This diversified matter consists of mineral salts and various organic substances, gelatinous in their nature and held in solution by a viscous liquid and containing nitrogenous matter in different combinations, the whole being designated by the general name of albuminous substances. The older the wood the more viscous is the matter; while wood of recent growth (sapwood) contains less viscous matter holding these substances in solution. This albumen in wood acts on substances like filler and varnish in one way or the other, good or bad. The seasoning of wood does not dispose of these substances. The water evaporates, leaving them adhering to the sides of the cells. The drier these substances are the less action they exert on the filler or whatever substance is coated on the surface. If the filler disintegrates, it affects the varnish.

All albuminous substances, be they dry or in liquid form, are subject, more or less, according to the protein they contain—which seems, or rather is, the essential principle of all albuminous matter —to the influence of caustic potash and soda. Thus, the albumen of an egg is exactly like that contained in the composition of wood. As albumen in wood becomes solid by drying, it is easily dissolved again, and will then be acted on chemically by any extraneous substance with which it comes in contact.

Some of the shellacs, substitutes for shellacs, and some of the liquid fillers are manufactured from some of the following substances: Old linseed oil, old varnish, old and hard driers, turpentine, benzine, often gasoline, rosin, whiting, cornstarch flour, hulls, paint skins, silica, and so on. The list is long. To these must be added a large volume of potash, to bring it to and hold it in solution. There must be an excess of potash which is not combined into a chemical compound, which if it did, might mitigate its influence on the albumen of the wood. But as there is potash in its pure state remaining in the solution it necessarily attacks the albumen of the wood, causing disintegration, which releases it from the wood, causing white, grayish flakes, and the formation of a powder. This is not a conclusion drawn from an inference but an established scientific fact resulting from experiments with fillers the various compositions of which were known. All alkalies act on albumen. No one would knowingly varnish over a surface such as it would be were the white of an egg applied to it and then washed with an alkali solution; but that is just what is done when varnish is put over a wood surface filled with a filler which contains an alkali.

Most of the combinations of material used in the painting trade are mixtures; that is, each part remains the same— exerting the same chemical action on another substance, or any other substance coming in contact with a paint mixture will exert the same chemical action on any part, or on any ingredient it contains, the same as if that part was by itself.

We can now account for some of the numerous peculiarities of varnish. We know that any alkali when coming in contact with albumen forms a compound, which on drying is a white, brittle substance easily disintegrated. This is why potash, sal soda, and kindred substances will remove paint. The alkali attacks the albumen in the oil, softening it, causing easy removal, whereas if it were allowed to dry, the albumen in the oil would take on a grayish color quite brittle. Potash or other alkalies in filler not only attack the albumen in the wood, but also attack the albumen in the oil by forming a compound with it. Probably this compound is very slight, only forming a compound in part, enough, nevertheless, to start a destroying influence, which is demonstrated by the following results of experiments. The reader has, perhaps, some time in his career applied a rosin varnish over a potash filler and has been surprised by the good results, a more permanent effect being obtained than in other instances where the best of varnish was used. This is accounted for by the rosin of the potash. Again, the reader may have had occasion to remove varnish with potash and found that potash would not touch it. This is because of its being a rosin varnish. Potash in filler may be rendered somewhat inert, by reason of its compounding with other parts of the filler, but owing to the quantity used in some of the commercial fillers it is not possible that all the alkali is rendered inert. Hence it will attack the albumen wherever found, as all albumen is identical in its chemical composition.

Alkalies have but little effect on the higher classes of gums, because of their effect on the albumen in the wood and oil. All alcohol varnishes or varnishes made by the aid of heat stand well over an alkali filler. Varnishes which contain little oil seem to stand well. This is accounted for by the fact that alcohol renders albumen insoluble. Alkalies of all kinds readily attack shellac and several other of the cheap gums, forming unstable compounds on which oil has but little effect.