Marginal Markings Committee

 

Plate Surface Treatment

 

 

 

 

Design Elements

 

Etched or engraved printing plates receive a great deal of wear, causing loss of image definition and other poor quality reproductions. Eventually, plates would have to be replaced if the production quantity was large. To extend the useful plate life, various methods were tried to enhance the surface hardness.  

 

When all finishing operations have been completed, a plate is hardened, or plated with a metalic protective coating, to lengthen its usefulness.  This insures uniform printing results and a greater number of impressions.

 

Several marginal marks were used to identify the process that had been used on a particular plate. These marks first occurred in 1918 and lasted through 1938, a period of time when the rotary press was becoming used extensively and the plates were used for larger production runs.

 

A.  Letter 'O' - Indicates the plate was quenched in an oil bath .

 

B.  Letter 'F' - Indicates the plate had passed a hardening test and was ready to be used for printing .

 

Various materials were used as plating for the engraved plates to reduce wear.  These designations were used for only a short period of time while the BEP was experimenting with ways to reduce production costs.

In 1926 the Bureau began experimenting with chrome plating to extend plate life.  The chromed surface is very hard and further can be removed and replaced chemically to yield a fresh surface as long as the plating has not worn down to the steel underneath.  This process was first employed on rotary press plates used for coil production, as rechroming was easier than making and curving new plates for the press, and by the summer of 1926 almost all rotary press plates were being chromed.  This process allowed some plates to yield over a million impressions, and later over two million.

 

A.  Letters 'C.S.' - Stands for chrome steel, indicating the plate had been chrome plated.

 

B.  Letter 'C' - Stand from chrome, indicating the plate had been chrome plated.

 

C.  Letters 'E.I. - Stands for electrolytic iron, indicating that the plate had been created through an electrolytic process.

 

 

Plate Identification

 

Production Markings

 

Inscriptions

 

 

 

                                                

SUBJECT REFERENCES

 

James H. Baxter, Printing Postage Stamps by Line Engraving, American Philatelic Society, August 1939, pg. 108-110.