If you want to dye cotton thread at the same time as silk, you cannot use acid as the auxiliary chemical. You have to use soda ash (or some other high-pH chemical) to dye cotton with fiber reactive dyes. Fortunately, the silk will dye perfectly well under the same circumstances as cotton, though it may become a little softer and a little bit less shiny. However, the premixed colors will come out more different on silk and cotton when used with soda ash than when used with vinegar or citric acid.
To get silk and cotton to dye the same color at the same time with Procion MX dyes, avoid using mixtures of colors, such as the zillion-and-one different premixed colors sold by most dyesellers. Stick to the unmixed single-hue Procion MX dyes, which are listed on my chart,
Which Procion MX colors are pure, and which mixtures?.
You can combine these pure unmixed dye colors in LWI (see
How to Do Low Water Immersion Dyeing), dyeing silk and cotton at the same time, and still get a good match. Here's a link to an old post at the Dye Forum on my site showing a rayon dress and a silk purse that I dyed to match in the same LWI dyebath:
silk and rayon, dyed to match.
Paula
