Have you ever noticed how some areas of an oil painting may appear “sunk” or go dull weeks after they are finished? This is a common issue with oil painting yet much neglected technicality in modern painting knowledge. There is a process called “Oiling Out” which rectifies this and is best undertaken before varnishing a fully cured painting,
“Sinking” in colour happens when lower layers of an oil painting or its support are more absorbent than the upper layers. So, this “dullness” is caused by insufficiently prepared supports, or little or no medium mixed in with the oil paint.
As the painting dries, the oil in the upper layers drains out of the top layers to the lower layers or ground. As this occurs, the oil paint closer to the surface becomes “rough”. If you image it in detail cross-section, think of it as pin holes appearing in the paint surface. Vapourisation of the oil mediums also results in an uneven oil paint film which is “rough”, where pin holes are left in the upper layers leading to the lower levels of the painting.
Dullness is caused because light reflectance is lowered on rough surfaces, more so than from smoother ones which produce greater sheen. The aim of “oiling out” is to fill these holes and restore a smooth surface which unifies sheen within the paint colour. In addition “oiling out” provides a thin layer of protection prior to varnishing the fully dried painting. If and when varnish needs to be removed to clean a painting at a later date, it can safely be done without removing any paint.
With traditional techniques linseed oil has been used for “oiling out”, which however tends to yellow. Neither should linseed oil be used with Archival paints as it introduces yet another element which is more brittle than its underlying structure. For traditional oil painting techniques Heat Treated Linseed oil (faster drying) may be used mixed with 50% solvent which will reduce the tendency to yellowing. Alkyd mediums of any type, including Archival Fat, Lean or Classic are not suitable for this process.
Chroma recommends using the Archival Odourless Solvent for oiling out Archival Oil paintings. After the paint surface is dry, moisten a rolled up wad of clean cloth and rub over the surface of the painting. The excess may be gently wiped off. It may also be necessary to repeat this process a few days after or again a third time. A single layer of solvent rub is also a good way to lubricate the top and edges of a painting, bringing back the “wet” colour, to match fresh paint to and continue painting.
Try this process on your work between layers to help match colours or after the final layer is dry and see the difference. It’s a really good way to prepare paintings for exhibition when you don’t have the drying time to varnish them in. Remember to wait between 3-6 months before varnishing a painting.
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Acknowledgment to www.peggyflanders.com/Information/oiling_out.htm, accessed on 11-10-2011 as technical reference.