For several years a collection of my naturally-dyed samples has been held at The Royal Institute for Cultural Heritage (www.kikirpa.be) in Brussels, Belgium. This centre covers all aspects of Belgium’s artistic heritage and its laboratories carry out work on conservation techniques and materials, including the analysis of dyes on textiles from all periods and from all over the world. My samples are sometimes used in this analysis work, mainly for purposes of comparison.
Every now and then I receive a request for further samples and a few weeks ago I was asked for some more rhubarb samples, in addition to the ones they already have. The samples requested were to show the pinks and greys available from rhubarb root when the colour is extracted in an alkaline solution, using either washing soda or household ammonia.
As I couldn’t readily locate any suitable samples, I decided to produce some. I first soaked the chopped rhubarb root overnight in a solution of water and washing soda. By this time the liquid was deep red in colour and I added two alum-mordanted samples and two unmordanted samples. I left the samples to soak for about 24 hours, then I removed them. I dried one pair of samples away from the light and the other pair of samples was dried outdoors in direct sunlight. The samples exposed to the light dried to a greyish shade through a process known as photo-oxidisation.
The photo below shows the colours.
The upper two samples are alum-mordanted and the lower two are unmordanted. The pink samples were dried away from direct light and the greyish ones were dried outdoors in sunlight.