for instance). Other issues can occur when it is removed from the stretcher and rolled for storage, or if it gets a sudden knock from being dropped.

An acrylic dispersion ground is often called acrylic gesso or acrylic primer. It can fulfil the role of a size, primer, and ground all in one. This medium seals the surface and sticks to the surface even better than acrylic paint, and it provides a ground to paint on. It can be applied directly to a support without the need for a prior application of size. 

Most ready-prepared stretched canvases are Universal Primed, meaning that they have an acrylic ground so you can paint on them with oil or acrylic paint. There are also primers for particular surfaces, such as the Turner Wood or Glass Primer for acrylic paint. Here, the primer sticks to the glass, and then acrylic paint sticks to the primer. Usually, the acrylic paint would not stick to the glass and would simply peel off.

The verb most used for the activity of preparing surfaces is ‘to prime’. 'I spent the weekend priming panels so now I have enough surfaces for the next six months of painting!' But ‘to gesso’ is also used. 'I have to finish gessoing my canvas today because I need to start painting on it next week.'

The term ‘gesso’ is often used as a universal term for all types of primers and grounds. This is because gesso was the original term. Gesso technically only refers to the traditional mixture of hot animal glue and gypsum or chalk. It is applied in many thin layers to wooden panels while warm. Gesso is pronounced with a soft ‘g’ like gypsy or George, from the Italian for gypsum, a major component. Acrylic primers were created to be similar to traditional gesso. Because of the confusion of so many people calling acrylic primers ‘gesso’, most people differentiate the ‘warm glue’ type of gesso by calling it ‘true gesso’, ‘genuine gesso’, or ‘traditional gesso’. 

Genuine gesso is a hard, chalky surface built up of often more than 15 thin layers. It is sensitive to water and will crack if used on a flexible surface, so it must only be used on rigid substrates. Sometimes a piece of muslin is layered onto one of the early layers to give some added strength to the structure. 

Genuine gesso is very absorbent, so it’s the best choice for painting in egg tempera or encaustic. Unless it states that it is traditional gesso, most things labelled gesso are made with acrylic ground. These are not absorbent enough for egg tempera, encaustic, or other techniques or mediums that require the very absorbent surface of genuine gesso in order to adhere. So be aware that there is some confusion in using the word gesso for these two different things. You can read more in our article 'Rabbit Skin Glue: Preparation, Uses and Alternatives' on Jackson's Art Blog.

Casein Gesso

Sinopia Casein Gesso is very absorbent and is the next best thing to genuine gesso. You use it straight from the jar at room temperature. It is made with milk protein (casein) which is a binder in casein paints. It contains a small amount of linseed oil that has been emulsified so it can be thinned and cleaned up with water. The oil content is minimal – just enough to make the gesso flexible and water insoluble after it has dried and cured. Because of this, Sinopia says that the surface doesn’t need to be sized first to protect it from the oil.

Once the gesso is applied, it dries to the touch in a short amount of time. You can apply the second coat the same day when the first is touch dry, but no more than two coats a day. While the surface is stable enough for one additional layer, the oil content has to cure enough for subsequent layers to be applied. Because the recipe includes a linseed oil emulsion, it will take four or five days for the surface to cure and become water insoluble. If you are working with aqueous wash techniques, which soak the surface with water, you should wait for a complete cure. With less water or with oil techniques, the surface can be painted on after a few days.

Unlike genuine gesso, you are not limited to rigid surfaces. That being said, it should only be applied to smaller canvases and pieces of paper. They should never be rolled after the surface has been painted. 

Oil primer or oil ground is oil paint with added chalk. This gives some absorbency and tooth for the oil paint to grab onto. It must be applied over sizing because applying oil primer is the same as applying oil paint, so the fibres need to be sealed from the oil. A stretched canvas, a canvas panel, or primed canvas by the metre, that has an oil ground will often be labelled as ‘oil primed canvas’. Pots of oil ground may be called oil primer, oil ground, alkyd ground for oil, alkyd primer, or thixotropic oil primer. Thixotropic is the quality of some materials to be thick while they are settled but flow once they are stirred, like jam, motor oil, and alkyd mediums. Alkyd resins are created by modifying polyester resins with fatty acids. These are the same fatty acids from the drying oils that are detrimental to cellulose. This means you still need to size the canvas or paper to create a barrier so it can’t penetrate to the fibres. Alkyd usually dries faster than oil paint, so a fast-drying oil ground is usually made with alkyd. 

A canvas with an oil ground usually appears yellow because of the dark yellowing of the linseed oil content. This doesn’t affect the painting if the entire canvas is covered with paint so that the canvas isn’t bare anywhere. The best practice is to use oil or alkyd grounds on a rigid support to prevent cracking. Conservators generally recommend all oil painting be done on rigid supports, anyway.

Since we are located in the UK where lead is prohibited, we do not stock any lead oil primers. But we thought we would mention that they exist. A lead oil ground uses Lead White pigment instead of Titanium White, which affects the drying time and opacity.

It was previously thought that oil painting on top of acrylic paint, or an acrylic ground, was not the best practice. Artists thought the oil paint would not adhere well. This concern has been pretty much quashed these days, so long as the acrylic is absorbent enough for the oil to penetrate into it sufficiently to physically merge with it. This is the case of all artist quality acrylic grounds, and acrylic paint is quite soft and porous.

