Investigations have shown that synthetic varnishes studied are remarkably more resistant to cracking and to yellowing than damar and mastic. This is so much so that they may be considered an entirely different class of materials. Experiments have also shown that, during its lifetime, a spirit varnish prepared with damar is expected to be more resistant to cracking than mastic. A scale of hardness has been established for the better known spirit varnishes used in protecting pictures. A fact already known in the field of commercial lacquers has been shown to be equally true in the case of the picture varnishes: the films retain considerable solvent long after they are dry to the touch. The retained solvent definitely affects the properties of the films, usually causing them to be more flexible than they will become in time.