The Chemistry of Paper Preservation: Part 2. The Yellowing of Paper and Conservation Bleaching

Abstract

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).

Smartphone citizen science: can a conservation hypothesis be tested using non specialist technology?

“…The plateau region of yellowing vector Y from 1912 to 1964, may point to a saturation in the yellowing condition possible with this type of paper, we are unaware of saturation being reported in an archive context previously. This factor of colour saturation may be a shortcoming of using yellowing to indicate degradation since further mechanical degradation of newsprint could occur after the point of discoloration saturation is reached [9]. The variability of the values measured at the 4 points in the journal volume indicate that the sampling from the front pages and middle pages may mean that the overall saturation is not complete in each folder.…”

“…At the time of production little attention was paid to the longevity of paper; where the issues of paper deterioration in terms of fragility, hornification and yellowing now are significant [8]. The focus of the work here is on the yellowing of paper which the literature reveals to have a number of causes that are extrinsic and intrinsic [9][10][11][12], The yellowing of paper is seen as a challenge to conservation, where yellowing is synonymous with ageing and often more brittle paper which is especially problematic for archival access, and therefore also is an indicator of deterioration of paper integrity although there is a lack of correlation of discoloration with brittleness.…”

Micro-XRF and FT-IR/ATR analyses of an optically degraded ancient document of the Trieste (Italy) cadastral system (1893): A novel and surprising iron gall ink protective action

“…[19]. For example, the oxidation products (as carboxyl/carboxylate, conjugated and unconjugated carbonyl groups) in a degraded paper [20] can be detected by the presence of absorption bands within the restricted range from 1750 to 1600 cm -1 [21,22].…”

Chemical and Physical Analysis for the Improvement of the Dry Mounting Method for Fragile Documents

“…For a better simulation of the environmental factors and storage characteristics of libraries and archives, we performed our accelerated degradation at 80°C and 65% Relative Humidity (ISO Standard 5630/3) without ultraviolet or daylight lamps. In particular, the selected values of temperature and RH assure that the water content of paper does not change on heating 11 , since the adsorbed water is a key factor in the kinetics and mechanism of paper degradation 12,13 . With ageing, a slight decrease of luminosity L* (TABLE 2) and a progressive yellowing of the laminated surface of Whatman paper were observed, slight in the Paraloid-coated sheets and high in the Neschen sample.…”