Glossary P

Parchment

Printed material, such as a book or document, that is made from the skin of a lamb, sheep, goat, young calf, or other animal.   It was used extensively before the widespread use of paper.   Since parchment manufacture required much labor, its printed matter was very expensive.   A more finely manufactured leather is called vellum .   Vellum is whiter and clearer than parchment.   It requires more effort to make and therefore is even more expensive.

Pigment

A material that colors other materials.   Pigments are natural and synthetic organic and inorganic.   The cells of organisms contain pigments that color skin, eyes, fur, hair and organs.   Organisms that have deficient pigmentation are called albinos.   Pigments are used to color paint, ink, plastic, fabric and other materials.   A pigment is a dry colorant, usually an insoluble powder, in contrast to a dye, which is either a liquid or soluble.   However, there is no well-defined dividing line between pigments and dyes, and some coloring materials are used as both pigments and dyes.   In some cases, a pigment is made by precipitating a soluble dye with a metallic salt.   The resulting pigment is called a "lake". ^{Wiki n.p.}

Polymer

A polymer is a repeating chain of molecules formed by the bonding of smaller, identical molecules called monomers.   Most useful polymers are organic (e.g., cellulose, sugar, starch, glycogen) , based on carbon chains, but there are also many useful inorganic polymers, such as silicones (polysiloxanes), which are long chains based on silicon and oxygen.   Polymers include a large, diverse group of molecules, (e.g. proteins, rubber, kevlar).   Some polymers are crystalline (molecules are ordered) and stiff in one direction, which makes them make good fibers (e.g., nylon); others are amorphous (molecules are random) like silicones, which makes them soft and flexible (e.g., lubricants).

Monomers become polymers by a chemical reaction called condensation.   Polymers are broken into smaller units, including monomers, by a chemical reaction called hydrolysis.   These chemical reactions usually require an enzyme.