Artists and art restoration specialists are familiar with both synthetic- and natural varnish in their work.
Natural varnish comes from various ‘natural’ sources as the name suggests. Mastic and dammar resins come from trees. Copal and amber comes from fossilised organic material, and shellac comes directly from insect secretion.
Dammar (also spelt Damar) and Mastic varnishes are soft varnishes and they dissolve in solvents such as Turpentine and Mineral spirits.
Copal and Amber varnishes are hard, and a tad complicated to apply properly because they have to be heated up with hot oil. They are also near impossible to remove from a painting.
The there are pros and cons with using either natural or synthetic varnishes. The old-school natural ones tend to yellow over time, whereas the synthetic types stay clear and flexible over time.