How To Varnish An Acrylic Painting: Everything You Need To Know

Varnishing an Acrylic Painting

When you're ready to varnish, make sure that the painting is completely dry first. If it's the slightest bit wet, the varnish will mix with the wet paint and streak across the canvas. Unless that is your desired effect (hey, why not?), you will want to avoid this. Also make sure that the surface is free from dust, dirt, and any other undesirable things like lint.

To varnish, always keep a separate glass jar or plastic cup aside exclusively for varnishing. Don't use the same jar you use to dip your paintbrush in as you are painting! The reason is that there will inevitably be little bits of paint stuck and dried to the inside, outside, or lip of the jar. If these get into your varnish or onto your varnishing brush, they will then stick to your painting. Not cool! Likewise, I keep a separate brush just for varnishing, for the same reason. You can see and read about the brush I use for varnishing (Amazon affiliate link). It's definitely worthwhile to keep a special brush aside just for varnishing. Because it won't be used frequently (unless you create a lot of paintings at a phenomenal pace), it will last a long time. Therefore, it's well-worth the small investment!

Rinse the jar in water before putting in varnish, because rinsing will wash out major dust particles. Likewise, give your varnishing brush a quick rinse as well.

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If you're using a water-based varnish like I am, then in the jar, mix the correct ratio of varnish and water as instructed on the bottle of varnish. (If you're using a Mineral Spirit Acrylic Varnish (MSA Varnish), do not mix the varnish with water, and instead follow the instructions on the bottle.) Try to mix out more than you think you'll need, to ensure that you'll have enough to varnish the painting in one go. It may take some practice to get this amount just right, but you'll soon get it as you learn how to varnish an acrylic painting. You can even save any unused varnish. I would just put a solid covering (like a lid, or something heavy like a book, or plastic wrap held in place with a rubber band) over the top of the jar, and then use it again in a couple days when I had finished another painting. I would recommend not keeping the varnish mixture for more than a few days though, because it does get cloudy. It's probably fine, but as a perfectionist I'd rather mix a whole new varnish concoction.

I use Golden Waterborne Varnish, which I also discuss here. This varnish is removable, so if for any reason it needed to be removed, it can be removed with an ammonia solution. For my own art, I've never had the need to remove the varnish, but it still seems comforting to have that option. Art conservationists say that it's preferable to have the removability option, in case the varnish somehow yellows or something needs to be cleaned. It's important to keep the longevity of the artwork in mind... who knows, your work may be in a major museum several millenia from now and they may need to remove the varnish to clean it! Why not make their job easier? ;)

If you use a removable varnish and you think that someday the varnish might need to be removed for any reason, you'll need to apply an isolation coat before you varnish the painting. The isolation coat acts as a barrier between your painting and the varnish, protecting your painting from the chemicals that remove the varnish.

To apply an isolation coat, use an acrylic gel medium or gel gloss such as Golden Soft Gel Gloss, diluted with water. For example, the packaging for Golden Soft Gel Gloss recommends mixing 2 parts Soft Gel Gloss to 1 part water, but follow whatever instructions are on the gloss medium or gel gloss that you choose. To apply the isolation coat, follow the basic steps outlined here for varnishing, because the process is similar, and allow at least 24 hours or more for the isolation coat to completely dry before applying your varnish.

If you want to know more about applying an isolation coat, check out this handy page on the Golden website, which also includes a note of caution because "isolation coats are also significant and permanent additions to a painting and inevitably will cause changes in the painting's surface qualities." Read more at the aforementioned link! (Also, note that you can still use a removable varnish on your painting, even if you don't apply an isolation coat - the varnish will still protect the painting, but it's best to never remove the varnish or you'll risk damaging the painting.)