For some while I’ve followed the progress of the Bristol Cloth and the businesses at the Bristol Textile Quarter. I also enjoyed attending a natural dyeing workshop held by Botanical Inks. Recently Babs Behan from Botanical Inks has presented a TED Talk on textile dyeing. I have found the talk fascinating and thought that I would share it with you. Being a lover of facts and figures I thought I’d add a few science bits I found from my own research too.
I was really struck, particularly when Babs talks about how dyes are used in relation to jeans. I had, clearly wrongly, always assumed that jeans manufacture had continued to use natural indigo dyes. I think this assumption had been because I know that indigo has a particular property whereby only the surface of the fabric is dyed and inner layers remain uncoloured. This means that as denim ages and gets worn the fabric takes on that faded look so peculiar to denim jeans. Apparently, indigo has been synthetically produced since the end of the nineteenth century and this is what is mostly used in the textile industry .
That said, synthetic indigo and natural indigo dye are chemically exactly the same, however there are some differences that are worth noting . Natural indigo can contain impurities like tannins, which some believe make its colour richer and more interesting. Synthetic indigo uses raw materials such as aniline and hydrogen cyanide which are highly toxic .
Babs also talks about azo dyes, which are typified by a characteristic nitrogen to nitrogen bond (N=N) . Azo dyes constitute 60-70% of the dyes used in the textile industry . Many azo pigments are considered non-toxic, but some are mutagenic, carcinogenic or provoke allergic reactions. The textile industry discharge large quantities of azo dye effluents (up to 15% of the dye is lost this way), with acute hazardous effects on the environment and human health. There is restricted use of azo dyes in textile and leather articles under UK law, however azo dyes can be broken down by skin bacteria into carcinogenic aromatic amines many of which are unregulated .
 Dyes used for denim dyeing
 Synthetic vs natural indigo dye
 Sustainability of indigo in denim production
 Azo dyes
 Use of azo dyes in the textile industry
 Aromatic amines as carcinogens