Acrylic paint can be used thickly to look similar to oil paint or in a more fluid manner similar to watercolour. If you use acrylics in a staining or washy way, you may find an Absorbent Ground or watercolour ground interesting to work on. It’s a bit like painting liquid paper onto your canvas or panel. It can go on top of a ready-made, universal primed canvas to give it a paper-like surface. 

If you are using it for oil paint, be sure that the surface is well-sealed before applying. Some brands require an acrylic primer/gesso underneath and some don’t, so check the instructions. 

If you wish to see the surface of the canvas, paper, or wood – instead of covering it with a white layer – you can use a clear ground. This could be a few coats of matt medium, rabbit skin glue, or a ‘transparent gesso’ or ‘clear primer’. If you are preparing canvas or paper for oil paint, you will need enough coats to act as both the size and the ground.

Be aware that a few coats of ‘clear gesso' can create a white haze. This occurs from a build-up of the material that was used to give it some tooth, so these are not usually actually clear. One way to reduce this effect is to seal the canvas with something truly clear, like polymer medium. Then, use anything that contains toothy material or matting agents, and only use one of those for the final layer. This means there is less of a cloudy build-up. Also since the canvas is now sealed, the clear part of the clear gesso doesn’t soak in, leaving the matting material more concentrated on the surface.

,Acrylic ground (or acrylic gesso or acrylic primer) can fulfil all of these roles at the same time – it seals, primes, and provides a ground. You can simply apply two or three thin coats, wait two days for it to cure if you are using acrylics and three days for oil painting, and you are ready to paint. 

Some artists choose to apply a size before using acrylic primer to reduce Support Induced Discolouration (SID) – a process where the white ground can develop yellow stains as it draws colour from the canvas, wood, or stretcher bars while still wet. This is mainly a concern for painters working with thin, transparent layers, where even slight discolouration may show through.

Even though it can act as size, primer, and ground, some painters only use acrylic primer for the sizing and priming qualities. Some do not like the ground it provides, finding it too absorbent or toothy. Instead, they might mix some matt medium into the ground before applying it. This helps to reduce absorbency. They may also apply an oil ground on top of the acrylic primer after it’s dry.

If you want a more absorbent surface, you can mix modelling paste, extra whiting, or other chalk/marble dust into the ground before applying it. If you want more tooth, you can mix an acrylic texture paste such as pumice paste in with the acrylic primer/ground. You can also mix in pumice powder. If you have a stretched canvas that is universally primed, there is an acrylic primer on it that has sized the surface. This means that you can add any custom ground on top of the provided priming, to give you the exact surface you want to paint on. Some examples are oil ground, absorbent ground, pastel primer, and many other possibilities.

An acrylic ground is the usual choice for preparing watercolour paper for acrylic paint or oil paint. It will add body to the support so that the amount of paint isn’t heavier than the amount of paper. Two coats are usually enough to seal the paper from the damaging effects of the oil for oil painting. See ‘Everything You Need to Know About Oil Painting Paper’ to learn more about priming paper.

Every brand of acrylic primer has a different formula. Some are better at being sanded smooth, while some are less or more absorbent. Some crack more when applied thickly or dried too quickly, and some are not very flexible and state they are for rigid surfaces only. Some brands make a variety of types, calling their less absorbent version ‘acrylic primer’ and calling their more absorbent version with more whiting (chalk) ‘acrylic gesso’. Michael Harding makes one for oil painters that is non-absorbent. All acrylic primers and grounds can be tinted with a little acrylic paint before applying if desired. Be aware that cheap primers (which we don’t sell) may not adhere very well to the support and may peel off later. 

Just to note: Acrylic Primer is called ‘acrylic’ because it is made of acrylic, not because it is only for use with acrylic paint.

A size is generally brushed on with a wide, flat brush. It can also be scraped on with a squeegee, palette knife, or spatula. Scraping may help to fill the holes of a more loosely woven canvas. The first coat is worked into the fibres a bit. You apply 2-4 coats to seal the support from oil paint, or one to seal it from Support Induced Discolouration (SID). Each coat can be applied as soon as the previous is touch dry.

A ground can be applied with a brush, palette knife, or paint roller. Each coat can be applied as soon as the previous is touch dry.

Acrylic ground differs in thickness, opacity, and grittiness, depending on the manufacturer. It is usually too thick to use neat and should be diluted with a small amount of water (up to 10%) until it is the consistency of heavy cream. Most primers have instructions that tell you it is better to apply three thin coats rather than one thick coat – a very thick coat may crack as it dries.

For oil painting, the first coat is often scrubbed into the weave of the raw canvas in circular motions to be sure that it is well sealed, since it is acting as a size as well as a ground. Then, subsequent coats are applied in alternating directions across the canvas. An acrylic ground can be lightly sanded between layers if you wish it to be particularly smooth. If doing so, take care to wear a dust mask.

On linen, cotton, or paper, you can seal the surface to prevent penetration from oil paint and have a good ground to paint on. Here are three ways to do so:

 

1. Apply a clear size and ground, usually 2 to 4 coats of acrylic medium or rabbit skin glue, which will be your final surface. Takes one day to dry. You might do this if you want the surface to show through, for example, leaving parts of the brown linen visible or preferring to paint on a mid-tone background. The acrylic medium provides a smooth surface that is not very absorbent, so you can wipe back oil paint as part of the painting process. The RSG provides a smooth surface that the paint settles into.

