This is a continuation of part 2 on the use mordants in natural dyeing. In this part I am focusing the use chrome and copper. Part 1 of the post on the use of mordants like alum, iron and tin are here Mordant in natural dyeing (part 1)
It is normally used to sadden the colour turning blue to green. Use after bath mordant with alum so as to adjust the colour to ones liking. It can also be use as pre bath which is before the fabric goes in the dye bath. By using with citric acid it will increase in uptake of dye. It does not make protein fibres feel more harsh like iron.
Again it creates sulfuric acid when heated with water. So always heat in well ventilated area and lid. Always use gloves and use utensils when handling cooper.
The colours create with cooper are less light fast compare to alum. Meaning the colour fade less when wash and rinse.
It is tends to add a golden hue to the colour and tends to be quite colour fast. It will cause too much harshness to protein fibres.
Chrome is quite toxic as it can cause dermatitis and carcinogenic. However, it is still not very clear how carcinogenic it is and it’s use on synthetic dyes today. I would just it with caution, like one does with synthetic dyes. Mask and gloves in an open air environment.
Always pour mordant treated dye bath water into sewer or wastewater that will be treated and not into waterway or storm drain.
Always clean the dye pot (whatever it is made of ceramic, aluminium or other types of metal) properly after using a mineral mordant as one wouldn’t like an explosion to happen the next time you start using the dye pot again wouldn’t you?
There are other types of less harsh mordants around like soy beans, acetic acid and tannins. I would say they are mordants as such but they are auxillaries that can help the uptake of natural dyes.