To create paintings that stay looking like they did when you finished them, often called permanent paintings, there are some basic principles of oil painting that you may wish to follow. This is the advice the experts give for creating paintings that will last. I have researched which guidelines are the most fundamental and why they keep cropping up.

Following these principles will ensure that you have the best chance of creating a painting that doesn’t crack over time, change colour (darken, yellow, become cloudy, have some colours fade or become transparent), wrinkle as it dries, never dry/stay sticky, have a weak paint film that can easily scratch off or that can react with water to soften and wipe off, or have other structural problems. Using or avoiding certain materials and methods can give you the best chance of making an oil painting with longevity, avoiding premature deterioration.

It isn’t always far in the future that a painting might fail. You might sell a painting for £2,000 and a year later the collector contacts you to say it has warped on the wall because of central heating. Shouldn’t they have the expectation that the painting would remain in good condition for 50 or more years? Do you refund them, or replace it, or try to repair it, or tell them it’s not your fault? Some galleries want to know that you know what you are doing when constructing the whole painting, because they don’t want to have problems with unhappy collectors. If you become super famous, of course, museums will go to great lengths to preserve your work.

But of course, I firmly believe that the art comes first. Your vision and your paint handling are more important than how long the painting lasts without changing. But if you could combine your artistic intention with some good painting practises, then over time your art would stand the best chance of remaining as you intended. If you know what you “should” be doing then at least you can make the choice to do it differently knowing what the consequences might be. And remember, there will be exceptions to any generalisation, and there are so many possible combinations of materials and methods that these are just broad guidelines that might help you to make a conscious choice of the materials you use and consider how you work with them.

Six Principles of Creating Oil Paintings with More Permanence

• A rigid support is usually better than a flexible surface
• Direct painting usually has fewer problems later than painting in layers
• A moderate layer of paint is usually better than a very thin or very thick layer
• Use oil paint that contains fewer ingredients
• Use as little oil medium as possible
• Varnish your dry oil painting

Cradled and uncradled panels and boards of different materials.

A Rigid Support Is Usually Better Than A Flexible Surface

This comes up all the time, the experts recommend painting on a panel or to make your stretched canvas really stiff. The paint on an oil painting becomes less flexible as it ages. The oxidation process creates an increasingly more brittle paint film that is susceptible to cracking. You can give the painting stability by painting on rigid supports (panel, board, and canvas or paper mounted on panel or board, or very stiff stretched canvas). This will help prevent the development of cracks in the ageing oil film that are caused by the cycle of swelling and shrinking of the support in response to changes in humidity and the environment.

There are many types of cracking in oil paintings from different causes. The two biggest factors that cause cracking are humidity and temperature changes. Museums work hard to keep these two environmental factors as consistent as possible. But in normal studio storage conditions, or being transported, or in a gallery, the changes in moisture in the air and temperature are more than you might think. Humidity changes throughout the day and the year. The materials used to make most paintings are hygroscopic, meaning they absorb moisture and then release it when the conditions are drier. This creates a cycling of expansion and contraction that can damage a brittle oil paint film. The structural layers of a painting – the stretcher bars, canvas, size, ground, paint, and varnish layers – all expand and contract at different rates, making them pull at each other. Each layer from the bottom up needs to be more flexible, much like the well-known fat-over-lean principle. You build up from a rigid support to a fatty final paint layer and a flexible final varnish.

The easiest change you can make to prevent cracking from environmental changes is to work on a rigid support. Ideally the support surface (panel, canvas, paper) should be less flexible than the size, ground, paint and varnish layers sitting on it. A rigid support can be a wooden panel, an aluminium panel, a heavy paper board, or a canvas made very stiff with sizing. If you wish to paint on canvas or paper then you can glue it to a rigid support to make it a single composite unit. In fact, canvas glued to a rigid panel with a reversible glue like artist-quality PVA, is the best of all as the panel protects the canvas and if the panel gets cracked or old, the canvas can be relocated to a new panel. Canvas is a great surface and since not all rigid supports are equal, canvas glued to the panel gives you the best of both. (That is why Jackson’s handmade linen panels are made with reversible glue on a rigid panel.)

