Seal the deal – 12 Tips To Seal Your Finished Acrylic Canvas.

You’ve finished your next masterpiece – well done! Enjoy that sense of satisfaction, but don’t hang it on the wall just yet!

In this article we’re going to discuss 12 methods to seal the painting, stopping the colours from fading, and protecting your canvas for years to come.

Why do I need to seal my artwork?

As you are aware, your acrylic paint is water-based. Acrylic is easy to use, and it dries much more rapidly than oils, but the downside of this is, as the paint dries, so the colours become less vivid.

Dry acrylic paint is also relatively soft so that it can be quite easily damaged. Also, fine micro-holes are left naturally in the surface of the material, and these can collect dust. Acrylic paint anyway attracts dust.

So, how do I protect it?

You can put it under glass, to protect it and keep it dust-and-damage free, but this is not a preferred route for many. You are likely to add glare on the surface and lose some of the vibrancy. Glass might make the colours even more muted.

The alternative (and our recommendation) is to apply a protective coat to the paint surface, which can enhance the colours (restoring the vivacity lost when the colours were dulled by the paint drying out), but which will also make the surface more protective and dust proofed. This outer layer will help mitigate against extremes of temperature and humidity. Also, it is easier to clean: Trying to take the dust off an untreated acrylic surface is fraught with difficulty and endangers your artwork.

You know how a pebble on the beach can be so many beautiful colours when wet, but just dull and monochrome when dry? Using a protective coat can restore and protect those ‘wet-look’ colours.

What about varnish?

The generic term used for what you are doing is ‘varnish’ but that is a little deceptive. Traditional varnish is quite old fashioned, and there are problems with it, the main one being that it tends to turn yellow with age, known in the industry as ‘ambering’. Natural varnish usually contains resin, oil and other products, diluted. I don’t recommend it.

If we want to apply a protective, clear coat which is not a varnish but does the same job, what are our other alternatives? There are products called variously, urethane or polyurethane and also polycyclic. Polyurethanes are made from oil and water; polycyclic are water-based.

Either of these types of product will do the job, but they have advantages and disadvantages of their own. Polyurethanes are an oil/water mixture and are still prone to ‘ambering’ over time (though less badly than varnishes). It may be necessary to remove and reapply the coating at intervals, to keep the colours bright. Because of this, you will need a layer between the surface of the paint and the protective coat. This intermediate layer is usually called an isolation coat. The purpose of this is to create a barrier between the acrylic and the protective layer, so if you have to strip back the protective coating to reapply it, the thinner used will not impact on the paint.

Polycyclics, on the other hand, do not amber but to tend to be somewhat thicker when applied. This thickness can be a problem when you are applying polycyclics with a brush, and there is a risk of leaving brush strokes.

The surface of the paint will influence the decision. Is it raised/layered? If your canvas is too impasto then a protective coat, if brushed on, may form pools and this will spoil the effect. Where this is true, a spray might be a better choice.

It is also possible to apply these products using a foam brush, which will mitigate against brush strokes.

My recommendations are as follows:

1.   Protective glass will not give the best result and is not recommended

2.   Using some protection is recommended and will enhance and emphasise the colours

3.   If you want to photograph or scan your painting, consider doing this before you apply any protective layer. You will expect some reflection from the top layer which will make imaging your artwork less successful afterwards

4.   Choose gloss or matte, but not a mix, of course

5.   If your paint is thick and layered, polyurethane may be the better solution. It applies in a thinner layer and is self-levelling. For a very built-up surface, use spray rather than brush application (you can always choose to use spray anyway if you wish)

6.   If your painted surface is very flat, look at polycyclic which is water-based and will be faster drying

7.   It is essential before you start that you ensure the surface is free of dust and lint-free.

8.   You will need several coats of the protective layer, whichever solution you choose. The acrylic paint needs to be completely dry before you start, and each layer needs to be dry before you apply the next one. Ideally, you need to leave the painting in one place whilst each coat dries, and this needs to be a dust-free environment

9.   Each coat needs to be as thin as you can manage and at a uniform covering over the whole surface of the canvas

10. How many coats? Up to you. Probably a minimum of three, but you might want to add more to create a gleaming surface. It depends on the subject, colours and your personal preference.

11. If using a brush, work in long, even strokes, each one slightly overlapping the previous one and work from one side of the painting to the other. Try not to leave gaps but if you realise you have, carry on – do not attempt ‘patch’ them – better to finish, let the coat dry, then go back and treat the area which you missed.

12. If a spray is your chosen solution, you have a couple of other things to consider. Arrange your working space so that you can reach the whole surface of the picture with the nozzle at a constant distance. Also, shake the can, then shake it some more – more really is better, here. Keep an eye on the spray nozzle, which can become blocked, and clean it anyway between coats: Start each coat cleanly

And there you have it! A beautiful, protective covering, tougher by far than the acrylic paint itself and enhancing the lovely colours, letting them shine through