Resin-based thinners that allow the artist to superpose layers of paint more rapidly without the new colours soaking through to the ones underneath. They also ensure that the painting dries better to the core and increase the suppleness of the paint film over time, thus delaying the appearance of cracks. With different combinations, artists can increase or decrease the setting time, change the shading, texture and adjust the brightness and transparency of their work. When using oil paint, be careful never to paint too lean (dilute with solvents instead of mediums): when the varnish is applied, the picture varnish will fusion with the paint layer. The consequences are serious because any future varnish removal and restoration will become impossible.