Knife is the cutting die for

envelope An envelope is a common packaging item, usually made of thin, flat material. It is designed to contain a flat object, such as a letter (message), letter or Greeting card, card. Traditional envelopes are made from sheets of paper cut to one o ...

or wrapper blanks. It is called a ''knife'' rather than a ''die'' because the latter is an object that makes an embossed printed impression of the stamp or indicium on the envelope.''Thorp-Bartels Catalogue of United States Stamped Envelopes'', Century Edition, 1954. Traditionally, a knife would normally be made of forged steel. It was placed on a stack of paper with the sharp edge against the paper. The press head forced the cutting edge all the way through the stack of paper. The cut blanks were removed from the knife and the process was repeated. Not only could it cut out the odd shape of an envelope, but a knife could be used to cut out shapes of airmail stickers or gummed labels in the shape of stars or circles. The variety of shapes a knife could cut would be infinite. In

philately Philately (; ) is the study of postage stamps and postal history. It also refers to the collection and appreciation of stamps and other philatelic products. While closely associated with stamp collecting and the study of postage, it is possibl ...

Thorp ''Thorp'' is a Middle English word for a hamlet or small village. Etymology The name can either come from Old Norse ''þorp'' (also ''thorp''), or from Old English (Anglo-Saxon) ''þrop''. There are many place names in England with the suffi ...

knife numbers were and still are, used to indicate the height, width, shapes, and folds of envelopes generally numbered in the order of their discovery by collectors. The United Postal Stationery Societybr>(UPSS)
now has its own numbering system for envelope knives which is seeing more current use.Mintz, Allen, Ed.; ''Catalog of the 19th Century Stamped Envelopes, Wrappers, Cut Squares and Full Corners of the United States''; UPSS, 2001. Undersander, Dan, Ed.; ''Catalog of the 20th and 21st Century Stamped Envelopes and Wrappers of the United States'', Third Edition, UPSS, 2011. .

References

{{Reflist Philatelic terminology Stationery Postal stationery Envelopes