Nuuchaahnulth ceremonial curtain, before treatment

Detail of curtain, after treatment

Like many other industries, textiles are going green these days. Natural dyes are enjoying a resurgence because of their sustainability and relative non-toxicity. For a recent textile conservation project I decided to use natural dyes to get “just that right colour” to repair some major losses in a First Nation Nuuchaanulth ceremonial curtain which was displayed at the Morris and Helen Belkin Art Gallery earlier this year.*

As can be seen in the photographs, the ground fabric of the curtain is discoloured and stained, with large losses. One of the advantages of custom dyeing is that the dirty-cotton colour so often needed to match historic textiles is just about impossible to find in fabric stores. “Dirty linen” is not a popular shade. Fortunately for me, the Canadian Association for Conservation had sponsored a natural dye workshop at Vancouver’s Maiwa Handprints last year, which I attended. Now was the time to put my new skills to the test.

Dyes do not bind well to cellulose fabrics like cotton and linen, so the first step in the process was mordanting. Mordants, from the Latin “to bite,” are chemicals that allow dyes to attach to cellulose. The mordant binds to the cellulose, and the dye binds to the mordant. Tannic acid is the mordant which attaches best to cellulose and is always the first to be applied. Other mordants, such as alum or ferrous sulphate (iron) can be applied afterwards to expand the colour palette: tannic acid gives an overall yellow tone to the fabric, alum brightens colour and iron dulls it.

All of this means that a single dyestuff can yield many colour variations, making it possible to zero in on a particular shade if one is willing to run a lot of tests. I began by making two large test swatches: cotton mordanted with tannin followed by alum, and cotton mordanted with tannin, followed by alum, then by iron. I made a series of test dye baths using materials I thought would give good “yellowy-beige” colours, including calendula, black oak, coffee, osage orange and cutch. Black oak top dyed with cutch, on a tannin-alum-iron mordant base, gave just about the right colour. I dyed a large batch of fabric using the test results as a guideline, and came up with a very satisfying match. This was rinsed well, dried, ironed and used to make underlay fills for the areas of loss, stitching the edges in place with a very fine polyester thread.

One concern with using natural dyes in conservation is light stability. The textile industry is also concerned with this, and has found that antioxidants improve light fastness. Tannic acid is an excellent antioxidant, but the textile industry is putting their money on ascorbic acid – good old vitamin C. Improving light fastness is a worthy goal, but one can also look at light sensitivity as a good thing: naturally dyed infill fabrics act as canaries in a coal mine. If the infill fabric fades perceptibly, then the historic textile is being exposed to too much light.

*See backstory: Nuuchaanulth Ceremonial Curtains, February/March 2010 issue.

Previously: A relocation project
Next issue: Organization: the first step towards preservation