Working With Silk
Silk is a protein filament secretion much like hair - rather than a cellulose plant fiber such as cotton. This is also why silk is proportionately much stronger than cotton (and steel).
TrueTieDye's how-to series demonstrates dyeing silk using Procion MX type fiber reactive dyes. While this is one of many possible methods for dyeing silk, it is the best method in terms of color permanence and overall simplicity. However, even if you do happen to use a different type of dye with silk - all of the folding, tying and dye application techniques shown in the DVD's can still be applied.
Remember, you don't have to know any chemistry or technical jargon in order to use the system presented in the how-to videos. But be warned, silk comes from silk worms - so it definitely is not vegan.
The difference between paint and dye
It is also important to distinguish between fabric dyes and fabric paints. Fabric dyes form chemical bonds (which vary depending on the type of dye used) with the fiber (or filament in the case of silk). In contrast, fabric paints merely "adhere" to the surface of fabrics much like paint on a wall. This means that fabric paints generally have less long term durability on fabrics which are frequently washed. In many cases the fabric paint can also be "felt" on the surface of the fabric - whereas dyes have no detectable texture.
What's even more confusing is that decorating silk by hand is often referred to as "silk painting", regardless of whether the artist is actually using paint or dye!
Fabric paints do have another purpose - they're among the only (decent looking) alternatives for decorating polyester and synthetic fabrics which are too complicated and hazardous to dye in a home art studio setting. If you are determined to use fabric paints - the folding, tying and color application methods taught in the video series can still be applied.
Why we recommend Procion MX type dyes for use with silk
Traditionally, the widely practiced methods for dyeing silk involved the use of acid dyes. Acid dyes were invented long before the modern fiber reactive Procion MX type dyes featured in the "learn how-to tie dye" series.
Acid dyes are essentially colored mineral salts which dissolve into negatively charged ions. These ions bond to positively charged sites on the silk and create an ionic bond between the dye molecule(s) and the silk. This ionic bonding is also called hydrogen bonding. As per their name, acid dyes do this best at an acidic pH such as in a vinegar bath.
Procion MX and similar fiber reactive dyes are composed of a more elaborate synthetic molecule which is particularly designed to create a far stronger, more permanent covalent (electron-sharing) bond with the hydroxyl (OH-) group found in cellulose. This reaction is dependent on the highly alkaline (basic) conditions created by soda ash solution.
It is a unique peculiarity of silk that it contains hydroxyl groups. Other protein filaments like wool, mohair and alpaca can only be dyed with acid dyes - Procion dyes will not bond to them since they do not have hydroxyl groups as part of their chemical structure.
Tips for working with silk
Procion dyes look great on silk and they are far more colorfast and permanent than the best acid dyes. However, acid dyes are capable of a substantially different color palette than Procion type dyes due to the differences in their chemical natures. What you don't want to do is mix acid dyes and Procion type dyes in the same reaction.
A given color of Procion type dye will often look markedly different when applied to cotton and silk - meaning that the colors which you obtain on cotton are not an accurate predictor of what the same palette will look like on silk.
When using any Procion type dye with silk, it is important to microwave the dyed item. The heat changes the (microscopic) shape of the silk protein filament, exposing more bonding sites (hydroxyl groups) to the dye - and that translates into more bonded dye and more vibrant color!
Learn more about making tie dye here.