• Suitable if you want to see the surface (e.g., leaving part of the brown linen exposed or working on a mid-tone).
• Provides a smooth, non-absorbent surface, allowing for paint wiping techniques.
• Takes one day to dry.
  
  

2. Apply a clear size to seal the fibres and then an oil ground. Remember, an oil ground is essentially oil paint, so it will take the time of oil paint to dry and will need to cure for a week or two. You would use this surface if you like the feeling of the brush on an oil-primed surface. There is just the right amount of brush drag and it is not as absorbent as acrylic primer, so you may have fewer sunk-in areas where the oil has absorbed out of the paint into the primer. Some artists prefer white as it will reflect back through their transparent colours.

• Ideal if you prefer the feel of a brush on an oil-primed surface, which offers slight brush drag.
• Less absorbent than acrylic primer, reducing the risk of sunken areas where oil is absorbed.
• White oil ground reflects light through transparent colours.
• Requires one to two weeks to cure, as it behaves like oil paint.
  
  

3. Acrylic primer/ground, usually a first coat thinned with 10% water, then two more coats, applied when the previous is touch dry, so all coats can be done in one day. Then wait three days for it to cure, so the oil will bond to it properly. You would use this if you like an absorbent surface and you can’t wait for one to two weeks for an oil ground to cure. You may also prefer the ease of one product that does the job of both sizing and ground, and that is water-mixable.

If you wish to use an acrylic primer but would like the 'faster' feel of oil primer (more slippery, less absorbent, slower drying), then you can wipe linseed oil over the whole surface and wipe it back off, leaving the barest film, and then paint onto this, wet or dry. The absorbency of acrylic primers varies a lot. Michael Harding makes one for oil painters that is non-absorbent.

• Good choice if you prefer an absorbent surface and can’t wait for an oil ground to cure.
• Acts as both sizing and ground in one water-mixable product.
• Needs three days to fully cure for proper oil bonding.
• If a less absorbent, more oil-like surface is desired, a thin wiped-back layer of linseed oil can be applied before painting.
• Absorbency varies – Michael Harding makes a non-absorbent acrylic primer for oil painters.
  
  

If you wish to use genuine gesso for oil painting, you will need to apply it to a rigid panel. You can learn more in 'Rabbit Skin Glue: Preparation, Uses and Alternatives' on Jackson's Art Blog.

Painting on a white canvas can cause you to paint in colours lighter or brighter than you intended, so you then need to adjust your colours after you have more of the white covered and you can see the actual colours better next to each other. This is one of the reasons that many painters prefer a wooden palette. 

To avoid misjudging the colours or values on the white, some artists apply a middle value on the whole canvas before they start. This toning of the canvas also prevents unwanted bits of white canvas showing through your brushwork, and you can leave bits of the tone colour showing for added liveliness. Sometimes a middle value, toned ground is used to allow the painter to only need to add the light colours and the dark colours, leaving the toned part unpainted as the middle value. 

In keeping with the fat-over-lean rule, toning is usually done with a lean mixture, the leanest mixture of the painting. Usually, a thin wash of just a bit of paint in a lot of solvent is wiped over the entire surface with a rag. A warm, middle tone like Burnt Sienna might be used to add warmth to a painting that will be composed of mostly cool colours. Using Burnt Umber would be toning with a more neutral colour. It is traditional to use earth colours because they dry faster than other colours. This means you can usually paint on the canvas the next day. 

Some artists scrape leftover paint off their palettes and use it to tone a ground. However, this doesn’t always dry as fast. This is because it can contain some slow drying colours in it, such as Titanium White. You can also experiment with applying black and coloured acrylic primer/grounds.

If you want to use a staining method with acrylics on raw canvas, there is another way to get around the beading up that you would get with a watery acrylic mixture on raw canvas. Skip both sizing and a ground and instead add a small amount of flow release wetting agent to the paint. This decreases the surface tension and allows it to flow and be absorbed by the raw canvas. Because acrylic doesn’t contain the oil that damages the cellulose fibres, sizing isn’t necessary. Please note that these are concentrates and you will add 20 parts water to create flow release water that you then use with your paints. 

Soak-stain painting is a technique famously used in abstract painting. To learn more, read 'Acrylic Soak-Stain Painting: Preparation and Methods' on Jackson's Art Blog.

Acrylic Ground for Pastel

Golden Acrylic Ground for Pastels is designed to prepare surfaces for pastels, charcoal and other art media where a coarse tooth is desired. It contains finely ground sand (silica) in a pure acrylic emulsion. It can be applied to paper, canvas, wood, or any primed support. This allows almost limitless applications for media typically confined to standard papers.

Preparing Your Own Sanded Papers for Pastels

The following pastel primers allow you to prepare your own sanded substrate for pastel work. These coatings work well applied to watercolour paper (300gsm or heavier). They can also be applied to any surface that can take some water, including mount board or wood panels. You can apply ground with a brush, sponge, or palette knife, and tint with acrylic or watercolour.

-  Colourfix Primer

-  Golden Acrylic Ground for Pastels

-  Golden pastes, gels and gritty paints such as fine or coarse pumice gel and micaceous iron oxide

-  Sinopia Absorbent Chalk Gesso and Silverpoint Ground

-  Acrylic gesso mixed with one of the Derivan Matisse dry powders which include a variety of sands, crushed stones, and powders or with marble dust

-  Clear gesso, tinted with watercolour or applied over a watercolour wash

Acrylic Ground for Silverpoint

Golden Silverpoint/Drawing Ground is a liquid acrylic used for the preparation of supports for drawing media. The ground is designed to support fine detailed lines on a permanent, lightfast, flexible ground. Silverpoint/Drawing Ground is ideal for use with metal styli or other drawing tools. It is formulated with 100% acrylic polymer emulsion, a low viscosity fluid that contains high levels of titanium dioxide. It prepares surfaces to accept marks from a metal stylus.

