Page:Popular Science Monthly Volume 90.djvu/609

 How Paints Are Made

The chemist has changed the paint industry. You don't mix your paints nowadays. You buy them ready mixed

By Henry A. Gardner,

Assistant Director, The Institute of Industrial Research, Washington, D. C.

���No, this is not a soup kitchen. It is a room in a varnish factory where the expensive fossil resins are melted in copper kettles of one hiondred-gallons capacity preparatory to mixing and canning

��THE owner of an average house will probably be surprised to learn that every time he paints it about one hundred and fifty pounds of metallic lead and zinc are used. For that reason, the film of paint that series to protect the wood may be thought of as a metal shell.

The average mix- ed paint contains in ^_ ?^*^J'2f**l*2''*^-^^*'*=^«*^

^ . ( 13 an air-ticbt shell protecting the wood

every gallon about ten pounds of lead and zinc that has been transformed into white powders *>y *** = by chemical proc- esses. These white powders, which are called pigments (white lead and white zinc), are ground in linseed oil to produce paints, duced by corroding

��Showing impreg- nation of the wood

��fume which is cooled in long flue pipes. Other forms of white pigments, such as finely ground china clay and talc rock, are used in the paint industry. An almost end- less variety of chemical colors are manu- factured for paint. These colors are made from metals such as lead, zinc, chromium, iron, antimony, cop- per, cobalt and cad- mium, as well as from certain coal tar dyes. Nearly five hundred differ- ent base colors are used by the large paint makers.

���Cross- section of a block of wood showing impregnation of the wood by the paint

��White lead is pro- metallic lead with vinegar and gases or by subliming lead ores in special furnaces. VVhite zinc is produced by heating zinc ores with coal. At a high temperature the zinc forms a white smoky

��Paints are Mixed Like Dough

In making paints, the white pigments are mixed in proper quantities with linseed oil in large mi.xers containing revolving knife blades and stirrers, such as are used in a bakery for mixing bread dough. The paste formed is then run through mills con- taining closely set revolving plates of

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