Applying a final varnish to your dry oil painting offers numerous benefits, including protection from scratches, increased color saturation, a uniform surface sheen, and slowed aging. However, it's crucial to wait until the painting is thoroughly dry before varnishing to avoid melding the varnish with still-drying paint, which can result in cracking or wrinkling.
There is often confusion about the appropriate waiting period before applying varnish. While the traditional rule suggests waiting 6-12 months, this timeline doesn't consider the wide range of drying times influenced by factors like paint thickness and the use of fast-drying mediums. Modern synthetic varnishes, such as Gamvar, can be applied when the thickest areas of your painting are dry and firm. Still, it's important not to rush the process and apply varnish too soon.
Artists may be eager to varnish their paintings sooner for exhibition or sale purposes. In such cases, using fast-drying alkyd mediums and painting thinly may allow for varnishing as early as two months. To test dryness, try pressing your thumbnail into the thickest part of the paint, twisting your thumb flat, or wiping with a solvent to check for color removal. Planning a varnishing deadline ahead of an exhibition can help ensure your paintings are finished and adequately dry.
The ideal varnish should not change in appearance, remain flexible, and be removable without affecting the underlying paint. Synthetic resin-based varnishes outperform natural tree sap resins, as they offer better flexibility, removability, and resistance to yellowing or darkening. Some varnishes even provide UV protection.
Before varnishing, store your drying painting in a dust-free environment and clean it with a damp cloth to remove any dust. Avoid the practice of "oiling out" sunken, dull areas, as it can cause yellowing and darkening. Instead, apply a removable final varnish for long-lasting protection and future cleaning.
If you must address sunken patches before varnishing, try applying varnish to those areas first, or oil them out and repaint on top. Retouching varnish can provide temporary protection before applying the final varnish but should not be used to create adhesion between dried layers, as it may make the paint less resistant to solvents over time.