Golden Silverpoint/Drawing Ground is designed for thin applications only. When applied too thickly, the film may crack upon curing. A single thin coat is sufficient. It can be brush or spray applied to paper, primed canvas, wood, or any surface that will accept a water-based coating. The most common substrate for metal point drawing is heavy weight hot pressed watercolour paper.

Note: lighter weight papers are susceptible to buckling from the moisture in the Silverpoint/Drawing Ground. Some artists may find taping the edges down will help prevent extensive warping.

Grounds & Primers: Popular Questions from Artists

Is there a vegan or vegetarian product that you can use instead of rabbit skin glue, for sizing a canvas before applying gesso?

---

Can you sand acrylic primer and gesso primer?

---

Can you use PVA to size a painting surface?

---

What is the difference between acrylic primer and acrylic gesso primer?

Size, Primer, Gesso and Ground Explained

Underpainting in Oil and Acrylic

Comparing Watercolour Grounds on Canvas

Rabbit Skin Glue: Preparation, Uses and Alternatives

Everything You Need to Know About Oil Painting Paper

The Right Canvas: Choosing Stretcher Bars, Canvas and Priming 

Using Sinopia Chalk Ground and Casein Gesso for Egg Tempera Painting

Lauren Amalia Redding Reviews Sinopia Chalk Ground Casein Gesso for Silverpoint

A

Acrylic Gesso
A primer which dries with a coarser texture (or ‘tooth’) than regular acrylic primer. Acrylic gesso can be sanded down if desired. It is made from a mixture of chalk and pigment (usually Titanium White), bound in a 100% acrylic emulsion binder. It can be used as a ground for both acrylic and oil painting.

Acrylic Painting Block
A stack of paper that has been specially prepared for acrylic painting. It is usually sprayed with acrylic primer and glue-bound on all four sides. A gap in the glue will be found on the corner or part of a side of the block. When the painting is finished and dry, the top sheet can be separated from the block by running a clean palette knife around the underside of the sheet. A block is a lightweight support for acrylic painting that will not buckle during the painting process as the glue binding will keep the sheets taut and flat.

C

Canvas
A woven material that has been painted on for centuries. Usually made of cotton or linen. Can be stretched over stretcher bars, glued onto a board or panel, or used unstretched. Acrylic can be painted on raw canvas, but most artists prime the cloth with a ground. This provides control over the absorbency, texture, and colour of the surface.

Canvas Board
Canvas glued onto a hard board (thin MDF or compressed board). A rigid surface for oil and acrylic painting. Canvas board usually has shear edges (i.e. the canvas does not wrap around to the back, unlike a canvas panel).

Canvas Pad
A pad of unstretched, primed canvas sheets glued at one side ready for oil painting. Also available in blocks glued on four sides.

Canvas Paper
Pads or sheets of paper that are textured and coated to have the appearance and feel of primed canvas. Used instead of canvas for economy and convenience.

Canvas Panel
A piece of board or wooden panel on which a piece of primed canvas has been glued to the front and wrapped around the back.

Canvas Pliers
A tool which helps to stretch canvas tightly around a frame in order to make a surface on which to paint. Canvas is usually fixed to the frame using staples on the reverse of the frame, or tacks on the side of the frame.

Canvas Sheets
Sheets of rectangular or square pieces of primed canvas that can be glued to a board to make a panel, or painted on as they are.

Cotton Duck
A heavy plain woven fabric that is popular for artists' canvas. It is relatively low cost in comparison to linen. Cotton duck is most commonly available in 10oz or 12oz weights.

Crackle Paste
When applied to a rigid support with a thickness of at least 3-4 mm, crackle paste will form cracks as it dries. This gives work an aged appearance. It can also be used for special effects, showing through colours from underneath. It can be applied on its own or mixed with colour. The thicker the application, the deeper the cracks. When dry, oil or acrylic paint can also be applied over the top of the paste.

Curing
The second stage of drying of acrylic paint. Acrylic paints dry when all the water found in the paint has evaporated, leaving the dried paint (pigment mixed into acrylic polymer). As the moisture leaves the paint film, the remaining tiny polymer spheres move closer together. This causes the paint film to contract slightly. The pressure that is created by these spheres pushing against one another pushes the last of the moisture out of the paint film, until the polymer spheres start to deform and make bonds between one another. This results in the paint coalescing and forming a continuous paint film. Curing times will vary across brands. It is worth checking the manufacturer’s information if this is of particular interest.

D

Dry Brush Technique
The application of paint with very little water content in it using a dry brush. This is also known as scumbling. The results can have a powdery appearance.

E

Emulsion
An emulsion is any mixture that doesn’t separate. In art, this can be a cold wax medium or an acrylic polymer (acrylic paint).

F

Flow Release/Flow Medium
Reduces visible brushmarks and increases the fluidity of acrylic paint. The go-to medium if you want to create stains and washes on a porous or non-porous surface. Flow release breaks the surface tension of water. This allows fluid acrylic to spread rather than bead up. Many brands are very concentrated and you just need a drop. They recommend making a bottle of water with diluted flow release to use. Some brands, such as Jackson’s, are already diluted so you use a full amount – so be sure to read the instructions on the label.

