SOME CERAMIC MANUFACTURING DEVELOPMENTS 271 



ink varnishes.* Motor driven presses using this ink were also devel- 

 oped to faciHtate the printing operations.^ 



The manufacture of these parts was undertaken primarily to 

 ehminate an undesirable supply situation but Western Electric manu- 

 facture resulted in improvements in quality of enameling, quality of 

 printing, and in mechanical strength. This latter characteristic was 

 important since it reduced assembly losses from cracked plates. 



While vitreous enameled copper base number plates have been 

 replaced by other types, the developments outlined were the basis of 

 subsequent enameling developments. 



Vitreous Enameled Iron Base Number Plates 

 The low level of illumination at some pay stations led to the design 

 by the Bell Telephone Laboratories of a large iron base number plate, 

 shown in Fig. 6, to be mounted flush with the finger wheel of the dial. 

 Since the demand for these plates was relatively small, they were 

 originally made by the usual process followed in the industry in enamel- 

 ing similar articles. This process consisted of applying and firing one 

 ground coat for adherence and then applying and firing two sprayed 

 cover coats to obtain the whiteness and opacity desired; all being 

 felspar enamels. The whiteness was not as good as that obtained on 

 the copper base plates with lead enamels and in addition considerable 

 difficulty was experienced in the field due to the fading of the characters 

 as a result of chemical action on plates exposed to corrosive gases such 

 as sulphurous fumes in certain locations. The process was also costly. 

 Since maximum whiteness and opacity was obtainable in the lead- 

 arsenic type of enamels previously described when applied by dusting 

 on dry, it was desirable that the coating be applied in this manner. 

 In order to avoid several enamel applications and firings, it was also 

 desirable that other portions of the plate be protected by some corrosion 

 resistant coating other than vitreous enamel which would necessarily 

 have to retain such corrosion resisting properties after exposure to a 

 temperature of 1500° F. for six minutes and also be capable of being 

 enameled with satisfactory results. Numerous coatings were tried and 

 it was found that a Western Electric black oxide finish on iron would 

 satisfactorily meet all requirements.^ Using this finish, it was possible 

 to fuse the enamel directly on the upper surface of plates, to retain 

 corrosion resistant qualities on all other exposed surfaces, and to reduce 

 the number of process operations. A number plate of greatly improved 

 appearance and durability also resulted. In addition, the curved 



^L. McLaughlin Patent 2,030,999, "Ink," February 18, 1936. 



5 L. McLaughlin Patent 1,951,430, "Printing Apparatus," March 20, 1934. 



« W. J. Scott Patent 1,962,751, "Ceramic Coated Articles," June 12, 1934. 



