An Introduction to Watercolour Mediums

If you thought watercolour painting was just a very traditional, relatively formulaic painting process, think again. Today the possibilities with watercolour are vast, and many watercolour painters are experimenting with the ways that watercolour can be manipulated through the use of mediums, as well as exploring how watercolour surfaces can be altered, or how the finish of a watercolour painting can be modified to enhance the aesthetic you were hoping for. In this section I will give a quick overview of what mediums for watercolour we offer at Jackson’s Art Supplies.

Gum Arabic

Gum Arabic is used to bind pigment in watercolour manufacturing processes, as is made of hardened sap extracted from 2 species of the Acacia tree. It is sometimes known as chaar gund, char goond or meska. Gum Arabic dissolves very easily in water, and is used as the binder in watercolour because it also effectively binds the pigment to the paper surface once the water has evaporated. Gum Arabic allows for more precise control over watercolour washes as it limits the amount of flow and/or bleed of the colour. Gum Arabic also allows the evaporation rate of water, which means that it keeps your watercolour wet for longer, allowing for longer working times. Once water has evaporated from watercolour, the colour’s luminosity and transparency, as well as permanence, is enhanced by the gum Arabic. Gum Arabic is sold separately for those who wish to try making their own watercolour paints by combining it with dry pigment, and it can also be used as a medium to mix in with pre-made colour, to further optimise transparency, luminosity and lightfastness.

Other uses for Gum Arabic

As well as in watercolour, gum Arabic is sometimes used in lithography, and can also be used to transfer images from photocopies, photos or magazines (you can also transfer images using acrylic mediums). Simply sponge the gum Arabic on to the image, and then roll oil based ink over the photocopy. Ink can then be easily removed from the white areas by carefully wiping with a damp sponge.

Jackson’s Art Supplies sells gum Arabic as manufactured by Schmincke, Jackson's, Daler Rowney and Winsor and Newton.

Sennelier Watercolour Binding Medium

Sennelier watercolour binding medium replicates the recipe used by Sennelier in the manufacture of their own range of watercolour paint. It is made of Gum Arabic, honey, water and a preservative. This recipe optimises gloss and luminosity of colour as well as providing a lustrous consistency and a stable structure that will optimise the permanence and stability of the paint structure. Sennelier binding medium can also be used as a flow aid or thinning medium during the painting process with ready made colour, optimising transparency and colour brilliance.

Masking Fluid

Here is a Guide to Applying Masking Fluid on the Jackson's Art Blog.

Watch our How to Apply Masking Fluid video on YouTube

In watercolour painting, unlike other media, the whites are not added as paint but are reserved areas of the paper that are not painted on, so the white is the colour of the paper.Masking fluid is a liquid latex-based product that is very effective at keeping small areas and thin lines white when painting on watercolour paper. The rubber prevents the paint from reaching the paper and is peeled off to expose the white paper left untouched.

The masking fluid can be applied in many ways, almost any tool will work. You may use a brush, a ruling pen, a dental pick, a Colourshaper applicator or a special Masquepen or Super Nib which is a needle that gives extremely fine lines. (The Super Nib comes with an empty bottle that is for filling with water, attaching the needle to the end and squirting the water through the needle tip to clean it when finished. Do this straight away or the needle will be very difficult to clean.) If you need splattered white dots you can flick the masking fluid from an old toothbrush.

If using a brush you might want to keep one inexpensive brush to use exclusively for masking fluid because the latex might not come out completely when you are finished. One trick to make it easier to clean your brush is to wet the brush thoroughly and wipe the hairs over a bar of soap or dip it into washing up liquid, making sure that the hairs are thoroughly coated right up to the ferrule and then use it to apply the masking fluid. Wash the brush thoroughly immediately after use.

Masking fluids come in different tints so you can see where you have painted it. The places that masking are most useful are small white areas or lines within a large even wash of colour, like sailboat rigging against the sky, where you don’t want to paint around areas and interrupt a smooth wash.

The paper must be dry when you apply the masking fluid. If it is wet the masking fluid will soak deeply into the paper rather than sitting on the surface. The paper will usually tear off with the masking fluid when you attempt to remove it when you are finished. The same problem occurs if you dilute the masking fluid when you use it. Shaking the bottle will introduce air bubbles and if applied the bubbles will pop during drying and leave unprotected spotty areas.

Wait until the masking fluid is completely dry, at least five minutes, before you paint the watercolour. After you have finished your painting and it is completely dry you can then remove the masking fluid. Some artists rub with their finger or a putty rubber to get it started. The artist Kory Fluckiger shows in his book Watercolour for the First Time how he paints a patch of masking fluid the size of a penny on a corner of his palette when he starts painting and later when it is dry he rubs it into a little stump and uses this, as the masking fluid sticks best to itself. Get a corner to pull away and then lift this away from the paper and it should pull away in thin stretchy strips or sheets.

