The Golden State: Where & How to Live, Secure, Visit, Enjoy and Thrive in California
Coloring Finishing And Painting Wood
The user of shellac 40 or 50 years ago bought orange flake shellac in the form of thin scales varying in size up to about three-quarters of an inch in diameter. Wood alcohol was the solvent which the shop finisher used in preparing his orange shellac. "White shellac was made from chunks of bleached shellac which dissolved with difficulty in wood alcohol, especially if the shellac was old and had been exposed to the air for some time. Today, either orange or white shellac in liquid form of various strengths dissolved in denatured grain alcohol can be obtained from almost any dealer in finishing supplies. Some of the cheaper liquid shellacs of today are made with a solvent which is a mixture of grain and wood alcohol. Such a shellac produces a disagreeable odor when it is being applied.
Shellac-varnishes may be thinned with cold denatured alcohol and can then be used in a very short time. Coatings of shellac-varnish dry very quickly and produce a low gloss or semilustrous finish. Shellac-varnish is often used on floors and for some other finishes. Shellac coatings will turn white if exposed to the weather or spotted with water. Contractors often prefer shellac as a floor finish because it is easy to apply, dries quickly, and produces a good effect. Shellac is generally unsatisfactory for floors because it does not wear long or well, and turns white if water comes in contact with it. Shellac somewhat diluted is often used for an undercoat or as a sealer. It should be sanded well before another finish is applied over it in order to secure smoothness and aid in the adhesion of the next coating.
321. Oil-Varnishes with Linseed-Oil.—Varnishes made from fossil resins, ester-gum, or treated rosin, which can be melted to liquid form at great heat and then combined with linseed-oil in large part, have been the standard slow-drying varnishes that have been in use in some of their forms for centuries. Metallic driers of several types have usually been added in small amounts to speed-up drying or oxidation. An excess of drier cannot be added to increase the drying speed because of various difficulties that are impossible to overcome. In the old oil or oleoresinous varnishes, turpentine was placed in the mixture as a thinner or volatile solvent; but, for some years, this excellent solvent has been replaced very largely by some mineral spirit or a cheap petroleum volatile oil.
It is thru the evaporation of the thinner or solvent, and the slower changes in the drying-oil, which the chemists say is largely oxidation, that a linseed-oil varnish including fossil resins dries out and changes from a liquid to a solid film. There is a rather marked chemical change during the oxidation of drying-oils, such as linseed-oil, and the new substance formed has molecules which contain additional atoms of oxygen.
