Varnishes and resins

Varnishes (varnishes) are of great importance in painting as an additive to binders and as a coating (final) varnish.
Varnishes are solutions of resins in various solvents.
Types of varnishes:

• oil-based,
• turpentine,
• spirit-based.

Uses:

• as additives to paint binders, especially laser binders;
• as an additive to emulsions (in tempera binders);
• as a thin film insulating the painting layers (in Dutch tempera;
• as a final varnish.

The coating varnish should meet the following conditions:

1. It should protect the painting from destructive atmospheric influences (pollution, temperature, moisture, gases).
2. It should be compact and flexible, so that the paint layer can normally "work" under conditions of varying temperature and humidity.
3. It must not reduce the flexibility of the paint layer and canvas.
4. It must be colorless and transparent.
5. It should spread easily in a thin layer.
6. It must not form bubbles.
7. It must be easily removable.
8. Must not have too much gloss.
9. It should protect the painting from external injury and contamination.

Sometimes the coating varnish is deliberately colored.
Most old paintings have a layer of yellowed varnish.
Oil paintings require varnish due to the decomposition and blackening of some hydrogen sulfide-sensitive pigments (lead, copper). A coat of varnish insulates the painting from these influences.
Since varnishes yellow over time, they must be removed from time to time.
In order to remove the varnish without damaging the surface of the painting, soft resins, such as homemade or mastic, dissolved in aqueous oils should be used.