Iron fillers for surfacing castings and hiding the imperfections thereof are usually sold in paste form, so that they may be used as a plaster or putty, applying same with a wide spatula or broad knife, a sort of knifing-in operation and also as a brush coat when thinned with benzine or turpentine substitute. The color is usually a nearly jet black, but steel color is also used to some extent. While white lead was at one time the most costly ingredient in the steel colored fillers, it has given way to zinc oxide or lithopone, and very little of these enters into these paste paints. Black filler is the chief ingredient in most iron fillers, but some are based on barytes and whiting, with lampblack as the coloring principle. The vehicle is composed of raw linseed oil and strong liquid driers, with the latter predominating.
The very low price at which these goods are sold nowadays precludes the use of high grade japan driers.
A fairly good iron filler for use as a plaster putty in its paste form or as a brush coat when thinned with substitute turps or benzine can be produced on this plan, but is best made in a putty chaser: - Sixty-five pounds mineral black filler, 17 pounds common whiting, 8 pounds raw linseed oil, 12 pounds liquid drier (containing gum binder and benzine thinner), total 102 pounds, resulting in 100 pounds product. When this is to be applied to castings a portion of the paste should be thinned with benzine and a coat applied over all of the casting, otherwise the filler will not hold, and when the filler is applied with the spatula as a surfacer, it must be wet up some with benzine or turpentine, so as to level down smoothly.
Steel Color Machinery Paste Paints are thinned by the consumer with substitute turpentine or benzine, as the case may be, and applied with the brush, drying flat, thus hiding any imperfections that may be in the metal. They are as a rule furnished in several shades, light, medium and dark. The pigment usually consists of lampblack, barytes and whiting, or lampblack and whiting alone, with enough zinc oxide or lithopone to produce the desired shade. When the thinned paint is used for dipping, the best policy is to omit barytes entirely, thus avoiding precipitation of sediment. A medium shade of this form of steel color paste can be produced on the following plan: - Three pounds dry grinders' lampblack, 8 pounds lithopone white, 65 pounds Paris white, 10 pounds raw linseed oil, 16 pounds strong liquid driers, ground in one run through a 30-inch mill; net result, 100 pounds.
Machinery Gloss Paints or Enamels are bought mostly in the ready for use form, and when intended for decorative purposes on machine tools, looms, etc., they are simply colors ground in oil or varnish, reduced to liquid consistency with moderate priced mixing varnishes. When desired, however, for engine work in power houses and engine rooms, where a decorative effect is desired, higher grade goods are in demand. While in many places the work is done by the application of colors ground in japan, especially where the work is to be striped and finally finished in clear varnish, there is still a demand for engine enamels, and here the color must be ground in a suitable varnish and thinned with a varnish that is to hold its gloss under the effects of steam vapors and heat. It is essential to ascertain by tests what varnish will stand such conditions.