Acrylic paints and varnish
Does a coat of varnish help to bind acrylic paint to the surface?
Ask Jacksons: I have read that acrylic paint should not be diluted too much with water as it reduces the binding properties. Does a coat of varnish help to bind the paint to the surface or would there be long-term problems?
We recommend only using an acrylic medium, as you’re right that the film of acrylic paint becomes very weak if it’s diluted too much. This is because the pigment is held to the surface with very little binder and will be prone to abrasion or even could be brushed off. Generally, you need to keep your water to acrylic paint mix ratio to at least 50% paint to 50% water. It’s fine if you want a watercolour effect, or if you have no intention of selling it, but if you do intend to, you should really only use a medium.
While a varnish would bind even a weak layer of paint, or rather pigment, to the surface without trouble, using a brush-on varnish will disturb the earlier dried acrylic layer. So, if it’s a very diluted wash, consider using a spray acrylic varnish, as it won’t brush the pigment, but be aware that spray varnishes can be very difficult to apply evenly. Browse acrylic varnishes on Jackson's website.
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