Recent;y I have started using natural dyes again. There is a lot written on this subject of using mordant in natural dyes. I have use mordants sometimes I don’t use mordants. It all depends of the property of the natural dye that you are going to use.
I have so far used natural dyes using tumeric, coffee grounds, dahlia and onion skin on cellulose (cotton, linen). They take the dye well without any mordant.
I have used ivy without any mordant and the fibers (protein or cellulose) and they don’t take on dyes too well. Ivy will need some mordant.
Here are three common mordants used in natural dyeing process. Some mordants can be use with one and another in natural dyeing. For example mordant a fibre with alum. Then decide if one one want to ‘sadden’ the colour then use iron during after dye bath.
Alum is easily available anywhere not necessary just from specialist craft and dye suppliers but on ebay as well. As it is use in cooking (anti caking agent, pickling), deodorant and as anti prespirant.
It is a relatively safe compound to use in fabric dyeing. However, when it is heated it can produce sulphuric acidic fumes which can be irritating when inhaled and corrosive. Therefore always try to use aluminium pots instead of stainless steal pots. When heated up always in a well ventilated area like outside and use gloves when handling alum mordants. This due to the reaction of acids in sweat from hands with sulphuric acid. Personally I don’t heat up alum crystals I just use hot tap water and let it dissolve by itself.
Alum itself however has not got much of a colour stay on the cellulose fabrics. I have tried using them and they just wash off as soon they go into a after dye wash with synthrapol. There is one can use alum citrate but using 50: 50 of alum (potassium aluminium sulphate) and sodium acetate.
Commonly use as an after bath in order to change the colour after dyeing. It ‘saddens’ by making turning a vibrant colour into a deeper colour a bit like going from summer to autumn colours. One can use rusty nails instead of going out to buy iron powders. Use in iron as supplements to treat low hemoglobulin levels in the body. High amounts can be toxic. So keep them out of reach especially young children.
Again it does produce sulphuric acid when mixed with water. So wear gloves and use in well ventilated area. Use sparingly as it can be harsh on fibres especially protein fibres. Less is more, rinsing out will do no harm to the fibres.
It is use to give the brightest colour especially on cochineal (scarlet red), bright oranges on madder and purple on logwood. The drawbacks of using tin is that, it not as light fast (resistant to fading and changing colours) as alum. This is with exception of cochineal. Overexposure can damage the fibre (especially protein (wool, silk, cashmere) fibres). Plus it’s not cheap to buy.
Again do take care when handling tin when heated as it’s acidic. In which can cause chemical burns when in contact with skin. Fumes can irritate and it’s corrosive.
Personally I would use the Iron and Tin mordant outdoors then rinse them. Less is more as too much of it will damage the fibres. Always clean them up after use and you don’t want any metal deposits to be still lying around. It can explode is one is using a ceramic made pot as the metal deposits get stuck in the hairline cracks Also have a dedicated utensils just for mordant. Never use them again for cooking.