An Introduction to Varnishing an Oil Painting
As we’ve discussed in 3 Reasons why artists varnish their work (and why some artists don’t) varnishing is primarily an aesthetic choice on the final finish of your painting.
Not only can it really bring up the vibrancy and richness in your realist paintings but it offers protection for the painted surface from atmospheric effects to make the surface easier to clean in the future.
No One technique for varnishing suits every situation — the texture of the paint surface, whether you want a matte or gloss finish, speed of completion etc.. all effect which varnish you choose.
There are different considerations to think about when you’re working with Oils in comparison to Acrylics, so here are some common questions to check before getting out the varnish brush…
1. How long should I wait before varnishing an Oil Painting?
When you’re varnishing an oil painting it really depends on how thick or thin the paint application is. So if you work in very thin layers it dries a lot quicker than if you work impasto with thicker blobs of paint.
The other thing to consider when using Artist quality paints is which pigment you are painting with – if it’s a quick drying or slow drying pigment.
For example, if you’re using Alizarin crimson or Ivory black which are very slow drying, (there is a lot of oil used in the binding process of the oil paint) it would take a lot longer to dry compared to if you used a fast drying paint such as Raw umber which has a lower oil content in it. Earth colours such as Raw umber dry a lot quicker.
Pro tip: Some brands of student quality oil paints contain driers in their slower drying pigments in order to bring the drying times closer together.
Drying rates tend to average out as colours are almost always mixed on the palette, so the drying times tend to equalise to a great degree.
N.B This is just a reference to traditional oil paints and different drying times of each pigments, I’m not referring to ‘Quick drying oil paints’ that dry within a day.
The Drying or Curing Process
Traditional oil paints dry by oxidization, when the oil reacts with oxygen in the air. There isn’t any water in the paint to evaporate (unlike acrylics which dry by evaporation).
The pigments in oil paints are dispersed in oil, which may itself be dissolved in a solvent and that solvent evaporates away when the paint dries. which can be dissolved in a solvent, this solvent evaporates away when the paint dries.
This leaves the pigment and oil behind.
The oil doesn’t evaporate, the linseed oil and pigments oxidize, meaning they react with oxygen and harden.
Which is why you shouldn’t varnish an oil painting with traditional varnish until it is fully cured as putting varnish on a touch dry painting won’t allow air through the varnish layer and will stop it drying properly and fully.
So how long would it take for a painting to be touch dry on the surface?
If you have very thin paint application with earth colours, an oil painting can be touch dry within a day or two for a thicker painting with other pigments it may take 10 – 14 days.
How long would it take for a painting to be fully cured/dry?
If you have very thin paint application with earth colours, an oil painting can be fully dry within a couple of months but for a thicker painting it may take 6 months or as long as 2 years.
For most artists waiting 6 months or a year to varnish can seem a bit excessive, especially if the piece is for an exhibition or a commission that you can’t easily revisit to varnish at a later date.
There are some modern synthetic varnishes that are now being manufactured that have the benefit of allowing the oxidation process to take place through a permeable varnish layer applied to a touch dry oil painting.
This allows artists to varnish their work after only a few weeks, whoo hoo!!
What is the worse that could happen if you varnished a touch dry but not fully cured painting using a traditional varnish?
The worst that could happen would be that your varnish layer would crack as the paints contracts as it dries, however, this would really only be most apparent if you painted with a very thick application of paint. Also, the oil wouldn’t be able to fully harden so it wouldn’t be a super strong bond between the layers.
It’s always advisable to follow good professional practice for the conservation of your pieces if you’re using traditional varnishes.
2. Do I need to apply an isolation coat with an oil painting?
No, you don’t need to apply an isolation coat to an oil painting.
Once the oil paint is dry enough then you can apply the varnish directly to the painting surface. This is because if you ever needed to remove the varnish at a later date, the solvents used to remove the layer of oil varnish won’t damage the existing oil paint layer.
