In my opinion, every painting needs a good coat of varnish. Varnish brings out the best in the colours of a painting and especially the dark hues get a deeper and richer look. Varnish protects the painting and makes it easier to dust and wipe clean, yet many artists fail to varnish their oil and acrylic paintings. I see this frequently at markets and it is a pity. It is also unprofessional if you are selling your paintings.