Contributors: Amy Morse
Light fastness refers to the degree of resistance to photo-degradation a pigment has on exposure to ultra-violet light and infrared radiation. Pigments in materials are diminished during exposure to these types of light sources and this process is referred to as photo-degradation (Library of Congress, 2010). These materials can range from textiles to bone.
Synonyms in English
|French||Résistance à la lumière|
|Spanish||Solidez a la luz|
|Portuguese||Resistência à luz|
|Italian||Solidità alla luce|
The first recorded experiments testing for degrees of lightfastness that are known were made in the 18th century by Dufay (Padfield and Landi 1966, 181).
An object that has light fastness or is lightfast, exhibits minimal photo-degradation of its incorporated pigments on exposure to radiant energy or varying forms of light (Bowman 1983, 36). It is not possible to prevent the loss of pigment completely (Padfield and Landi 1966, 181). Fading is a complex chemical reaction and therefore treatments to enhance light fastness cannot make a material completely immune to fading (Johnston-Feller et al. 1984, 114).
Different types of dyes have varying sensitivities to light exposure and are therefore less lightfast. For instance, studies have shown that natural or vegetation based dyes are more prone to “mellowing” versus the reaction of synthetic colors which “fade” (Padfield and Landi 1966, 181). Nevertheless, the mid-1800s, natural dyes were starting to be replaced by synthetic dyes, which can exhibit a full range of degrees of light fastness from fading very quickly to very stable lifespans (Cristea 2006, 238).
Bowman, J. G. and B. M. Reagan. 1983. Filtered and Unfiltered Lights and Their Effects on Selected Dyed Textiles. Studies in Conservation 28(1): 36.
Cristea, D. and G. Vilarem. 2006. Improving Light Fastness of Natural Dyes on Cotton Yarn. Dyes and Pigments 70(2006): 238.
Johnston-Feller, R., R. L. Feller, C. W. Bailie and M. Curran. 1984. The Kinetics of Fading: Opaque Paint Films Pigmented with Alzarin Lake and Titanium Dioxide. Journal of the American Institute for Conservation 23(2).
Library of Congress. 2010. Everyday Mysteries: Fun Science Facts from the Library of Congress. http://www.loc.gov/rr/scitech/mysteries/colors.html.
Padfield, T. and S. Landi. 1966. The Light-Fastness of Natural Dyes. Studies in Conservation 11(4).