This is another big question that comes up time and again. There is also a lot of misinformation or misunderstood practices online. Yeseterday we were doing some research for our Natural Colour Club and looking up items being put forward online to give you blue. It was easier for us to find the wrong information than the right stuff and that is concerning. It is also easier to find the wrong techniques for fixing natural dyes than to find solid tried tested and practiced fixing methods.
Using natural dyes in a sustainable and lasting way is not complicated but it does involve some research and trialing on the dyers part. A lot of information has been lost since natural dyes went out of fashion in the late 19th Century, and therefore we are piecing back together the practices. Also expectations of fabric have shifted so far. We often hear it said that for clothes that were worn everyday redyeing to refresh colour would be part of normal practice. Today when an item fades we simple bin it and move on. Lets face it chemically produced dyes also fade so we should not expect natural dyes to last forever.
So how do we 'set' them into or onto the fabric. Well Indigo's do not need any help with this as the process of dyeing the fibre causes the dye to stick to the outside of the fibre or fabric. You build the colour up in layers and it fades by being rubbed off. This is why denim fabric wears in places where they is a lot of friction first. For all other natural dyes you need to create a bond inside the fibre itself to help the dye to bond. For this we use a naturally occuring salt chemical called Alum. We definitely do not use table salt as is suggested by some. The confusion must come from dyers using the terminology salt in reference to Alum, and the fact that alum is used in food production so you could take a leap and think table salt will do just fine. It is used in fixing chemical dyes so we get the thinking behind it - but it just does not work.
There are also many methods of getting alum into the middle of fibre structure to create the environment to fix the dye to. You can submerge fibre and fabric into a water solution and leave it for 6-24 hours, or you can steam it in using a vinegar based solution. We have tried both and find the steaming method produces deeper colours on linen than soaking, but with silk and wool either works well as the fibre structure is different.
The new emerging method is using soya protein as a bond. This works by building up layers of soya protein on the top of fibre or fabric and then the dye bonds with this. The only issue is that you may struggle to achieve deep reds with madder and richer colours as the use of alum helps to brighten colours - is this due to the fact that alum is acidic... we will need to look into that. The other thing that bothers us is the production of soya millk in the first place. It is grown as a mono crop in large areas that take chemicals and a lot of water. Is this the right use of our planets resources for a fabric production when we have enough alum for it to have no impact upon the environment at all. As sustainability is the core of everything we do we as a team feel soya bonding is not the way we want to produce our items, but you need to decide for yourselves.
If you want to learn more do start with this amazing blog post by Catharine Ellis here