Friday, 12 January 2018

To Scour or not to Scour? A Galling question....

2018 was off to a good start as soon as I unloaded my van in preparation for the Sturt Summer School. I had a full class of students eager to learn the basics of natural dyeing and then to progress to mordant printing.

One of the most important aspects of all dyeing is the preparation of the cloth beforehand.  All too often we are in such a hurry, we misinterpret 'scouring' to mean "a quick rinse or wash in the washing machine".  Whilst any preparation has to be better than nothing on store-bought fabric, failure to take the time to ensure the fabric is free from grease, oils, dirt and sizing will result in patchy and uneven dyeing, leading to disappointment and waste of time and materials.

Below is a photo of already-whiter-than-white PFP (Prepared for Printing) linen tea-towels that I buy to print on with pigments. The water-based printing emulsion is mixed with concentrated fabric pigments which are screen-printed with a design. Once perfectly dry, the tea-towels are heat-set to bond the resin-based print-paste to the fabric.  It will only ever sit on the surface of the fabric, not inside the fibres as in dyeing.

However, in order to dye these tea-towels (in either natural or synthetic dyes) they must be scoured thoroughly first.  I figured not much would happen but at least I was doing a practical demonstration of the scouring process to the students, most of whom were beginners. 

Was I wrong!! The photo below shows the water that the 5 teatowels were scoured in - can you believe the colour of it - almost looks like a dye itself!!! After this photo was taken I started the process again and scoured the tea-towels a second time. The second lot of scouring water was paler than the first, but not entirely clean.  Given that each scouring should take around 2 hours, we rinsed them and went onto Galling the linen in a Gall Nut soak before we could mordant them the following day. This demonstration clearly shows that whilst the linen tea-towels may be PFP, they are not PFD (Prepared for Dyeing). This is an important distinction if you are buying fabric from a wholesaler to dye with.

Scouring water from the white linen tea-towels
Another important process in fibre preparation for immerse dyeing that is commonly omitted for cotton is the galling or tanning of the fabric or fibre before dyeing. This process literally 'tans' the cloth so that the mordant will attach more readily to the fibre, which in turn attracts the dye. I must admit that I have been a culprit in the past, but Joy Boutrup and Catharine Ellis converted me to galling  cotton when I attended a two week intensive course with them back in 2013. Galling can be done with a number of different plants but I prefer to use the Gall Nut method as it is fairly colourless.

I set up several experiments using store-bought tabby weave cotton fabric;  fabric that had been untreated and unwashed; fabric that had been unwashed, unscoured but mordanted in alum;  fabric that had been scoured and mordanted in alum; fabric that had been scoured and mordanted in Symplocos; and fabric that had been scoured, tanned in Gall Nut and then mordanted in Symplocos. We then dyed the pieces of fabric in a Weld extract dyebath for one hour and observed the differences between them once the samples had been washed, dried and ironed. 

The richest colour and most evenly dyed sample was, not surprisingly, the one that had been scoured, tanned and mordanted in Symplocos.  About one shade behind were the scoured and mordanted samples and the cloth that had been neither washed, scoured nor mordanted was the worst dyed sample of the lot. The differences were easily seen by eye, however did not really show up on camera, hence no photos.

In theory we should also have done a test that included a step with Turkey Red oil for the cotton, but in a 4-day workshop this was unfortunately one step too many!

In my next post I will show some examples of what the student's achieved in the four days, or if you are on Instagram I have posted a few of them @julierydertextiles.

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