A cradled panel (with side bracing, like a frame around the back) is best because the bracing prevents damage at the corners where panels are most vulnerable, while also adding warp resistance for thin panels. A rigid support also prevents damage to the painting from the back and from movement when moving the painting from place to place. Not all MDF panels are the same, some may have acidic glues in them so are not the best for permanent oil paintings, so it’s best to check if the glue is pH neutral.

For very large paintings, a panel is impractical and a stretched canvas will have to be used. In this case, polyester or linen canvas is a better choice than cotton. Polyester is the least affected by changes in humidity. If you wish to use stretched canvas for other reasons, like the bounce response, then prepare the canvas well to make it as stiff as possible with size and acrylic ground. Going slack over time is a big problem for stretched canvases, in which case they could use a periodic check-up and have their corners opened up with wedges. Keeping the canvas taut will keep the rigid paint layer more stable.

The support isn’t the only thing to consider. The paint layer, the mediums used and how it was applied, all contribute to the longevity of a painting. I took a few snapshots of cracking on paintings at the National Gallery in London. I noticed that no Titian or Veronese paintings on huge stretched canvases were visibly cracked anywhere, whereas Correggio and Poussin paintings on canvas were consistently cracked. This makes me think it was down to the painting mediums they used or some method, rather than the support. Some of the 500 year old paintings look brand new, bright and fresh. It was quite exciting to see!

A detail of cracking on an oil on canvas by Correggio 1525. Photo by Julie Caves at the National Gallery London.

A detail of cracking on an oil on canvas by Jacopo Bassano 1545. Photo by Julie Caves at the National Gallery London.

Many of the paintings looked freshly painted in bright, fresh colours, with little or no cracking. This is a detail of an oil on canvas by Federico Barocci 1575. Photo by Julie Caves at the National Gallery, London.

Direct Painting Has Fewer Problems Than Painting in Layers

Painting in one sitting, not painting on a previous dry layer of paint, removes all the problems of adhesion of layers and cracking from the expansion/contraction cycle of those layers. In general, the more layers the more likelihood of potential problems. Direct painting, also called alla prima, is the most stable way to paint. If you must paint in layers, then using flexible alkyd mediums is helpful. If you wish to paint in layers, follow the fat-over-lean rule of flexible over inflexible.

Sometimes a new layer won’t stick well to the previous layer and the shrinking and expansion cycle can worsen the bond. If any medium or retouching varnish is used between the layers those will expand a different amount, which causes more problems. I personally love painting in layers, but I experience problems with adhesion that I do not have when I paint all in one go in one session or wet-into-wet over a few days.

A Moderate Layer of Oil Paint Is Better Than A Very Thin or Very Thick Layer

A moderately heavy application of paint is better than a very heavy application that will be more prone to cracking, and can take years to dry. But also a too thin layer could cause problems. Overly diluting your paint with solvent will break down the adhesive qualities of the oil content, so it is best to not add too much. If your paint has the consistency of water as a result of adding solvent, it will be at risk of not adhering to your support and could rub off or flake off over time.

Professional quality oil paints like these – Michael Harding, Williamsburg and Jackson’s – are more likely to be free of fillers, driers and other additives.

Use Oil Paint With The Fewest Ingredients

The idea is to keep the chemistry of the paint as simple as you can. Remember that having lots of different ingredients in your painting will not necessarily help you make a better painting, visually or structurally.

The ideal paint will have only pigment and a drying oil like linseed or walnut oil, combined in the best ratio for each pigment. Unfortunately, a list of all ingredients is not required on tubes of ready-made artist paint. In the past, an artist-quality paint wouldn’t contain fillers to bulk up the paint or keep the oil and pigment mixed, and they wouldn’t contain driers to make all the colours dry at the same time. Those were only in student-quality paints. But now even some artist quality paints contain modifiers. But, if you can use professional-quality paints, they are most likely to have the fewest ingredients.

The best paints will also use very lightfast pigments, except where they occasionally make a special paint that clearly states that it is a genuine non-lightfast rose madder, or the like. Old fashioned non-lightfast pigments (fugitive colours) are not usually used by painters, but are for conservators to repair old paintings using the same materials that were used back then. If you want to make a permanent painting you should avoid these colours. Painters don’t need to use fugitive colours, because lightfast, permanent versions of the old dyes have been created and they are great to use.

