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Blotting paper, sometimes called bibulous paper, is a highly absorbent type of paper or other material. It is used to absorb an excess of liquid substances (such as ink or oil) from the surface of writing paper or objects. Blotting paper referred to as bibulous paper is mainly used in microscopy to remove excess liquids from the slide before viewing. Blotting paper has also been sold as a cosmetic to aid in the removal of skin oils and makeup.
Blotting paper is made from different materials of varying thickness, softness, etc. depending on the application. It is often made of cotton and manufactured on special paper machines. Blotting paper is reputed to be first referred to in the English language in the 15th century but there is a tradition in Norfolk, England that it was invented by accident at Lyng Mill on the River Wensum.
A form of blotter paper commonly known as watercolor paper is produced for its absorbent qualities, allowing much better absorption of water and pigments than standard art or drawing papers. Although usually categorized as separate from blotting paper, differences in the constituents and thickness of blotting paper and watercolor paper are subtle, and making a distinction between the two is unnecessary as the production process is nearly identical.
Blotting paper is used in chemical analyses as stationary phase in thin-layer chromatography. Blotting paper is also used in pool/spa maintenance to measure pH balance. Small squares of blotting paper attached to disposable plastic strips are impregnated with pH sensitive compounds usually extracted from lichens, especially Roccella tinctoria. These strips are used similarly to litmus strips, however filter paper is usually used for litmus strips, generally to allow for the property of diffusion.
Drugs active in microgram range, most notably LSD, are distributed on blotting paper. A liquid solution of the drug is applied to the blotting paper, which commonly is perforated into individual doses and artfully decorated also known as blotter art. Vanity blotter is blotter art that hasn't been exposed to LSD and is usually sold as a collectible, although inevitably much of this art ends up in illegal distribution. The artwork is printed onto blotter paper and then sometimes perforated into tiny squares or "tabs" which can be torn or cut apart. Most blotter art designs have grid lines as part of the design to either aid in perforation or to be left as a cutting grid. Plain white LSD blotter without artwork is commonly referred to as WoW (White on White) and is usually not perforated but rather gridded with a pen and sometimes laid on commonly obtained watercolor paper.
When used to remove ink from writings, the writing may appear in reverse on the surface of the blotting paper, a phenomenon which has been used as a plot device in a number of detective stories, such as in the Sherlock Holmes story The Adventure of the Missing Three-Quarter.
- Erowid. "Erowid LSD (Acid) Vault : Blotter Art Examples". The Vaults of Erowid. Retrieved December 7, 2013.
- Doyle, Sir Arthur Conan (1905). CHAPTER XI: “THE ADVENTURE OF THE MISSING THREE-QUARTER”. "The Return of Sherlock Holmes". Lit2Go (London: Georges Newnes, Ltd). Retrieved December 7, 2013.