How Long To Let Acrylic Paint Dry Before Clear Coat

varnishing_an acrylic painting An uneven finish in your painting, some parts matte, other parts glossy can be very off-putting to the viewer.

A unified finish enhances the colours and is a great way to add both a professional finish to your paintings and add dollars to the sale price.

No one technique for varnishing suits every situation. The texture of the paint surface, the desired finish, speed of completion, etc all affect which technique is best to use.

On a side note, it's also the number 1 trick to making your acrylic paintings look like oils…

Varnishing Acrylic Paintings

What exactly is a Varnish?
A thin protective layer between the finished painting and the atmosphere. It should be transparent, colourless and form a good bond with the paint surface yet still be removable without affecting the painting. It is usually a combination of a resin and a solvent and applied to the painting when it thoroughly dry – with acrylics this can be within 24 hrs.

Acrylics attract dirt
Acrylics are different than oils because they are more flexible when they dry leaving a softer exterior than oils.

This makes it easier for dirt and dust to adhere to, this soft skin can make removal of varnish tricky so some tutors advise placing your acrylics behind glass and not varnishing.

However, I have always varnished my paintings following a proper procedure as I prefer the aesthetic without glass.

With the right varnish and technique, it can not only benefit the longevity of the painting but enhance the finish – turning matte to gloss and bringing the colours to a new vibrancy.

Why?

When acrylic paint dries and the water evaporates off, small droplets of the polymer (the binder of acrylic paints is an acrylic polymer) join together to form one mass – this holds the key to the softness.

They also leave very tiny micropores that are left open to the elements and these again collect dust.

If you cover the paint with a harder surface it will help to protect it from extremes of temperature or humidity, it also provides a layer that can be cleaned, rather than trying to remove dust particles ingrained in the paint layer.

If in future the varnish will need to be removed, taking away all the dust and dirt with it, and replaced with a fresh coat you need to be able to wipe the varnish back without disturbing the paint. For this, you need an isolation coat.

What is an isolation coat?

An isolation coat is a transparent layer of a medium that physically separates the underlying layer of paint from the varnish to be applied.

When a solvent is used to dissolve the varnish, the isolating layer will prevent it from reaching the paint layers, where damage could occur.

Golden Soft Gel (Gloss) thinned with water is a suitable isolation coat. It provides adequate levelling and foam release. See (How to apply an isolation coat to acrylics)

Pro tip: The isolating layer is also of critical importance when applying a matte varnish over an absorbent surface to prevent a cloudy or "frosted" appearance from occurring. This frosted appearance results from the varnish and solvent being absorbed into the support while the matting agent remains exposed on the surface, where it appears as a white solid.

Think of it like a wedding cake.

The cake mix is the paint, soft and moveable. The next marzipan layer is the isolation coat, slightly thicker but still flexible, the final icing layer is the varnish – harder, slightly more brittle but protects the cake inside.

Step 1: Should I choose spray or brush?

I recommend brushing varnish for works that are quite smooth in finish and are non-moveable. i.e acrylics, oils. However, if the surface is too impasto pools of varnish will settle in the nooks.

I'll always assess the surface and texture to see what is more applicable, brush or spray. If you have delicate multimedia pieces or highly textural works spray varnish will be the way to go.

Pro tip: If you are using pastels or chalk it is advisable to fix them first with a pastel fixative.

How to prepare for varnishing with a brush

Make sure you have applied an isolation coat.
Wipe over the surface with a lint-free cloth. Make sure it is clean and dry.
Place your painting on the horizontal in a dust free room. If you are varnishing the sides of a canvas you can slightly raise each corner with a small piece of wood so the painting doesn't stick to the surface below.
Use a clean brush and then only use this brush for varnishing, it will be tempting if you are in a rush to use another brush that you 'think' is completely clean. I've done it before and the polyurethane loosened off dried on acrylic paint and went over the painting, not a good idea.
Find a clean jar, same reason as the brush, varnish loves clean!
A flat, dust-free area. You need to be able to leave the painting in this position for an hour or two

Step 2: How to apply a varnish with a brush

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 quickly 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 by 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 colours. If you missed any areas, allow drying completely and re-varnish. 3 thin coats are 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 a large canvas, I will prop them facing a wall when the varnish is semi-dry.

How to apply a spray varnish

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 30 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.
Overspray the edge. Start with 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 but can be as many as 20 – 50 for a super glassy effect. This is personal preference, so experiment.

Understanding the 7 key functions of a Varnish

1. Change the surface finish to gloss
2. Making the surface more matte
3. Provide a more unified finish to the various areas of a painting
4. Increase colour saturation
5. Protection for the paint surface
6. Allow for ease of cleaning
7. Protection from UV radiation

Increase colour saturation & sheen

Have you ever noticed how much better paving look when it's raining? The reflection of the water on the paving slabs makes them look fantastic, the same is true of colours in paintings.

When a permanent gloss sheen is on a pigment it looks richer and more saturated.

In an Oil painting initially, it is the oil that gives the glossy effect, however, over time as the oil dries out it is actually the varnish that gives the sheen.

Different finishes of the same brand can usually be intermixed within each product type or used sequentially, to achieve any desired level of gloss.

Pro Tip: A word of warning when using a matte varnish, if not correctly mixed the matting agent (which is white) can sometimes leave a milky finish to your paintings. This is particularly noticeable on blacks.

Protection & ease of cleaning the paint surface

As varnish has a harder surface than the dried Acrylic paint it helps protect it.

When an isolation coat and varnish are applied correctly, the painting will be able to be cleaned easily. Used correctly the thinners used to remove the varnish will not penetrate the isolation coat and damage the paint film.

Protection from UV radiation

Ultra Violet Light Stabilizers, which can be found in some modern varnishes disperse UV radiation before they hit the surface of a painting. These varnishes are especially useful if you're using materials that haven't got a great lightfastness. It won't render the surface completely lightfast but will considerably lessen the effects.

If you have any other questions about varnishing leave a comment in the box below.

You might also like:

1. James Bernstein, Conservator of Fine Paintings offers a more technical description of varnishing acrylic paintings on the Golden Acrylic website.
2.How to apply an Isolation Coat to an acrylic painting
3. The 3 reasons why artists varnish their paintings, and why some artists don't
4. 7 Questions to ask yourself before varnishing an oil painting