Isabella Whitworth

probably more than natural and synthetic dyes, wax, resists, and history

Calculating cochineal: using Lanzarote dyestuff

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The historical dye research Jane Deane and I are working on at Leewood (see previous post) involves comparing ‘like with like’. For the initial weld research we used a stock solution of weld extract and divided it equally into five separate jars to dye samples of five fleece types.

Last year I undertook a dye costing with a stock solution. It was for a Somerset-based company called The Woolly Shepherd which promotes the sustainable use of wool, particularly waste fleece that would normally be thrown away. It is producing  needle-felted insulation materials, horticultural products and acoustic panels and also sells a range of small items such as wine coolers and phone covers.

The Woolly Shepherd’s felt is a darkish grey overall, being a mixture of several fleece colours and thus far they had sold all their products undyed. The company asked me to find out if its felt could be natural-dyed to achieve a certain shade of dark pink. It had obtained a sample dyed pink with synthetic dyes and I offered to try to match it as nearly as possible using cochineal, and in such a way that a costing for natural dyes plus the dyeing process could be calculated.

Dye calculations are normally made on percentage of dyestuff to fibre, yarn or fabric, so I needed to work with a known weight of dry felt and a known weight of cochineal. By increasing the amount of measured dyestuff in a sequence of individual vats, I planned to dye a set of samples to calculate a percentage weight of dye to weight of felt. Cutting a precise weight of thick felt has ‘pound of flesh’ Merchant of Venice connotations. It isn’t as easy as it sounds. In the end I cut a piece that was slightly too heavy and then sliced pieces off the side so that I was working with a 200 g weight. I cut this into four so I could work with 50 g samples.

All the felt was mordanted in alum and cream of tartar. I used 12% alum and 8% cream of tartar – although I normally use less. The wool smelled so strongly of lanolin that I wasn’t sure if it had been sufficiently scoured for dyeing, so I erred on the side of a stronger mordant.

Because working with very small weights of ground cochineal is extremely fiddly I made a stock solution.

I used Lanzarote cochineal for The Woolly Shepherd project. Some time ago I undertook quality tests for the  Asociación Milana, found their cochineal to be excellent and I continue to use it.

I ground 50 g dried cochineal to fine powder and tied it firmly  into a silk gauze bag. This helped prevent cochineal fragments entering the dye and avoided the need to strain the dyestuff. The bag was put into a stainless steel vessel with about 500 ml water and heated to simmer point (80C) for about 10 minutes. The decocted liquor was decanted into a container. Repeats of this process followed until there was hardly any colour coming out of the bag. The series of decoctions made up a stock solution of 50 g cochineal in 4 litres of water.

I calculated that I could draw off the equivalent of 1 g cochineal in each 80 ml of water  – if I kept the solution swirling while decanting so that it would be well-mixed.

The dyeing was fairly straightforward although I had an initial panic with the first sample: it appeared that the dye was not ‘taking’. Was the wool too greasy? But after the first half hour I saw the felt begin to turn pink. I slowly raised the temperature to 80C and held it for an hour, then allowed it to cool and sit overnight before rinsing. The colour was nearly exhausted in the vat after the long soak. I prepared three samples starting with a 4% proportion of dye to fibre and then increasing the percentage. With the felt being grey, the dye was always having to work against the base colour and in the end the percentage of dyestuff required for the dark pink was higher than I anticipated.

In a spirit of pessimistic self-knowledge I noted precise quantities, weights, times and individual calculations in my dye notebook. If my actual calculations were later found to be faulty (not uncommon with my maths), I could still make sense of the dyed samples because the maths could be reworked.

When undertaking my research into orchil I’ve studied historical dye notebooks, invoices, orders and the occasional sniffy nineteenth century letter of complaint. A high standard of colour accuracy was expected of past dyemakers by their clients. My exercise with cochineal gave me a small insight into how consistent results, competitive purchase and selling prices were achieved, using natural materials which can vary in quality.

Then as now, good results would depend on careful note-taking, accurate calculations, rigorously consistent dyeing and efficient retention of standard dyed samples.

The Woolly Shepherd: http://www.woollyshepherd.co.uk/

Asociación Milana http://www.tinamala.com

A version of this article was first published in the Journal for Weavers, Spinners and Dyers, Issue 242, Summer 2012, pp 24 – 25

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