A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Ultraviolet Light
A wavelength of the electromagnetic spectrum that takes the form of light beyond human perception. It is very energetic, and with larger photons than in the visual spectrum, ultraviolet light can more easily break chemical bonds. This damage causes some colorants to fade, especially dyes which have smaller thus weaker molecular structures. It can also cause the small molecules in dyes to become very reactive, creating the effects of fluorescent colors or optical brighteners.

Undivided Back
Generally refers to all forms of postcards printed before March 3rd, 1907 when postal regulations reserved a card’s entire back for the mailing address and postage. It can also specifically refer to postcards within the same period, but were printed after December 24th, 1901, when postal regulations ended the use of private mailing cards. These were the first privately printed cards that were authorized to use the words Post Card.

Universal Postal Union
An international organization formed in 1874 as the General Postal Union to provide uniform regulations for the mailing of letters and cards between its members. Prior to the Union every country had to make an individual treaty with each other nation to regulate international mail. It changed its name to the Universal Postal Union in 1878, and became a special agency within the United Nations in 1948. All but a handful of nations belong to it today.

Uranotypie (Oranotypie)
A trade name for a type of glossy real photo postcard published by the New Photographic Society in Berlin at the beginning of the 20th century. These cards are hand colored with gilding.

Uvachrom
A subtractive mordant dye tone process for the printing of color photographs, patented by Arhur Traube in 1916. It required multiple transparencies making it a difficult and expensive process so it never gained widespread commercial use. This method was used it to produce color postcards published under the Uvachrom name, and book illustrations for the Union of Color Photography (Farbwenphotographie).