Abstract

TIM PADFIELD and SHEILA LANDI Veg table dyes melloH 1110dern ones tend to Jade.' (quot d in The Timcs, Sept. 7, 1966) Receiv'd 1/11/66 B TRACT METHODS OF TE TI LIGHT-FASTNESS I FORMATION on the light-fastn ss of natural d es is reviewed. New tests on the fastness of The first systell1atic tests of th light-fastn 55 veral dyes in fluorescent la1np light ar of dyes were 1nade by Dufay [I] about 1733. r ported. The novelty of his nlethod was that it pre- Nearly all natural dyes have a light-fastness vented the inconstancy of daylight fro1n blow BS grade 5. Most hav a fastness below affecting the results of tests nlad at differ nt 4. Nearly all natural dyes will fade badly tin1.es and places. He used as the unit of during an .i posure to 50 n1.illion lu hours of exposure the tin1.e taken for a standard dyeing rtificial light, or to a l11.uch sl11.aller dose of to fade to a specified colour. This standard was daylight. In nlany 111useUll1 displays serious always exposed beside th specinlen und r ading of 1110Stdyes would occur in less than test. These fading e perinlents w re part of an