G

Gesso
Pronounced with a soft g like 'gypsy' or 'George'. From the Italian for gypsum, a major component. This thick white liquid is primarily used as a ground for painting. It can also be used to build up areas for carving on frames and is used underneath gilding. It can be coloured. Gesso for gilding is often coloured red. You can buy ready-made black 'acrylic gesso'.

Gesso is made with calcium carbonate (also called whiting, chalk, and gypsum) in a binder. It is painted on the canvas, paper or wood surface to create a ground on which to paint. Sometimes white pigment (usually titanium, sometimes zinc) is added to make the gesso very white.

Genuine gesso (also called 'true' gesso) uses animal skin glue (hide glue or rabbit skin glue also called “size”) as the binder. The artist often makes the gesso themself, using a double boiler to melt the glue powder and adding the whiting. Rabbit skin glue is now also available ready-made and just needs to be warmed.

One recipe for traditional gesso: 3 parts size, 1 part chalk (whiting), 1 part pigment powder. It is a rather lengthy, messy, smelly process of soaking, heating in a double boiler and mixing.

Acrylic gesso is more correctly called 'acrylic primer' and should not really be called gesso. It uses an acrylic polymer as the binder for the chalky powder. It is made up of upwards of 14 ingredients. You can also buy ready-made black acrylic primer.

Genuine gesso is less flexible than 'acrylic gesso'. It is usually painted on a non-flexible surface, such as a wood panel, rather than on a stretched canvas. This is so that it will not crack. For paints that need an especially porous surface, like egg tempera, genuine gesso is usually preferred to the acrylic gesso/primer.

Acrylic primer varies a lot in quality. Poor quality products can provide a less absorbent ground than is preferred. Good quality acrylic primer is great for both oil and acrylic painting. It does both steps of the surface preparation in one: it both sizes (seals) the surface, and gives a ground for painting. It can also vary in absorbency. Some products are called 'acrylic gesso' rather than 'acrylic primer' and are more absorbent and chalky. These are particularly suited to applications which require an absorbent surface.

Acrylic primer differs in thickness, opacity and grittiness of surface texture, depending on the manufacturer. It is usually too thick to use straight out of the bucket and should be diluted with water until it is the consistency of heavy cream. Most primers have instructions that advise you to apply three thin coats rather than one thick coat. A very thick coat may crack as it dries. The first coat is often scrubbed into the weave of the raw canvas in circular motions to be sure that it is well sealed. The first coat will soak into the canvas or panel and act as its own sizing (sealer). Then subsequent coats are applied in alternating directions across the canvas. To get a very smooth surface you may wish to sand with sandpaper between coats. Some acrylic gessos are designed to have a harder surface specifically so they may be sanded smooth. These are less flexible so they may crack on a movable surface such as stretched canvas. They should only be used on rigid surfaces.

When oil painting, the oil must never reach the substrate. If it does it will rot the canvas, paper, or wood. Traditionally, oil painters seal the surface with rabbit skin glue and then prime the surface with gesso (glue with chalk). Using these two layers assures that none of the oil will seep through. Some artists who use ready-made stretched canvases will apply an additional layer of acrylic primer to the surface to ensure that it is well-sealed

For painting on paper, you may wish to prime both sides of the paper (one after the other dries) as the paper will curl when it is wetted by the primer. Painting the other side then un-curls it. For oil paint on paper, you may want at least three coats.

Priming your painting surface is part of properly creating a painting. The underlying structure is very important to the longevity of the painting, as well as to its appearance. Primer creates a surface that is sealed just enough to prevent the paint from seeping through to the substrate but is absorbent enough to hold onto the paint. If you were to paint on an unusual surface like a rubber toy, the paint might not adhere properly. But if you prime the surface with acrylic gesso/primer first, then your paint will go on properly and stay on. The primer is stickier than paint and will glue the chalk to your substrate. This creates a better surface to paint on.

While the gesso/primer is wet, it may leach colour up from the substrate and cause discolouration to the whiteness of the gesso. The glues in plywood, the resins in wood panels and in stretcher bars may be water-extractable. Sealing the wood or canvas first with a sealant medium, such as Golden GAC 100, will prevent Support Induced Discoloration (SID). Sealing (sizing) with rabbit skin glue does the same thing if you are using genuine gesso. Then prime as normal.

Some artists use a clear primer so that the substrate shows through underneath the paint. This is usually an acrylic matt medium. This is a thick white liquid that dries clear so you can see the canvas. The texture is very different to gesso. Since it does not have the chalk powder in it, the surface is smooth and not as absorbent.

Be warned that priming can be a messy business. Gesso/acrylic primer dries quickly on brushes and can stain clothes. Be sure to use drop cloths and wash everything as soon as possible.

Many artists use the word gesso as a verb meaning 'to prime'. For example, 'I will be spending the day gessoing canvases in the studio'.

Some artists mix gesso in with their paint as a painting material.

Ground
A term often used to describe a prepared surface ready for oil painting. The word ‘ground’ could refer to anything from a primed piece of canvas to an aluminium sheet. A painting ground is the surface onto which you paint. It can be anything. It is usually on top of a sealant/sizing layer of the surface. To be structurally sound, it should be compatible with both the underlying support and the paint that is going onto it. Just a reminder that an artist concerned with the permanence of their paintings should be as concerned with the proper preparation of the foundation layers of the painting that are perhaps not visible (the support, the size and the ground) as the layers they do see (the paint, mediums and varnish).

