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Coloring Finishing And Painting Wood
Polymerization is a very technical term that is hard to understand by anyone who is not a trained chemist. In brief, polymerization is a change in the molecules of a substance into new molecules which have the same percentage of each component but which possess a higher molecular weight that is always a simple multiple of the original atomic weight. The physical change as a result of polymerization is very marked and striking, and the drying reactions also differ to some extent from those of the linseed-oil type of varnishes. Films that dry largely by polymerization seem to dry at a rather uniform rate from top to bottom instead of skin ning over on top as is common with the linseed-oil-fossilresin type of varnishes.
Drying-oils are placed in varnishes in order to produce more elasticity, furnish greater toughness, and to add waterproofness to coatings made from them. Spirit-varnishes, such as shellac or dammar-varnish, contain no drying-oil and lack elasticity, toughness, and waterproofness which are essential characteristics for floor varnishes and for all finishes for outdoor exposure.
China-wood oil is reported by some varnish authorities to be used almost exclusively in the manufacture of modern architectural varnishes. Small amounts of linseed-oil are, however, necessary in the preparatory heat treatment of the China-wood oil.
The fatty acids found in linseed-oil and China-wood oil are quite different. In linseed-oil the acids are: palmitic 9%, oleic 15%, linoleic 41%, and linolenic 35%. China-wood oil is said to contain palmitic acid 5%, oleic 15%, and eleostearic acid 80%. The fatty acids are quite different and their drying characteristics also differ widely. The very valuable properties of China-wood oil are said to come from its exceptionally high content of eleostearic acid, which is not a component part of linseed-oil. The two oils both contain palmitic acid, and many of their properties are quite similar.
