Making Lacquer Wood Finish
How to make water based lacquer for wood finish.
¶ A brief outline of the manufacture of pyroxylin lacquers is interesting. The word cellulose is the chemist's name for all vegetable fibre. Ordinary cotton and wood are the chief forms of cellulose. Paper is simply a physical combination of cotton and wood vegetable fibres, and waste paper is, therefore, used as well as cotton in the making of lacquers.
¶ The first step in the making of lacquer is the treatment of cotton with a mixture of sulphuric acid and nitric acid. The short-fibre cotton which remains after long-fibre cotton is stripped from the plants is the grade used; it is called linters cotton, and after washing, cleaning and bleaching; it is ready for the acid treatment when it is dry. The cotton takes up the nitric acid and is then called cellulose nitrate, nitrocellulose or nitro-cotton. This nitro-cellulose is washed thoroughly with water and some soda to remove the acid, leaving the nitrogen in the cotton, and then the water is taken out. The water is displaced with alcohol and the nitrocellulose is then called pyroxylin, or soluble cotton. It is shipped in the wet state, containing about 30% of alcohol by weight. The alcohol materially reduces the fire hazard. Pyroxylin is the raw material from which the lacquer manufacturer makes his product. It is also called collodion and is used in surgery for coating wounds.
¶ Nitro-cellulose which contains a great amount of nitrogen, up to 13.5%, is the base of smokeless powder. That which contains more nitrogen is the base for making gun-cotton explosives. The nitro-cellulose used for lacquers, that which makes pyroxylin, is nitrated to an intermediate degree, from 11.8% to 12.5% of nitrogen, and as long as it is kept wet with alcohol there is little or no risk of fire or explosion.
¶ Pyroxylin used as the base for lacquers looks very much like ordinary cotton. It is white, rather solid and the fibres are more brittle. To make lacquer this pyroxylin is dissolved in solvent liquids like ethyl, butyl and amyl acetates, acetone and methyl alcohol. These solvents are, of course, very volatile. Combinations of denatured alcohol and camphor and of alcohol and ether are also used as solvents of pyroxylin. Alone these substances are not solvents, but in the combinations they are.
¶ Then other thinners are added which are volatile but are not solvents of the pyroxylin. They are used simply to make the lacquer more fluid so it can be sprayed on to a surface more easily, or so it will distribute itself better when articles of merchandise are dipped into it. The volatile, non-solvent liquids used in lacquers to make them more fluid, help control the rate of drying and to help decrease the cost are: denatured alcohol, butyl alcohol, fusel oil, benzol, toluol and xylol.
¶ Pyroxylin dissolved in the solvents mentioned and diluted with the non-solvent volatile liquids makes an exceedingly tough and transparent coating, but one which is too brittle and which does not adhere as firmly as is desired to under coats. Therefore to that solution is added what are called plasticisers, or softeners, which remain in the lacquer when dry and increase the elasticity. Castor oil, rape oil, camphor and a group of liquids called esters are used as plasticisers. In order to increase adhesion and the gloss of the lacquer, gum resins, such as are used in making oleo-resinous varnishes of the old type, are added to the solution.
¶ Lacquers made of the materials so far mentioned are very transparent and very light in color, as well as exceedingly tough and resistant to wear of all kinds. In order to make lacquer enamels, color pigments and also opaque pigments are added to the clear lacquer.
¶ The drying of lacquers requires from ten minutes to an hour, depending upon the composition which is within the control of the manufacturers. It dries by the evaporation of the solvent and non-solvent volatile liquids until nothing is left on the surface except the cellulose in the hard, solid form, plus the plasticisers and the gums incorporated.
Next Page: Applying Lacquer.
This is Making Lacquer Wood Finish.
www.craftsman-style.info is Copyright © 2005-12 by International Styles