If a painting has lost its vitality and become dull, all may not be lost. This usually occurs due to what is known as “sinking”, when the top layer of oil has been lost to the layer underneath. There are three common causes: an over-absorbent surface, using too much solvent, or not using enough medium. Using the “oiling out” technique can give the painting a new lease of life.
As ever, prevention is better than cure, and the best way to avoid sinking on oil paintings is to apply artists’ primer such as Oil Painting Primer to the surface before you start.
But as you build up oil colour in layers, the different drying rates can result in a paint film with varying degrees of absorbency, which show up as dull spots rather than a complete dull area. The trick is to treat these dull areas as soon as they are dry. Apply Artists’ Painting Medium sparingly to a clean cloth and rub gently into any sunken areas. Wipe off any residue and leave to dry for a day or two.
If you can still see smaller dull areas then repeat the process until the painting has regained an even sheen. Avoid using varnishes to refresh a dead painting. For a faster-drying oiling out medium, use Thickened Linseed Oil diluted with 50% white spirit (mineral spirits).