Heather Hopkins, Katrin Kania
The Pompeii dyeing experiment was repeated once more during the Forum 2018 by Heather Hopkins and Chris Hopkins Pepper. During the experiment, wool yarns plus some wool fabric was dyed. The wool fabrics were then submitted to a lightfastness test to see if the different kettle metals may have an influence on the lightfastness as well as on the colour outcome.
For the lightfastness tests, a strip of each dyed wool fabric sample was attached to a cardboard backing, then half of it was covered with cardboard. All samples were exposed to sunlight in a south-facing window in South Germany, starting on March 20, 2019. To have an absolute value of lightfastness, a Blue Wool Scale was exposed together with the samples.
Light fading of the dyes was already discernible after 8 days of very sunny weather; the corresponding strip on the Blue Wool Scale was No.3, classifying the dye as "fugitive", with fading after about 3.6 megalux hours. (This corresponds to about 4.5 years for the start of noticeable fading with average indirect indoor lighting of 120 to 180 lux for an average of 12 hours a day.) There was no difference discernible between the samples in contact with the different metals; fading seems to be the same for all of them.
In case differences in fading speed might become more obvious with more pronounced fading, the samples were replaced in the window for more exposure. A second check after six more days (14 days of exposure) showed the same result - fading corresponding to the rate of the Blue Wool Stripe No.3, and uniform fading across all the samples. They were replaced in the window once more.
The image shows the strips after 14 days of exposure.