On an acrylic painting this differs as the isolation coat adds a much needed sheet of thin protection over the paint surface.
3. What’s out there? – Traditional or Synthetic Oil Varnishes
Traditional Natural Varnishes:
Dammar, Copal, Amber, Mastic
Traditional Natural Hard Varnishes
Copal and Amber varnishes, referred to as a hard varnishes, was used by the Old Masters.
They are a lovely Golden colour and as such, give a rich glossy and enamel-like appearance. However, they are susceptible to cracking, extensive yellowing and become increasingly difficult to remove from a painting over time.
Generally they’re harder to come by or they simply do not exist as they are the fossilised remains of prehistoric tree sap and many of them have been mined to extinction.
Hard varnishes do not redissolve in a solvent such as Mineral Spirits or Turpentine. They must be dissolved in hot oil which can get a tad complicated!
True hard Copal and Amber varnishes are rare in the world today, some specialist manufacturers still offer unique historically-accurate painting varnishes if you want to go completely old school.
Traditional Natural Soft Varnishes
Dammar (can be spelt Damar) and Mastic varnishes are referred to as soft varnishes, they dissolve in solvents such as Turpentine and Mineral spirits.
This means soft varnishes are still removable from an oil painting surface without greatly affecting the paint layers below.
Pro-tip: To dilute the Dammar varnish you ideally need to use Turpentine which is better suited to a well ventilated separate studio space, rather than a ventilated room in a home. Odourless Mineral Spirit (OMS) is not strong enough to dissolve the natural resins of Dammar.
Dammar varnish comes from tree resin and is paler than Copal but has great viscosity and is still used commonly in oil painting today, the visual aesthetic look of Dammar has a luscious quality to it similar to the historical hard varnishes.
The issue that can come with Dammar (because it’s a natural resin) it has a tendency to yellow over time and as it dries it becomes more brittle, leaving your canvas more likely to crack if the canvas is knocked.
Pro tip: I often use Dammar in the final layers of an oil painting as part of the glazing medium because it really goes on so nicely and has a nice translucent quality when you first apply it. The advantage of using the Dammar varnish in the final glaze helps to make the medium leaner than if we just used Linseed Oil. It also saturates the colour a lot more than if we just used Turpentine or Mineral Spirits to dilute the paint consistency. Because we mix the Dammar varnish with Linseed Oil in the glaze medium, the flexibility of the Linseed Oil balances out the brittleness of the Dammar varnish.
All that aside, it’s a personal choice as an artist and for some of my paintings I like the idea they will have that lovely soft, warm yellow glow to them in the future.
I use the choice of varnish as an aesthetic judgement, it might not be as technically sound as keeping a crystal clear finish that the synthetic varnish would give but I just like it.
A note to newcomers to Dammar
I usually apply Dammar varnish to smaller paintings as it can go very tacky, very quickly and is harder to control with a brush.
Dammar is most commonly used in liquid form and applied with the brush, however, if you’re after a really super smooth finish it can also be found in aerosol can form and used as a spray application.
This can be very effective to get a smooth finish if you’re not used to applying with a brush. You’ll get more product wastage and you need a really well ventilated space or a very still dry day to work outside, but the results can be very smooth.
New synthetic varnishes:
MSA, Gamvar, Alkyd Synthetic Resins
The synthetic varnishes offer a lot of advantages over the traditional natural varnishes
A clear coat on first application that stays clear over time, therefore non yellowing and more flexible.
They are available in liquid or aerosol form, are readily available and cost-effective and they come in a variety of sheens, such as matte, satin or gloss.
They also allow for relative easy removal with less risk to underlying paint layers.
Alkyd Synthetic Resins such as Schmincke Picture Varnish provides a glossy, non-yellowing, colourless, highly resistant top coat. (most similar to a hard varnish) Must be applied after 8-12 months.
Mineral Spirit Acrylic varnishes (MSA’s) have a high molecular weight tend to offer a better protective surface, have greater elasticity and more resistance to blooming. Must be applied after 8-12 months.
