Varnishing is important since it protects the paint from yellowing, dust, and UV radiation. Applying varnish as a final coat will help in the salability of the artwork. Varnishing the painting will increase the vibrance and make it more attractive and alive. There are different varnishes in the market. There are acrylic resin varnishes and acrylic polymer varnishes. Acrylic resin varnishes give high gloss and are clearer.
There are spray/liquid varnishes for acrylic painting and spray/liquid varnishes for oil painting. But make sure that you don’t use acrylic varnishes on oil painting. This will decrease the life of the painting and will cause cracking.
You can apply 2 coats of varnish to paint, but in any case, if it looks uneven you can apply the third coat as well. Brushing the varnish is recommended for a smooth finish, but if the work is textured it is essential to use spray varnish.
[image from milan art institute]