Most of the time Gail dyes fibers that come from animals (sheep, goats, cashmere); protein fibers. There are different dyes for animal fibers vs. plant fibers (cotton, linen, tencel).
She uses Acid Dyes (sounds really scary, Acid) but the acid can be white vinegar from your kitchen.
Gail starts with a skein of yarn that has been soaked in a solution of 1 part vinegar to 3 parts room temperature water. The yarn needs to be in this solution long enough to be totally wet, at least 30 minutes. While this is soaking, the dyes are put into solution.
Using any type of Acid dye, she takes 1 teaspoon of the dye powder, carefully places it in a container, and makes a paste by adding a small amount of room temperature water. Once this paste is mixed around, then boiling water is added up to the 1 cup measurement. This is the dyestock solution. It can be diluted to achieve a paler shade if desired.
The dye stock can be applied to the yarn in several ways.