Until recent years, it appears to have been generally supposed that paint used for either the protection or ornamentation of various surfaces must necessarily be applied by means of painters' brushes made of hog's bristles. But it has been clearly demonstrated during the past few years that the application of the paint may be made by means of either total immersion of the article to be painted in a tank or by spraying the paint on to the surface with the aid of compressed air. The rapid increase in the use of both processes is principally due to the immense saving of time which is effected, and this may be approximately estimated at from five to nine-tenths. In other words, one man can do the work of from five to ten men, or even more. To put it another way, if a piece of work costs 20s. for labour in painting by the old process, it may be safely assumed that it can be done by dipping or spraying at a cost of from two to four shillings.
The question will at once suggest itself: "Is paint applied by dipping and spraying as durable as that applied by the brush?" As the paint in the greater part of work of this character is used solely for protective purposes, the question is clearly one of considerable importance. The answer to the question is that when properly prepared paint is used, both methods give an equal, or even better result from the point of view of durability than that which would be obtained if a painter's brush was employed, while, in the case of painting by immersion or by spraying, the paint finds its way into places which a brush could not reach, such as open joints of a waggon, the intricate parts of certain agricultural machinery, the inside of small metal boxes, etc.
Both methods are successfully employed in practically every branch of the engineering, metal and many other trades. Heavy steel sheets may be dipped provided that adequate plant is employed for lowering and raising them into the tank, or they may be sprayed without much difficulty. Children's toys (to take the other extreme), costing less than a penny each, may also be economically painted by dipping. Speaking generally, anything large or small which can be handled or moved by lifting machinery or on a turn table, can be painted by either one process or the other. For example, a hundred or so of very small iron castings, or wrought iron ware, may be placed in a wire basket and dipped together in a few seconds, or the body of a motor car, or parts of a bicycle, can be painted by spraying in a fraction of the time it would take to do the work by means of brushes.