The ground will give a suitable surface texture and an opaque colour. This will cover the canvas or panel with white, a tinted ground, or a dark colour.

Acrylic primer (less correctly called acrylic gesso) is an example of a ground that is also a size. It does both jobs, sealing the substrate and providing a good surface on which to paint. Genuine gesso is a painting ground for oil paint and egg tempera in particular, but any paint can be used on it. An oil ground is oil paint that has been painted on top of a sizing over the entire surface. This is to prepare the surface for painting with oil colours. Using an oil primer means you cannot paint on that ground with acrylics as the ground will repel the paint.

Painting with soft pastels requires a ground with a tooth to pick up and hold the pigment particles. This toothy pastel ground can be painted onto paper, canvas or panels. Surfaces can be purchased with the ground already applied to them.

To create an absorbent paper-like surface on canvas or panels for painting with watercolours, Absorbent Ground can be used. It is painted onto sized or primed canvas or panels. It is the ground, not the size, so the substrate must be sealed first.

I

Imprimatura
In Italian, ‘imprimatura’ means ‘the first layer’. In painting, it refers to a thin transparent layer of colour that is laid on to a ground evenly in order to colour it. The layer is thinned with solvent or with a fast-drying medium. It is then left to dry before the actual painting of the picture begins. Many artists will leave patches of the imprimatura layer showing through in their work. It is an alternative preparation to a tinted or coloured ground, where the primer is mixed with a colour prior to application to a support.

L

Lightfastness/Permanence
Refers to the stability of a pigment when exposed to prolonged periods of ultraviolet, which is found in natural sunlight. It is measured using the Blue Wool Scale in the UK and ASTM in America. 

Permanence accounts for the effects of other elements on the stability and appearance of pigments. This includes humidity, light, heat, water, acidity, alkali levels etc. The permanence of a paint will be indicated on the label using a rating system. This is determined by the manufacturer and explained in their colour chart or on their website.

To learn more, read 'Fugitive Pigments: Why Do They Fade, and Does it Matter?' on Jackson's Art Blog.

Linen
A natural fabric made from long threads woven together. Linen is stronger and more elastic than cotton duck. It is usually darker than cotton duck and can be stretched on a frame, glued onto a board or panel, or painted on unstretched. Linen needs to be sized with rabbit skin glue or an acrylic substitute prior to painting with oils. Linens are available in a range of weights (the heavier the weight the tougher the fabric will be) as well as a range of weaves, from fine to coarse. Which you choose will impact the overall look of your painting.

M

Matt
Also spelled ‘matte’. A complete lack of shine on the surface. The opposite of gloss.

Medium
An additive that is mixed with paint to extend the colour or alter some of its properties. Mediums can alter consistency, texture, transparency, drying time, and more.

Monochrome
The use of only one colour in a painting, which is likely to appear in a range of differing tonal values.

Moulding Paste
Moulding (or molding) paste is a white opaque acrylic paste. It is used to build surface layers and create texture on a painting surface. It can be tinted with acrylic colour or applied on its own, left to dry, and then painted afterwards. It dries hard yet flexible.

O

Open Acrylic
Open acrylics are slow-drying acrylic paints. They allow for painting approaches that were previously only possible in oil paint.

Open Time
The length of time in which it is possible for a brush to move applied paint around on a surface before it dries. Also used for the time a gilding size (adhesive) stays sticky for metal leaf application.

P

Palette Knife
Palette Knives are also known as painting knives. They are used by painters to mix colour and apply paint to a support. They are usually made from plastic or forged stainless steel. They are easy to wipe clean with a rag which means it is easy to keep colour mixes clean as well. As a painting tool, it is ideal for impasto technique and also for applying colour in a flat and uniform layer.

Panel
A rigid painting surface. Used for acrylics, oils, encaustic, pastels, and watercolours. Made from solid wood, plywood, MDF, compressed card, or aluminium. They are often braced to prevent warping during the priming and painting period and over time. May also be wood with canvas or paper adhered to the front. Useful for encaustic or oil painting where a rigid surface helps prevent cracking of the paint surface over time.

Paper

Watercolour Papers
Watercolour paper has a ‘hard size’ on top of the paper. The size allows the water to penetrate and the pigment to remain on the surface. This gives the painting its brilliance and also allows for corrections.

Watercolour paper comes in different textures. ‘Hot Press’ (HP) is the smoothest. It is also a bit less absorbent as it has been compressed to a harder surface. ‘Not’ (also called cold pressed) has a medium textured surface and is the most popular finish. It is very good for beginners. ‘Rough’ is highly textured paper and is the most absorbent. Botanical artists often prefer hot pressed paper. This is because the smoothness of the surface allows them to be very precise in their rendering.

The weights of the papers range from 90 lb to 400 lb. The heavier the weight, the less the paper will buckle when wet. For lighter weight papers (140lb and below) the paper is usually stretched. This process involves wetting the paper and laying it out on a board. It is then taped down with gum-strip tape. You can also use a specially designed paper stretcher device, like the Keba Artmate.

Watercolour papers can vary in whiteness. This ranges from bright white to a creamy off-white. They are also available in tinted colours.

