For some reason oiling out is under emphasized or has been forgotten by many art instructors. Yet it is critical in creating conservation works of art.
Oiling out is the process of applying and rubbing in a thin coat of drying oil (linseed oil) or painting medium to an oil painting. This is done after the surface of the oil painting is sufficiently dry that the oil or medium can be applied without disturbing it. Excess oil can be wiped off afterwards. This saturates the color, restores the sunken areas of the painting and helps isolate the color layer from the final protective varnish.
Oil paintings should always be oiled out when completed and are waiting for sufficient drying before a final protective varnish is applied.
The painting may require more than one oiling out depending on how much the painting has sunk. Oiling out should continue until there are no sunken areas after the painting has dried for several days. Oiling out can also be done between painting sessions to restore sunken areas. However, the painting should always be oiled out when completed and prior to varnishing.
Oil paintings may appear to sink or become dull in areas as they dry because:
- Oil is absorbed out of the upper paint layers into the lower layers or the ground on the painting support. This leaves the upper surface short of oil and microscopic rough. Generally this occurs when the lower layers are more oil absorbent than the upper.
- The oil surface can also become microscopic rough as a result of vaporization of the volatiles in the panting medium leaving pinholes to the deeper layers.
The color appears dull as a result of the difference in light reflection from the rough surface. Oiling out restores the unified reflection surface to the painting. In addition it seals any upper surface pin holes thus when a finial protective varnish is applied it will not contact the color layer allowing it to be removed when necessary for conservation or cleaning.
Even if the painting is not varnished it should be oiled out. This will unify the upper layer and seal the lower color layer from environmental contaminates. The rough surface in the sunken areas will also attract dirt if the painting is not oiled out.
Two quick comments on varnishing:
- Old resin varnishes like Damar should not be used.
- Paintings should never be varnished until the oil is sufficiently dry. Premature varnishing can result with the varnish reacting with the paint film forming a tacky surface that does not dry properly if it ever dries.