Ghost tagging: T he appearance of a faint image impression in addition to the normal inked impression. This is caused by mis-registration of the phosphor tagging in relation to the ink. Sometimes, a plate number impression will have an entirely different number from the ink plate, giving the impression of an error: one dark (normal) number and one light (ghost) number.
Glassine: A thin, semitransparent paper that is moderately resistant to the passage of air and moisture. Envelopes made of glassine are commonly used for temporary stamp storage. Glassine is also used in the manufacture of stamp hinges.
Goldbeater’s skin: A thin, tough, translucent paper. The 1886 issue of Prussia was printed in reverse on goldbeater’s skin, with the gum applied over the printing. These stamps are brittle and virtually impossible to remove from the paper to which they are affixed.
Granite paper: A paper with small colored fibers added when the paper is made. This paper is used as a deterrent against forgery.
Gravure: A printing process utilizing an intaglio printing plate created by photographic and chemical means, rather than by hand engraving.
Grill: A pattern of parallel lines (or dots at the points where lines would cross) forming a grid. A grill is usually: 1) the impressed breaks added to stamps as a security measure (United States issues of 1867-71 and Peru issues of 1874-79); or 2) a grill-like canceling device used on various 19th-century issues.
Gum: The mucilage applied to the backs of adhesive postage stamps, revenue stamps or envelope flaps. Gum is an area of concern for stamp collectors. It may crack and harm the paper of the stamp itself. It may stain or adhere to other stamps or album pages under certain climatic conditions. Many collectors are willing to pay extra for 19th- and some 20th-century stamps with intact, undisturbed original gum.
Gutter: The selvage separating panes on a sheet of stamps. The gutter is usually discarded during processing. The gutter may be unprinted, or bear plate numbers, accounting or control numbers, advertising or other words or markings.