Graphite Lines Vertical graphite lines printed in black (beneath the gum) of certain British stamps in 1957 for use with automatic sorting machines.
The use of graphite lines was developed by British Post Office scientists in conjunction with the stamp printers Harrison & Sons of High Wycombe and the stamps were first used in an experimental machine at Southampton.
Naphthadag: a trade name for a composition of Naphtha and Deflocculated Acheson's Graphite, used for graphite lines printed on the back of some British stamps used in connection with automatic sorting experiments, 1957.
Graphite lines - Adhesive stamp bearing one or two vertical lines of black electrically conductive graphite on the back, under the gum.
Gravure - See Photogravure.
The backs of two British 1-penny Queen Elizabeth II stamps showing experimental graphite lines. The stamp at left has the graphite lines misplaced closely together. The stamp at right shows the normal spacing between the graphite lines.
 See also: Stamp, Machin, Used, Cover, Postmark
  
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