Gum

Gum is the adhesive on the back of a postage stamp. It lets the stamp be moistened and stuck to an envelope. For collectors of mint stamps, gum is not a trivial detail: whether a stamp has its original gum, whether that gum has been disturbed by a hinge, and what kind of gum it is can all dramatically change a stamp’s value.

Types of Gum

• Gum arabic — a natural resin used on many early stamps; often yellowish or brownish, and can crack with age.
• Dextrin — a starch-based adhesive, used widely and often mixed with other gums.
• PVA (polyvinyl alcohol) — a synthetic gum introduced on many issues from the late 1960s. PVA is often nearly invisible and matte, and is sometimes tinted so it can be distinguished.
• Self-adhesive (pressure-sensitive) gum — used on modern peel-and-stick stamps, applied with a backing paper.

Many catalogues list gum differences as separate varieties when they occur within the same issue.

Gum Condition Terms

• Never hinged (NH) or MNH — undisturbed gum, never mounted with a hinge. See never hinged.
• Lightly hinged (LH) — a small, faint hinge mark.
• Heavily hinged (HH) — noticeable disturbance or hinge remnants. See hinge remnant.
• Disturbed gum — gum marked by fingerprints, heat, humidity or contact with album pages.
• Part gum and no gum — only some gum, or none.
• Regummed — gum added later, usually to deceive.

Gum Problems

Old gum can crack, causing the paper to crease or split. Tropical climates caused toning and “gum staining” on many colonial stamps. Excessive humidity can make gum stick to album pages; heat can make it glossy or bubbly.

Should You Ever Remove Gum?

Some specialists of classic stamps prefer to remove cracked or toned gum to protect the paper, and catalogues often price early stamps “without gum”. For most collectors, however, removing gum from a stamp that still has it reduces value. Never regum a stamp.