The light-fastness of the natural dyes
Information on the light-fastness of natural dyes is reviewed. New tests on the fastness of several dyes in fluorescent lamp light are reported.
Nearly all natural dyes have a light-fastness below BS grade 5. Most have a fastness below 4. Nearly all natural dyes will fade badly during an exposure to 50 million lux hours of artificial light, or to a much smaller dose of daylight. In many museum displays serious fading of most dyes would occur in less than fifty years.
There is no very effective way of reducing the rate of fading. Ultraviolet absorbers over light sources give a worthwhile increase in light-fastness to most, but not all, dyes. Low relative humidity reduces fading. Display in cases filled with an 'inert' gas benefits most dyes but accelerates the fading of some pigments used on fabrics. Valuable textiles whose dyes have a light-fastness below 6 should not be permanently displayed.
The complete article in pdf(1Mb) is a facsimile of the article first published as:
Tim Padfield and Sheila Landi, 'The light-fastness of the natural dyes' Studies in Conservation, volume 11, 1966, 181 -- 196.
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