JAPANNED AND ENAMELLED LEATHERS 125 



assists the attainment of the desired black colour. The 

 exact details of the boiling, and the manufacture of the 

 varnishes is still largely the trade secret of the master 

 japanners, and differs indeed for the various stages of 

 japanning. The varnish for the earlier coats is boiled 

 longer, and the drying carried further, than in the case of 

 the later coats. This is partly to obtain a product of such 

 stiffness that it will not penetrate the leather. The driers 

 and the pigments should be finely powdered and thoroughly 

 mixed in. The boiling takes several days when at a low 

 temperature, but if done in 24 hours the temperature may 

 be up to 570 F. In the later coats driers are often not 

 used, and the product is often mixed with copal varnish, 

 pyroxylin varnish, etc., which greatly help in obtaining 

 smoothness and gloss. Turpentine, petroleum spirit and 

 other solvents are also used to thin the varnishes. Before 

 boiling, the oil is often purified by a preliminary heating 

 with nitric acid, rose spirit and other oxidizing agents, 

 which precipitate impurities and thereby assist in obtaining 

 a bright gloss. 



Before the application of the varnishes, the leather is 

 first dried thoroughly in a stretched condition. This is 

 accomplished by nailing down on boards which fit like 

 movable shelves into a " stove," a closed chamber heated 

 by steam pipes. The temperature of the stove varies widely 

 in different factories, from I4O-200 F., according to the 

 nature of the varnishes. The first coat of warm and rather 

 stiff japan is laid over the hot leather in a warm room, 

 being spread over first by hand, then by a serrated slicker, 

 and then again smoothed by hand. The goods are then put 

 into the stove for several hours to dry. When dry the 

 surface is pumiced and brushed and a second coat applied 

 in a similar manner, but with increased care. This is 

 repeated with finer japans until the desired result is ob- 

 tained. Brushes are used to apply the later coats. Up to 

 seven coats may be applied for the production of a smooth 

 japan three coats of ground japan, two coats of thinner 

 japan, and two coats of finishing varnish. 



