SOME CERAMIC MANUFACTURING DEVELOPMENTS 269 



possess these properties and excellent results were obtained from their 

 use.^ These substances were made from kelp. Their most interesting 

 property as a suspending medium was the ability of the alginates when 

 added to water even in small percentages to make solutions of high 

 viscosity. For example, water solutions of ten per cent ammonium 

 alginate would stand stiff. Some of the advantages in our use of 

 alginates for suspending number plate enamel were: (1) uniformity of 

 composition resulting from the alginates being a manufactured product 

 rather than a natural mineral ; (2) the fact that dried sprayed coats of 

 alginate suspended enamel were less subject to damage from handling; 

 (3) a low decomposition temperature which resulted in the material 

 being driven off before fusion of enamel, thus avoiding bubbles in the 

 enamel ; and (4) increased resistance of the finished enamel surfaces to 

 chemical attack and their ability to withstand greater mechanical shock 

 and distortion without damage, since any refractory materials present 

 when the enamel was fired would not be completely fused or incor- 

 porated into the glass, leaving points more readily attacked chemically 

 as well as lines of mechanical weakness. 



Using alginate suspended enamels, suitable manufacturing processes 

 were developed for the application and firing of enamel and the appli- 

 cation of characters to the fired plates. A machine was devised for 

 the application of the sifted coating, and rotary continuous furnaces 

 were installed for the firing operations. 



Originally the decalcomania method was used for character applica- 

 tion. In this process, the enameled parts were first coated with a thin 

 coat of sizing and, after partial drying, they were placed in a locating 

 fixture mounted on a small arbor press and pressure was applied to a 

 properly located transfer by means of a soft rubber pad. The paper 

 backing of the transfer was then removed by soaking in water and, to 

 insure contact, the characters were repressed with a silk covered pad. 

 The sizing was then baked off before firing to remove organic materials 

 and eliminate shadows around the characters. This method was 

 costly and even well trained, careful operators did not produce satis- 

 factory plates. 



To eliminate these defects, an offset printing and dusting method 

 was developed in which an electrotype printing plate was covered with 

 printer's ink and an impression was transferred to the number plate 

 by means of a rubber transfer pad. Powdered vitrifiable colors were 

 then dusted over the entire surface of the plate and the unprinted 

 areas of the part brushed clean with a camel's hair brush. In printing 

 two color plates, the black letters were printed and dusted first, after 



3L. I. Shaw Patent 1,806,183, "Suspension," May 19, 1931. 