Some mediums are shown here. Because of their flexibility, alkyd mediums are a good choice if you need to make your paint flow. Stand linseed oil is the least yellowing of the types of linseed oil. But using as little medium as possible is a good rule of thumb.

Use as Little Medium as Possible

It has been said that you should “apply thick paint, thinly”, that working with paste paint in a thin layer is the best way to use oil paint. A well-made oil paint in a tube is at its ideal pigment-to-binder ratio, called the Pigment Volume Concentration (PVC). Adding medium, oil or solvent changes this best ratio, because adding anything will reduce the amount of pigment in relation to everything else. The oil binders in oil paint will yellow over time, some oils more than others, but the strongest, most long-lasting (linseed oil) will yellow the most, because it’s the number of strong molecular bonds that causes the yellowing, so strength equals yellowing. But in well-made oil paint the yellowing is generally not very noticeable because it is masked by the pigment load. So yellowing isn’t a big concern unless you change the pigment concentration by adding anything which will dilute the concentration of pigment, allowing the yellowing to become noticeable. If what you add to dilute the pigment is more oil binder then it is even worse, because it also yellows. The yellowing of the oil binder is most noticeable in whites and blues, so it makes sense to use those colours bound with a less yellowing but weaker oil like poppy or safflower. Blockx oil colour uses poppy oil for its light colours, Sennelier uses safflower oil, and many brands that use linseed for everything else will offer one titanium white made with safflower.

Adding a large amount of oil can also create three other problems: the painting may take more than five years to become touch-dry and when it takes that long you can get areas of your painting that wrinkle, and the drying surface may also attract dust.

If you are using a medium to make paint flow, use as little as possible. Alkyd mediums add flexibility, so they are a good choice. Solvent reduces the strength of the paint film. If you are looking for a transparent effect for glazing, instead of diluting it a lot, dilute it a little and apply it in a very thin layer to be transparent. But again, use what you need to in order to get the paint to do what you want it to, that is still the most important part of painting.

Mediums that contain soft resins (dammar, mastic, larch venice turpentine, balsams, etc) will make paint weaker and more brittle allowing cracks and flaking and will not harden enough to resist solvents when the varnish is removed. Also, artists usually use these too liberally, which results in yellowing and darkening. A safer alternative is to use a small amount of an alkyd medium.

After all, specialist painting mediums aren’t the key to a great painting. A great painting is usually attributed to the strength of the artist’s idea and the painting’s pictorial considerations (tonal values, contrast at the centre of attention, compositional layout, well-observed drawing, colour coherency, depth of space, brushwork, repetition, rhythm, line and shape, etc.)

You can clearly see in this example that the dry, “thirsty” oil painting looks much more saturated when a varnish is applied, as I did on the right side.

Varnish Your Dry Oil Painting

A final varnish will:
1. protect the dried oil surface from scratches
2. accept the pollutants and dirt of the years and when dirty be removable from the painting so it can be replaced with a new clean layer
3. deepen the saturation of the oil paint that can begin to look drier and chalkier as it dries (I think they sometimes look thirsty)
4. even out the surface sheen or change it to matt, satin or gloss
5. seal the painting from absorbing any more oxygen and becoming overly dried out, which means in effect that you will then slow the ageing process

The best practice is to wait to varnish your oil painting until it is thoroughly dry because if you apply varnish before the paint is fully dry the varnish will meld with the still drying paint and no longer be a separate removable layer. It will also form a hard layer on top of a still changing lower layer and that can result in it cracking or wrinkling as the changing oil paint pushes and pulls on it.