Watercolour papers come in sheets, pads, rolls, and blocks. Blocks are pads of pre-stretched paper that are glued on all four sides, except for a small space on one side. This allows for painting without stretching. When the painting is dry, you can remove the top painted sheet by running a butter knife around the edge from the gap in the side.

Drawing Papers
Cartridge paper is a type of heavy paper used for illustration and drawing. It comes in a variety of smooth textures. It is available in loose sheets, pads (gummed or spiral), and hardbound and softbound sketchbooks. It can also be purchased in full-size rolls.

Bristol paper is a strong and durable, all-purpose drawing paper. It has a very hard surface that is heavily sized, polished, and compressed. It is also used for airbrushing.

Other papers that are suitable for drawing include the popular Stonehenge paper.

Pastel Papers
Pastel paper is used for soft and hard pastels. It is also popular for use with charcoal. It is usually coloured paper, with the chosen colour being very important as it will be a major component of the finished work. It comes in a few different textures, all with some amount of tooth or weave that will catch hold of the pastel particles. 

Ingres is a laid paper with a mesh imprint from a screen. The random texture gets its surface from a cloth matt imprint, similar to Not texture watercolour paper. There are a few types with toothy textures, such as ground cork or sand that are similar to sandpaper. A few come with the colour screenprinted on. Some are waterproof for working the pastels with water. Paper for oil pastels is hard and white. It usually comes in a pad with glassine paper interleaving to protect it from smudging.

Oil and Acrylic Painting Papers
These medium to heavyweight papers are usually canvas textured and primed for painting with oil or acrylic. Most of the papers prepared for acrylic paint are universally primed to accept both oil and acrylic. Paper must be sealed completely if painting with oil paints. This is because the oil will separate out if the paper is absorbent and form a halo of oil around the colours. It will also rot the paper over time. Although acrylic paint can be used on any paper, acrylic paper is usually designed to mimic canvas or is very heavyweight. Oil and acrylic painting papers are great for taking to classes or using in the field. They are an economical choice for making a study or sketch prior to the major work on canvas.

You can also get sheets of primed actual canvas (as opposed to the canvas-textured paper) in pads.

Fine Art Digital Papers
Inkjet papers are used to create high quality reproductions of your artwork. These papers come in a wide variety of textures and weights. They are coated to accept inkjet inks. They can also be sprayed with an inkjet fixative to prevent smudging. They are archival. Sheets of primed canvas designed to go through your inkjet printer are also available.

Paste (acrylic)
A thick, white opaque medium that can help to build up texture and impasto marks. It can be tinted with acrylic colour or used on its own. There are many different acrylic pastes available. Each brand offers a variety of consistencies and textures/characteristics.

Permanence
Permanence takes into account all factors that may influence the stability and appearance of pigments. This includes exposure to UV rays, humidity, heat, water, acidity, alkali levels, and more. The permanence of a paint will be shown on the label using a rating system. This is determined by the manufacturer. It will also be explained in the manufacturer’s colour chart or on their website. Some manufacturers say permanence when they mean lightfastness (which only considers UV). It’s worth double-checking if this is of particular concern.

Pigment
Pigments don’t just give paint its colour. They will also alter how the paint behaves as you work. Tinting strength, opacity, granulation and other properties are all a result of the pigments used in a paint. Different brands make even the most familiar colours with varying recipes, so it’s best not to rely on titles alone.

Pigment numbers are grouped into nine categories. Each number is prefixed with a code that indicates its group.

These codes are PR, PO, PY, PG, PB, PV, PBr, PBk and PW. They refer to red, orange, yellow, green, blue, violet, brown, black and white respectively.

Some pigments will crop up again and again across a colour chart. For example, PBr7 represents the natural iron oxide used to produce raw and burnt umbers and siennas. Others will appear in variations, either denoted by a colon or a secondary figure. For example, PW6:1 is Buff Titanium derived from PW6 Titanium White. Other variations may be listed in brackets, such as in PV23 (RS), a Red Shade of the Dioxazine Violet pigment. It can be useful to look at the paints you use most often and make a list of your preferred pigments. This is especially helpful when considering purchasing from new brands.

While there are plenty of good reasons for a manufacturer to mix pigments, painters will often prefer to use colours with one pigment. Single pigment paints are more predictable in mixes and tints. A paint made from multiple pigments might create unexpected combinations on your palette. Still, mixes can be beneficial. They are commonly used in the production of hues. Hues are convenient replacements for dangerous or expensive pigments. They are often the only form in which defunct historical colours can be found.

Plein Air
To paint out of doors in front of the subject. Famous artists who painted en plein air include Pissarro and Renoir.

Primer
Used to coat a support to get it ready for paint application. Acrylic primer is made from calcium carbonate suspended in an acrylic binder. It can be applied directly to a support without the need for a prior application application of size. To create a very smooth surface, apply 2- 3 coats and allow to dry fully, lightly sanding between applications. Gesso is a more absorbent variety of primer. Multiple coats of acrylic gesso will increase the absorbency of the surface, and light sanding between layers will optimise the smoothness.

Acrylic primer varies a lot in quality. Poor quality products can provide a less absorbent ground than is preferred. Good quality acrylic primer, which can contain upwards of 14 ingredients, is great for both oil and acrylic painting. It does both steps of the surface preparation in one: it both sizes (seals) the surface and gives a ground for painting.

Priming Brush
Usually a flat wide brush, made with synthetic or hog hair. For an even application, load the brush and apply whilst holding it at around 45 degrees to the support. Brush the primer on in all directions to make the coverage even. Allow each layer to dry fully before applying the next layer.

