What is an isolation coat? Traditionally, an isolation coat on a painting is a coat of some kind of gloss medium when you finish a painting. It is transparent and goes between the finished painting and the varnish. It is always a good idea to varnish a finished painting to protect it and add to its longevity.
If being archival is important to you, you can add an isolation coat. If you think that it may not be around for 100 years, you can just varnish it when it has dried completely. This is key because otherwise the varnish will stick to your painting and be a nightmare to try and remove. Varnish is not permanent, it just acts as a dust collector that you can remove and replace, every 10-20 years depending on how dusty the environment your painting is kept in.
Using an Isolation Coat Between Layers
An isolation coat can also be used between layers of paint on a surface. I used several layers of a gloss medium between layers in order to form a barrier so that the next coat of paint can allow you to let whatever you have first put on the canvas remain visible, if that is your plan.
The basic process is do the underpainting. I like to first add color all over my canvas, do some mark making and random colors, let dry, then lay down a thin layer of acrylic gloss medium. That’s the basic process. In that way, if I am basically creating a blue painting, but I want another color showing through, I can paint over it and leave parts of it showing. Perhaps I originally made a very dark mark and I want it to be almost invisible, I can cover it with the second coat of paint.
In this painting I did about three isolation coats somewhere on the canvas and painted over them. I like the process and the effects it gives me. I think that you can see some of the under-details for yourself.
After it dries for about 2 weeks, I will varnish it.