n.a complex polymer that when left in groundwood pulp leads to the embrittlement of the paper created from such pulpMinogue 1945, 116Straw, wood pulps, and other fibers of no commercial value today were frequently used as adulerants in the rag papers or were used alone in the very cheap papers. The need for and the means of purifying these fibers for paper-making were not well understood and the papers were made with most of the naturally occurring acids and lignins intact. The presence of these foreign substances has been largely responsible for the obviously poor quality and the accelerated deterioration of some of the papers dating from the latter half of the nineteenth century.Poole 1977, 165Groundwood pulp contains lignins, complex organic compounds which decompose to form a number of components some of which are acid. In turn, these components cause darkening and embrittlement of the paper.Clark 1978, 15When exposed to the ultraviolet ray present in sunlight or fluorescent light, paper bleaches and its inks fade, the residual lignins remaining from the paper-making process react with other compounds to yellow the paper, and eventually the cellulose fibers in the paper weaken and break.Burgess and Goltz 1994, 185–186Fibre strength and durability is very dependent on the length and state of degradation of the cellulose molecules; lignin contributes significantly less to the strength of the paper sheet.Hackbart-Dean and Montgomery 1998, 76Adequate supplies include proper storage containers, such as lignin-free or low lignin boxes and folders, chemically stable plastic or paper enclosures, microspatulas, brushes, and bond paper for preservation photocopying.Ritzenthaler 2010, 46Besides cellulose, plant fibers contain sugars starches, carbohydrates, and lignin (the noncarbohydrate, nonfibrous substance in the cell walls of living plants that is responsible for their strength and rigidity but that in paper contributes to its degradation).Ritzenthaler 2010, 51–52Wood is the primary source of cellulose fiber for paper being produced today. Depending on species, wood consist of approximately 45 percent cellulose, 20 to 25 percent hemicelluloses, 16 to 34 percent lignin, and less than 5 percent other substances Groundwood pulp, which, as its name implies, is produced by mechanically grinding or macerating wood into separate fibers, does not produce stable paper. After the bark is removed, logs are ground on a revolving stone. The resulting pulp retains all of the components of wood, except for water-soluble materials, which wash away during the grinding process. The fibers are short, and a large amount of lignin (which is unstable, light-sensitive, and breaks down into acid compounds as it ages) is retained.Ritzenthaler 2010, 52While ground wood paper is always unstable, it is possible to obtain relatively strong, high-quality paper from wood pulp that has been chemically treated to remove as much of the lignin and other noncellulosic material as possible.Ritzenthaler 2010, 185The issue of lignin content can be somewhat confusing, especially because a number of suppliers claim to offer paper and paperboard enclosures that contain no lignin. It is more accurate to state that materials of a specified quality are low in lignin content, as it is difficult to detect low levels of lignin (below 7 percent) using the standard spot test (i.e., phloroglucinol).