Remove the masking fluid as soon as possible after the painting is dry. The longer the mask is left on the paper the more likely it will be to adhere and be harder to remove. Also, the colouring in the tinted fluids can stain the paper if left on for a long time.

After you have mastered using masking fluid you will be rewarded with those lovely sparkling whites in your watercolour paintings.

Watercolour Surface Preparation

Schmincke Aqua Primer

Schmincke Aqua Primer is absorbent enough to enable watercolour paint to adhere to surfaces such as canvas, and wooden painting panels that might normally be used for oil or acrylic painting. 3 layers (that have been allowed to sufficiently dry between each layer) will optimise the absorbency and allow you to achieve the same watercolour effects possible on regular watercolour paper. Schmincke Aqua Primer is available with a coarse or fine tooth. Similar products available at Jackson’s include Daniel Smith’s watercolour ground and Golden Paints’ absorbent ground.

Watercolour Mediums to mix into colour as you work

Granulation Medium

When granulation medium is mixed with watercolour paint it gives it a mottled appearance when the colour would normally appear as a smooth wash. Some colours naturally do have a mottled or granulated appearance, such as French Ultramarine. Granulation medium would serve the purpose of increasing this characteristic in such pigments.

Schmincke Aqua Gloss

Schmincke Aqua gloss remains watersoluble, and can be applied on to dry watercolour to enhance its gloss, or mixed in with wet watercolour as a medium. It also slows the drying time. It is advised not to mix aqua gloss in a watercolour pan as it may affect the paint for future use.

Iridescent Mediums

Aqua Shine and Iridescent medium are both pearlescent watercolour mediums that add a shimmer effect to your colours. They can also be applied to work pure. Both Aqua Shine and Iridescent Medium retard drying and stay watersoluble.

Ox Gall

Ox Gall for watercolour is made of the gall from cows mixed with alcohol. It is a natural wetting agent for the degreasing of undercoats – i.e. it allows for greater adhesion on to already dried layers of watercolour paint. Ox Gall can also be used in gouache painting. Used sparingly, ox gall can also be used as a watercolour levelling agent.

Winsor and Newton Blending Medium

Winsor and Newton Blending Medium slows the drying time of watercolours which enables a longer amount of time for blending. Winsor and Newton Blending Medium is therefore particularly useful when painting in a hot climate.

For Experimental Watercolour Techniques

Schmincke Aqua Collage

Schmincke Aqua Collage is formulated for artists who wish to use watercolour in mixed media works. Aqua Collage dries water-resistant. It is an adhesive that can be applied on its own (in which case it will dry clear and invisible) , or it can be tinted with watercolour. You may wish to use it to glue photos or coloured paper to your watercolour paper, and then work over the top once dry. When dry aqua collage can be painted over without resisting the paint in the way that PVA glue might.

Schmincke Aqua Effect Spray

Schmincke’s Aqua Effect Spray is for the very experimental watercolour painter! Spray into wet watercolour work to create what Schmincke refer to as ‘bizarre surface effects’ on watercolour paintings – basically, it causes the pigment to gather up into pools, to create something a little like flocculation, but also a little like a marbling effect – the colour gathers in pools of saturated colour and leaves area of transparent thin layers of less saturated colour – the surface is broken and undulates. It is worth trying it out on a separate piece of paper to fully understand what it does and whether it is what you want to use on your work. Because Schmincke Aqua Effect spray is in a pump spray bottle, be sure to mask off any areas that you do not wish to apply the effect to.

Schmincke Aqua Pasto

Aqua Pasto watercolour medium is manufactured by both Schmincke and Winsor and Newton. I see Aqua Pasto bridging the gap between watercolour painting and the kinds of impasto techniques you’d be more familiar with in oils or acrylics, and it really does open up the possibilities with watercolour. This is a transparent thickening medium which can be applied pure on to paper, or mixed with colour prior to application, and allows a paste-like texture. You can even start to apply your watercolour paint with a spatula! Aqua Pasto reduces flow, and increases gloss. It slows the drying time and stays watersoluble, so can be re-worked over time. 


Poster and Watercolour Varnish

Poster and Watercolour varnish is manufactured by Daler Rowney, and provides a glossy surface on to finished and dry watercolour works as well as posters, gouaches and designs.

Schmincke Aqua Fix

Schmincke Aqua Fix is to watercolour what retouching varnish is to oil painting. It is a varnish that can be applied at any stage during the watercolour painting process to protect the work that has already been completed. Once the varnish has been applied the paint underneath cannot be reworked. Aqua Fix can also be applied as a picture varnish on to finished works to help maintain lightfastness and protect the work from other environmental elements that may damage it such as dust or dirt.