There is some confusion about how long you wait for it to be thoroughly dry. The long-standing rule is that it is safest to wait 6-12 months. Gamblin, the makers of the great varnish Gamvar, believe that the 6-12 month rule is too vague and doesn’t take into account the huge difference between the drying time of a painting made with a paint mixed with a fast-drying medium and applied thinly/lightly (much less than 6 months to dry) and a painting with slow-drying colours or mediums painted thickly (much more than 12 months to dry). They also point out that the 6-12 month recommendation originated before the fantastic synthetic varnishes we have now, like Gamvar which is a Regalrez-based varnish. The old natural resin varnishes were both brittle and needed very strong solvents, unlike the synthetic varnishes today that use the more gentle odourless mineral spirits. Gamvar is an excellent varnish because it is a flexible, synthetic varnish that will not yellow. But there is a current misconception among many oil painters that I have spoken with that it has unusual properties that allow it to be applied when the painting is only touch-dry. This is not true, so I wanted to mention it in particular. Some artists think that if you use Gamvar you can varnish in just one to two weeks, when the painting is just touch-dry because their varnish has a special quality that allows some oxygen through. But all final varnishes let some oxygen through. Gamblin say ‘Gamvar can be applied when the thickest areas of your painting are thoroughly dry and firm’. Gamvar is excellent but it is not magical and cannot be applied any sooner than other similar synthetic varnishes.

Most artists want to varnish sooner than is recommended, they need to sell it or exhibit it and waiting is a frustrating problem. If you apply paint more lightly with a small amount of a fast-drying alkyd medium, you may be able to varnish in as soon as two months. There are a few different ways to test the dryness, these include: pressing your thumbnail into the thickest part, pressing the flat of your thumb in and twisting, and wiping with a solvent to test for colour removal. I generally go by how long it has been, how thickly I painted and what fast or slow drying mediums I used and if I’m not sure I will gently press a nail into a thick area hoping for no mark. If I have an exhibition coming up then I give myself a varnishing deadline as part of the process, so the paintings need to be finished 2 or 3 months before. If I can’t do that then I use a thin spray of retouching varnish now and a final varnish later.

The best varnish to use will:
1. not change in appearance over time (yellow or darken or become cloudy)
2. remain very flexible because as the top layer of the painting structure it should be the most flexible layer of the painting
3. remain removable with a solvent that will not remove the underlying paint.

A final varnish made with a synthetic resin is better than a natural tree sap resin (damar, copal, mastic, etc) because it will not change in appearance, become brittle or become less removable over time. Some varnishes also offer UV protection.

It is best to store the drying painting in a dust-free environment and to clean it well with a damp cloth to remove any dust prior to varnishing.

Sunken, dull areas are often remedied by the practice of ‘oiling out’ but this is not recommended because the oil will darken the whole painting and create a yellow film, especially if stored in the dark. This change can occur in as little as one year and cannot then be corrected. Oiling out can be done without these problems if the areas are coated very thinly, wiped away well and then the area is painted over, but oiling out should not be used as a final surface treatment. A removable final varnish is the best way to give protection and allow future cleaning, unlike an oiled surface which cannot be removed when it eventually yellows. To prevent sunken in areas, if you find certain pigments (notoriously the umbers) become dull then use a bit more oil with those as you paint. If your whole painting has lots of sunken areas, then your oil is probably being sucked into a too absorbent surface, so you may wish to seal your surface so it is less absorbent.

If you feel compelled to oil out some sunken patches before you varnish, instead you can try applying varnish to just those patches before applying the full coat of varnish. So those areas get an extra coat. Or oil them out and then repaint on top.

Retouching varnish is a good varnish if used in a thin layer for some protection during the waiting period before a final varnish can be applied. But it is not a good solution for creating adhesion between dried layers when you are continuing a painting. As oil paint dries it becomes more and more resistant to solvents, it becomes more permanent. But varnish continues to be vulnerable to solvent always. So if varnish is applied between layers, it may cause the paint to become less resistant to solvent, even when the paint is fully dry. This may create a risk of the paint being removed more easily if the final varnish is ever removed in the future.

Conclusion

To make a painting that will last, there are some ideal, best practises.
To prevent future problems it is best to use a rigid surface that has been prepared well. Paint on it with very good paints with few ingredients and add as little as possible to the paint, keep it all as simple and basic as possible. If possible, paint in one sitting, not too thickly nor too thinly. Wait until the painting is dry and varnish it with a flexible varnish. And if you choose to change any of these things then you will be aware of how far to take it and what might happen.

Oil Painting Materials at Jackson’s Art

• The Oil Painting Department
• Oil Paints
• Painting Supports
• Oil Painting Varnishes