R

Rabbit Skin Glue
A strong glue made from animal parts. It is an ingredient in genuine gesso, used for sealing (sizing) panels and canvas before priming. It is also used as sizing for papers. It stiffens canvas in preparation for gesso primer in oil painting. Also called hide glue.

For preparing canvas and panels, the usual method is to soak the pellets or powder overnight. Then, the next day, heat in a double boiler and brush onto the canvas while still warm. Do not overheat as the glue will be weak. Two coats are preferred to seal the canvas well, the first being scrubbed into the canvas to get well into the weave. Discard any left over as it does not reheat well. Then prime the surface as normal.

S

Sinking In (Oil Painting)
When paint is absorbed by the surface it has been applied to. This causes the colours to appear less saturated than when they were first applied. This can cause some areas of the painting to appear more shiny and colour filled than others. 'Sinking in' can occur when there are inconsistencies in the absorbency of a surface, which affects the varying degrees of ‘sinking in’ on a surface.

Stretched/Unstretched Canvas
A piece of linen, hessian, or cotton duck that has been tightly wrapped around a frame made of wood or aluminium and fixed at the back. Sizing and priming the stretched canvas will increase the tension in the stretch. This creates a vibrant, drum-like surface to paint on. Stretched linen and cotton duck canvases can be bought ready-made. They are available unprimed or primed with acrylic or oil primer. Unstretched canvas can be purchased from and by the roll. It is ready to be stretched onto a frame at home or worked on unstretched.

Stretcher Bars
Stretcher bars will assemble to make a frame onto which canvas can be stretched over. They are available in pairs and made of wood or aluminium.

Support
A general term for a surface ready to be painted on. A support can be anything from a canvas to a wood panel.

T

Tacks
Tacks are similar in shape to drawing pins. They are made of metal and are used to fix canvas to the sides of a stretcher bar. Staples are generally considered to be more successful at keeping canvas fixed to the stretcher. However, tacks are often still used to add a traditional aesthetic to the overall look of the support.

Toning a Canvas
Painting on a white canvas can cause you to paint in colours lighter or brighter than you intend. Then you need to adjust after you have more of the white covered. To avoid this, some artists apply a middle value on the whole canvas before they start. This toning of the canvas also prevents unwanted bits of white from showing through your brushwork. You can leave bits of the tone colour showing for added liveliness.

Tooth
Tooth usually refers to how coarse a surface feels when dry. Often used to describe the surface quality of gesso, primer, and acrylic pastes and mediums.

Transparency/Opacity
The measure of how much light is able to pass through an applied paint and interact with the surface beneath. Transparent paints appear more luminous on a white support. This is because they allow a larger proportion of light to hit the surface they’re on, like a filter placed over a light bulb. Opaque paints block this reflection from occurring and can be used to cover layers of colour underneath. Transparent paints are better suited to glazing techniques. That being said, glazing can still be achieved with opaque colours. They should be diluted sufficiently or mixed with a suitable medium.

U

Undertone
The appearance of a paint when it is spread across a surface in a thin film.

Underpainting
The initial layer of painting. It is usually painted in a minimal number of colours. This helps to establish areas of tone and ‘map out’ the composition on the support.

W

Weave
The weave of a canvas can be completely smooth or very prominent, depending on how it was made. It will have an effect on how your painting looks. Artists who like to explore textures in their work might prefer a coarser weave, whereas artists who paint very fine detail may prefer a finer grain. 

The set of threads that are aligned lengthways in fabric is known as the 'warp'. The 'weft' is the set of threads that weave in and out of the warp. In painting, it is important that the warp and weft are similar. This is so that when the canvas is stretched it will do so uniformly, without inconsistencies such as wrinkling. This is particularly worth noting if you are working with linen that was not purchased from an art supplier.

Wedges
Wedges are supplied with ready-made canvases and stretcher bars. They provide a way of making your canvas even more tightly stretched. Simply insert the wedges into the corners of the frame of your stretched canvas and gently tap in with a hammer. The wedges will push the stretcher bars outwards and keep them in place. If the same amount of pressure is put on each wedge then the canvas will remain square. By pushing the bars outwards you will be tightening the tension of the canvas stretched on the other side of the frame.

Whiting
Calcium carbonate or calcium sulfate. Also called chalk, marble dust, calcite, and gypsum, depending on its source, use, purity, and particle size (which affects both the texture (gritty or silky smooth) and the absorbency). Talc is not included in this group. This is because is too soft for use as a painting ground, unless it is used in a blend with one of the above minerals.

It is a white powder ground from fossilised shell deposits (limestone), marble, or made synthetically. It is made synthetically by precipitating fine particles of calcium carbonate. This makes the most uniform, smoothest variety. It is used for the preparation of panels for egg tempera, for example.

Its use for artists is mainly as an ingredient in genuine gesso and acrylic primer.

It is also the opacifier that makes gouache an opaque form of watercolour paint. It is used in some soft and hard pastels. It is used as a filler for some paints. It is used to enhance the brightness of some paint colours, such as Viridian. It is the inert base onto which lake pigments are precipitated. Some forms are used in modelling paste in acrylics. Mixing with oil makes oil painting putty.

Whiting is not strong enough to be used as a white pigment. It is added to paper pulp as a buffer, to counteract reactions with pollution that would cause acidity in paper. It is also used as a polishing powder. In ceramics, it is used as a flux.