A quicker finish
Some recent varnishes also have the great advantage of being able to be applied when the painting is just touch dry – rather than waiting for the painting to be fully cured.
Gamblin make a varnish called Gamvar which has been developed specifically for this purpose.
It either comes in two parts system or premixed by Gamblin.
You can only brush or sponge apply it, as it is not available in spray form, however, it’s a lot easier to apply than Dammar because it has a longer working time when you’re brushing it on.
Sponge application can also give a smooth finish and enable you to keep your materials super clean by using the sponge once and then throwing it away.
Gamvar saturates and gives greater depth to the colors in your painting and gives your work a unified and protective semi-gloss surface. Developed in collaboration with the National Gallery of Art, Gamvar goes on water-clear, stays water-clear and can be easily and safely removed with Gamsol. Gamvar is virtually odorless and ready to apply.
Gamvar can be applied when the thickest areas of your painting are thoroughly dry and firm to the touch.
The greatest advantage of the Gamvar varnish is the ability to apply it when the painting is touch dry. This is a revelation when varnishing an Oil.
4. What is ‘Sunken in’ and ‘Oiling out’?
Sometimes you can find areas of your painting that have turned dull, matte and lighter in colour, even though surrounding areas are still glossy and rich. This is where the oil from the paint has soaked into an absorbent ground and left just the pigment on the canvas surface. This is referred to as a ‘sunken in’ area.
There are a couple of main reasons why it happens:
1. Too much solvent or Turpentine in the paint mix
2. A cheap Gesso, a too absorbent or an unevenly absorbent ground
The two options you have to restore an uneven sheen to your painting before final picture varnishing are:
1. ‘Oil out’ the surface – this is a method of applying sparingly a thin coat of Linseed oil or clear artist medium over the entire surface of the painting.
The painting must be touch dry and then you can apply the oil with a clean, lint-free rag or paint on with a soft brush and then remove most of it with a rag.
2. Apply a Re-touch varnish – Re-touch varnish is a standard Dammar varnish that has been diluted with Turpentine by the manufacturer.
It can to be used during the course of a painting and as a temporary picture varnish to restore colours and add an even sheen to your painting yet still allow the oil to dry fully.
Also, you can paint over the top of a Re-touch varnish.
To apply it, the painting must be touch dry and I’ve found it is most effective as a spray because you can build up the layers gently, compared to applying with a brush.
If you were to apply the final picture varnish directly on top of your painting without oiling out first, all that will happen is the glossy areas will look more glossy and the matte areas will only look a bit more glossy – so you’ll still have the difference in sheens between the two.
Notice the difference in colour between: Re-touch varnish, refined Linseed oil, Dammar Varnish.
Pro-tip: If the difference in sheens is very minimal then you don’t have to oil out, you can go straight on with the final picture varnish.
5. Will the varnish even out the sheen of my painting ?
If you have a minimal difference between matte and gloss areas, then yes it will.
If you have obvious, larger areas of different sheens then see ‘Oiling out‘ above, as the varnish on its own will only emphasize the differences.
For oil painting, the matting agent that is usually added to the gloss varnish is a wax. You can mix in different quantities of wax to change the sheen of your varnish.
You can also apply Cold Wax Medium straight to your painting and then buff it up with a rag and this will give you a very slight lustre to your finished work.
This can be easier to apply than using a brush with Dammar or Synthetic varnishes as the product is in a wax form – similar to adding wax polish to a table.
However, for realist paintings when you are trying to bring out colours and form in your work, the matte varnish will dull, desaturate and flatten out the three-dimensional effect and colours of the painting. If you’re painting more abstract or impressionistic style works, it can work really well.
www.coldwaxpainting.com is a great resource on Cold Wax Medium techniques.
