| Joan - I would not consider the black light as very useful for dating fabrics. It is normally the dyes and optical brighteners in the fibers that are fluorescing. Many natural substances and some natural and synthetic dyes fluoresce to a certain extent. Synthetic fluorescent dyes were introduced in the 1870's - though they were not immediately applied to textiles. Blankophor, an optical brightener, was introduced in l941 in washing detergents. There are many different types of optical brighteners used today in the finishing of textile yarns - and especially in detergents and bleaches. Optical brighteners are dyes that absorb invisible UV light and radiate it back as blue light. If historic cellulosic textiles have been washed since the 1940's, they might fluoresce noticeably under UV light - even if the textiles are thousands of years old (as I have witnessed). The effect may weaken over time as some brighteners break down, but products from the last thirty years can still produce remarkably strong fluorescence. Many non-Western, village-based cultures do not always use detergents with optical brighteners. In such cultures, the older ethnographic textiles do not fluoresce and the new ethnographic textiles do not fluoresce either. The primary efficacy of comparing textiles in UV, visible and infrared light is to help identify variations in color that might point to restorations - both legitimate and illegitimate. Colors that appear the same in visible light might be the result of combinations of different spectral wavelengths, if they are from different dyeings - thus there would be a divergence of color when the wavelength of the light source is changed. However, in my experience, such variations can usually be detected without resorting to this procedure - though this enhancement is useful when creating photodocumentation. I hope this helps, David Walker office@xxxxxxxxxxxxxxxxxxxxxxx Walker Textile Conservation, LLC. 369 Montezuma Ave. #592 Santa Fe, NM 87501, USA ph: 1-505-474-4905 fax: 1-505-473-0257 |