Yellowing is often viewed as one of the early signs of the aging and deterioration of paper. Depending on the nature of the paper and conditions of storage, the yellow may eventually turn to brown and the paper may become brittle as it reaches the later stages of aging. This discoloration on aging can be attributed to the presence of chromophores found in some of the products formed from the degradation of one or more components of paper (1, 2). While there does not seem to be a correlation between discoloration and loss of mechanical strength (3-7), the yellow color in paper is considered an undesirable characteristic.With the development of new and improved mechanical pulps (8), there has been renewed interest from the pulp and paper industry in the photochemical reactions that accompany the yellowing of paper, particularly in lignin-rich papers such as newsprint. Research has centered around identifying the chromophores that are formed, the reaction mechanisms that cause the lightinduced yellowing of paper, and the possible use of chemical reagents to inhibit these mechanisms (9-15).Paper conservators are also interested in the nature of the discoloration of paper, not only from the aesthetic view that the appearance of the paper can be enhanced, but also from the conservation view that the paper might be stabilized. An understanding of the types of chromophores responsible for yellowing can assist the conservator in making intelligent choices regarding the use of bleaching methods in the treatment of old papers and artifacts. Many bleaching methods are now available and, in fact, conservation bleaching has become an important area of conservation research, second only to mass deacidification (16). This paper will discuss the causes of the yellowing of paper and then focus on the methods used in conservation bleaching.1. The primary chromophores of lignin absorb nearultraviolet light (300-400 nm).

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