What is an isolation coat?
An isolation coat is a coat between your finished painting and the varnish.
It is transparent and creates a physical separation between the varnish and your painting.
This is key because otherwise the varnish will stick to your painting and be a nightmare to try and remove. The varnish is not permanent, it just acts as a dust collector that you can remove and replace, every 5 to 10 years depending on how dusty the environment your painting is kept in.
To make an isolation coat I use GOLDEN Soft gel gloss. This medium is off the hook, and I highly recommend you buy it along with an Acrylic Glazing Liquid Gloss if you are starting acrylic painting. These bad boys are all you need.
Alternatively, Golden has recently released a pre-mixed isolation coat you can use.
A full-gloss finish can do amazing things to your paintings…
Step 1: How to apply an isolation coat to an Acrylic painting
Checklist before applying an isolation coat:
- Make sure the painting is 100% dry, ideally leave at least 24hrs before applying an isolation coat.
- Look over the surface of the painting up close to see you don’t have any rogue brush hairs on the surface.
- Photograph your painting. It is soooooo much easier to photograph a surface with a matte finish. The gloss of the isolation coat will reflect everything and if you can’t turn off the flash on your camera, the light from the flash will bounce off the reflective surface.
- Sign your work, a signature under gloss just looks lovely.
- Use a clean brush and then only use this brush for varnish, 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, clean is good for isolation coat or varnish.
- A flat, dust-free area. You need to be able to leave the painting in this position for an hour or two
Pro tip: If you are coating the sides of canvas you can slightly raise each corner with a small piece of wood so the painting doesn’t stick to the surface below.
Pro tip: If you want a matte finish and have used an absorbent ground (such as ground for pastels) it is important to add an isolation coat. Even though it seems counter-intuitive to put a gloss isolation coat down first then put another matte varnish coat on top. If you left it without the isolation coat the matting agent in the varnish would remain on the surface, the solvent would be absorbed into the ground resulting in a white residue.
Step 2: How to mix your isolation coat
You’ll only have to mix an isolation coat if you’re using soft gel gloss, the pre-mixed isolation coat is ready to go straight from the pot.
1. Mix two parts soft gel gloss to one part water – Mix more than you think you will need, trying to match the exact consistency if you run out is not fun!
2. Add the water – little by little as it will mix in better.
3. Do not be tempted to add more water
4. Re-read point 3 – the mixture will appear too thick, too white, and just a little scary, it isn’t.
5. 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.
6. Lay your work on a board -I use a piece of MDF, or newspaper, you are bound to get some overspray and/or drips.
7. You need to work quick – paint the soft gel gloss over your painting in all directions to make sure you don’t miss a bit. (Don’t be tempted to go over semi-dry areas as it can easily pull up the isolation coat.)
8. Work side to side, left to right, slightly overlapping each stroke – you are aiming to have no visible brush-marks
9. Squeeze out excess soft gel gloss from your brush so it is practically dry, smoothing out any raised areas of soft gel gloss.
10. Gently brush over the surface – check the sides for any overruns, get down to eye level with the painting and look at the reflection at an angle, this helps you to see if you have missed any bits.
11. Leave to dry
An uneven finish to a painting, some parts matte, others gloss can be very off-putting to the viewer.
A unified finish both enhances the colours and it can be a great way to add a professional finish to your paintings to add dollars to the sale price.
One final thought if you’ve never applied an isolation coat before.
Making a Test Varnish
If you’ve never used an isolation coat (or applied a varnish) your best investment to achieve a good result is to practice.
Just don’t practice on a painting you’ve been working on for weeks.
Make a few small test pieces (6 x 4 inch) and paint them with a range of solid colours.
The test pieces can be made on thick card or scrap canvas, make sure you have one that is dark, preferably black so you can see how a matte or glossy finish alters the final finish.
Then you can try a variety of brush applications and different finishes of varnish until you find the perfect combination for the aesthetic you’re after.
Pro tip: If you’re not sure if your painting is finished, or you are nervous about varnishing it, you can leave an isolation coat on for ages, and then repaint on top in the future. Just bear in mind the surface will be super slippy and won’t soak up moisture (see: How to paint over an acrylic painting) so paint thick!
You might also like:
Golden 236ml Soft Gel Gloss