Stamps and Envelope

Fluorescence in philately (stamp collecting) is a recognised dimension to the appearance of some stamps and helps with identification and verification of postage. On this envelope there are two stamps. The one on the left as you look at it, fluoresces a greenish-yellow under ultraviolet light. There are also post-markings running along the lower portion of this envelope that have been printed by the postal authorities in orange fluorescent ink. The combination of vertical lines of varying heights and groupings impart information (rather like a barcode on a tin of baked beans) that tells of the date, time and location of the letter's posting. The use of fluorescent inks allow the marks to be read clearly by a machine under ultraviolet light and not confused with other markings that may be on the envelope.