‘Should I scour the vegetable fibres that I am going to dye with indigo?’ This was the jist of a very sensible question I was asked prior to running an indigo dyeing workshop.
My gut reaction was to say of course it is better to scour. If the question had been asked of wool or another protein fibre such as silk I would have said ‘yes’ without really thinking about it. Lanolin remaining in wool is notorious for forming a barrier and resulting in uneven dyeing. However vegetable fibres have a different structure entirely and I decided to do a controlled experiment - or as controlled an experiment as I could manage - before I replied. I have learnt that it is best to check what you read on the internet and more surprisingly in printed books.
So I took hemp and cotton fibres from the same sources that I had used for a the meadowsweet dyeing experiment. I was pretty sure that the improved uptake of the meadowsweet dye was in part due to the more vigorous scouring the fibres received.
So 2 sets of yarns (hemp and cotton) were prepared:
Set one - to be scoured with washing soda at 100% dry mass of fibre by boiling in the solution for 2 hours
Set two - to be rubbed in a warm washing up solution for 5 minutes to ‘wet’ them.
After this treatment they were rinsed and dipped for one minute in an Indigo bath before being ‘swung’ outside in the air and rinsed as I would normally do and hung up to dry fully.
These are the results:
Reading from the top: hemp not scoured, hemp scoured, cotton not scoured, cotton scoured
2 hours of scouring made no difference whatsoever in the uptake or (initial fastness with indigo).
Of course I do not know how the fibres had been treated before they got to me. But what I do know is how much better they reacted with meadowsweet dye when they had received the more vigorous scouring.
NB Further experiments are being undertaken on the effectiveness of the scouring method with vegetable fibres and non indigo natural dyes.