Lacquers as binders

Varnishes are made from resins, drying oils and volatile oils.
Resins can be hard or soft.
The addition of varnish to the binder gives good adhesion of the paint layer to the gesso, increases the internal cohesiveness of the paint layer and facilitates lasering. It also strengthens the structure of the paint layer and reduces the degree of darkening of dyes and makes it resistant to moisture.
In general, resins are more transparent than oils and have a higher gloss than oils, so the oil-resin paint layer has a deeper color saturation than oil alone.
In the process of drying of the paint layer, resins play a major role - they dry quite differently from oil: they slightly reduce their volume only in the stage of volatile oils serving as solvent, later their volume does not change. Therefore, oil particles in the presence of resins are not capable of such volume fluctuations during drying as in pure oil, and the paint layer is not threatened by shrinkage, wrinkling or sharp cracking.
In this case, an important role is played by volatile oils, which, by volatilizing, reduce the volume of the binder in the paints, i.e. they act in the opposite direction of the oil, which in the first phase of drying increases the volume.
The drying process of resins proceeds simultaneously throughout the thickness of the layer starting from the bottom, while oils begin to dry from the surface.
It follows that the addition of resins to oil paints contributes to the even drying of the paint layer and speeds up the process.
The faster drying of oil paints prevents the formation of dull spots. In addition, they have less ability to yellow and darken, as they contain less oil. They improve adhesion to the surface of the canvas and cause the colors to cohere with each other, since the volatile oils contained in them are able to dissolve the resin of the lower layer and thus fuse the individual layers into a single unit.
Resins in solvents including oil should be used for binders, since they do not have elasticity on their own. Hard resins are better suited for these purposes, although, for example, the addition of Venetian turpentine (one of the softest resins) also gives good results.
Composition of the varnish binder:

• turpentine - 1 part,
• mastic varnish - 1 part,
• oil - 1 part.