What is a Varnish Dryer?
The term varnish is used to designate any solution, which, when spread with a brush in a thin layer on the surface of an object, dries with a smooth, lustrous, transparent film. Varnish has very good resistance against abrasion, wear, heat, solvents and water vapour. Varnish should be dried as quicker as possible after its application as there are chances for more dust to settle in the finish if it has a longer drying time. Varnish dryers are solutions of the metal salts of organic acids dissolved in mineral spirits. They are used in paints and varnishes to help the oils dry. They are sold based on the metal content of the solution, i.e. the cobalt dryer contains 6% cobalt metal. The varnish dryers are cobalt, calcium, manganese, zirconium, etc. Varnish dryer is an additive used to improve drying times. It is ideally used for cool or humid areas, for external projects when rain is expected or for reducing the time of projects which require multiple coats. The linseed oil used in oil varnishes is boiled with the addition of certain so-called dryers, of which red lead and certain compounds of manganese treated in various ways are the most important. The dryer is introduced into the oil, either directly or through the medium of the resins of lead and manganese. Linseed oil gains from 14 to 16% in weight in drying, due to the oxygen it absorbs.
Characteristics of a Good Varnish Dryer
A good dryer should dry twenty parts of oil in 12 to 24 hours at the longest. The dryer should mix readily with the oil, otherwise if it separates and is insoluble, it can be put aside as of little value. The behaviour in drying should also be noted. The film of oil should dry smooth and free from crinkles and or other imperfections. Comparisons between different dryers can be made easily by this method of adding fixed, accurately measured proportions of dryer to raw oil and observing the action of the mixtures side by side. A fluid ounce of liquid contains 480 drops. 24 drops of dryer to the ounce of raw linseed oil would be about 1 part to 20. Varnishes can be tested by spreading them on glass and observing their action in drying and the nature of the surfaces they produce. Exposure to steam and the weather will develop their wearing qualities or lack of them.