6. Do you have to Varnish an Oil Painting?
If you’ve followed all the rules of oil painting:
- Fat over lean
- Slow drying over fast
- A well-primed, well made support
You’ll have a stable, durable paint film that doesn’t necessary need a varnish, so no, you don’t have to varnish an Oil painting.
However, varnishes can be used for both their aesthetic and protective properties:
- Change the surface finish to gloss or matte
- Provide a more unified finish to the various areas of a painting
- Increase colour saturation
- Provide protection for the paint surface
- Allow for ease of cleaning
- Provide protection from UV radiation
7. Do you have to dilute the varnish and how many coats do I apply?
It depends on the different brand or type of varnish that you’re using.
For example, MSA varnish needs to be diluted with Turpentine before applying and if using a brush application is best applied with a few thin coats.
Winsor & Newton’s gloss varnish can be applied straight from the jar so read the manufacturers instructions carefully as to understand fully the product you are working with.
When using a spray varnish if you work in several layers, you can judge the sheen and increase the gloss level the more coats you apply. A sprayed coat of varnish will dry within 10 minutes and subsequent coats can then be applied, always allow the previous coat to dry first.
The more coats that are applied the richer and deeper the colours will be.
How to apply a varnish with a brush
Warm the canvas next to the radiator to make sure there is no water in the canvas to prevent blooming.
1. Get a clean, wide brush – I usually use a 2 inch flat nylon brush, you can use a ‘varnish’ brush but it is not essential. I wouldn’t recommend a decorators brush as it will show too many brush marks, you want a brush that is smooth to the touch so you can just glide it over the surface.
2. Pour out some varnish into a shallow dish. It is easier to control the amount of varnish on your brush this way.
3. Lay your work on a board -I use a piece of mdf, or newspaper, you are bound to get some overspray and/or drips.
4. You need to work quick but gently – Apply in long even strokes to cover the surface top to bottom while moving from one side to the other.
5. Work side to side, left to right, slightly overlapping each stroke – you are aiming to have no visible brush-marks
6. Once you leave an area, do not go back over areas that you have done. If you do, you risk dragging partially dry resin into wet, which will dry cloudy over dark colors. If you missed any areas, allow to dry completely and re-varnish. 3 thin coats is better than 1 thick one.
7. After varnishing. I often cover my painting with a board slightly larger than the canvas, resting it on props so it hovers and reduces the amount of dust that could fall on the wet varnish layer. Alternatively with large canvass I will prop them facing a wall when the varnish is semi dry.
How to apply a spray varnish
- Warm the painting so that there is no moisture on the surface – make sure varnishing is never done in a damp or very cold environment.
- Have the spray can at room temperature – not straight out your outhouse or garage.
- Wipe over the surface with a lint free cloth. Make sure it is clean and dry.
- Place your painting vertically in a dust free room. This is very important, it won’t attract as much dust as horizontally and prevents you from being over heavy handed – creating runs.
- Place your painting on top of a board that is larger than the canvas.
- Shake, Shake, Shake… and then shake some more. This is the bit you read on the back of a can and then shake for 10 seconds and eagerly start spraying. Put a timer on your phone, anything to ensure you shake that can for 2 minutes, it’s worth it for an even finish.
- Apply the spray at an even distance away from the canvas. At least 40 cms away, it’s a natural tendency to move your arm closer to the canvas, so just be aware of this.
- Regularly check the nozzle for blockages. It’s the nature of spray varnishes to become blocked really easily but I keep a rag next to me and a practice canvas so I can clean the nozzle, check the spray flow on the practice canvas and go again for real. I find I have to do this several times when I’m spraying a varnish.
- Shake, Shake, Shake… and then shake again.
- Over spray the edge. Start before the canvas and finish after the canvas spraying the board underneath. This ensures an even coverage.
- Work in thin layers. 2-3 layers should be fine, a sprayed coat of varnish will dry within 10 minutes and subsequent coats can then be applied, always allow the previous coat to dry first.
- As many as 20 – 50 coats can be applied for a super glassy effect.
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