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Unexpected and undesired color changes in paper materials following the use of anoxic treatments for killing insects that infest collections have been reported. This observation and attendant concerns prompted this research. This study examined the influence of a nitrogen gas purge and oxygen scavengers on color stability of dyed textiles in the presence and absence of light. Earlier studies showed that while most dyed textiles exhibit less fading and color change when oxygen is removed from the atmosphere via a nitrogen purge, a small number of dyes exhibit greater amounts of fading and color change in the presence of a reduced-oxygen atmosphere. However, it was unclear whether the earlier reports of increased fading observed in reduced-oxygen atmospheres were due to the presence of light or the absence of oxygen because none of the earlier studies included anoxic treatments conducted both in the presence and absence of light.
In recent years oxygen scavengers have been increasingly used for anoxic pest control measures. These scavengers are known to function through an exothermic reaction. Therefore, this study included a fabric colored with a temperature sensitive dye in an attempt to determine whether the heat generated by oxygen scavengers was responsible for observed color changes in some dyed materials rather than the low-oxygen atmosphere.
Selected fabrics dyed with natural dyes (turmeric and fustic on wool) and synthetic dyes (indigoid and acid dyes on wool, a disperse dye on polyester; and fluorescent dyes on cotton) were enclosed in transparent film packages, treated with one of three reduced-oxygen atmospheres (nitrogen purge, nitrogen purge plus oxygen scavenger, or oxygen scavenger alone), or ambient air (control), and exposed to continuous fluorescent light (320 lux) or total darkness for 90 days. Gas chromatogra- phy was used to verify that no measurable oxygen was present in the reduced-oxygen packages initially and that less than 2% oxygen was present in the reduced-oxygen packages after 90 days. At the end of the exposure period, color change was evaluated instrumentally using a spectrocolorimeter. If specimens exhibited significant color change according to instrumental color measurements, visual evaluations were completed to determine whether or not the changes were visually perceptible
. Results showed that oxygen scavengers did not affect the color of any of the dyes included in this study, including a temperature-sensitive disperse dye. This provides additional experimental findings in support of their safety for use in anoxic pest control treatments. Results also showed that the low-oxygen atmospheres examined in this study provided some level of protection against fading and color change for most, but not all, dyes. One fluorescent dye in the presence of continuous light exhibited significantly more color change in low-oxygen atmospheres than in ambient air. In the absence of light, the same fluorescent dye did not exhibit greater color change in the low-oxygen atmosphere than in ambient air. This suggests that the reaction is photochemical in nature and that the unwanted color change may be avoided during anoxic treatments by conducting anoxic pest control treatments in the dark.