|Curly Wensleydale wool dyed using Acid dyes|
If you are painting or printing with Acid dyes, or using Procion MX dyes as an acid dye, and wish to steam or microwave set the dyes, the fabric should first be pre-soaked in a solution of Citric Acid and allowed to dry before painting.
The term “acid” in Acid dyes refers to the relative pH balance of the dye bath. The pH is dependant on the concentration of the acid in water, which in turn depends on the actual volume of water. The level of pH is measured on a scale of 0 to 14 with 0 representing the highest concentration of acid and 14 representative of the most alkaline.
0.5% by weight of Citric Acid (i.e. 5g in 1 litre of dye bath water, or 25g = 1oz in 5 litres = 1 gallon approx) gives a pH of 4.0. This is in line for Levelling Acid Dyes (the family of acid dyes sold by George Weil) where the recommended pH is around 4.0, and this acidity also works well for the other acid dye families, Milling and pre-Metallized.
As always this assumes that the water in the dye bath started at pH 7.0, which it may not, so testing with universal litmus paper is strongly recommended to ensure the correct acidity. This is equally true when using vinegar.
The post "Chemistry of Textiles and Dyes: pH" on Chemistry Art Blog explains further how the pH effects dyes.
View the range of Acid dyes on the George Weil website.