Procion H dye is very similar to Procion MX dye, except that it is far less reactive. The bond between dye and fiber does not form as easily. This means that it takes a lot more heat to get the reaction between the dye and the fiber to go. Steaming is one way to get the necessary energy for the reaction. To compare the two types of Procion dyes: the ideal temperature for the reaction of Procion MX dye with fiber is about 30°C (86°F), but it works pretty well at temperatures as low as 21°C (70°F); the ideal temperature for the reaction of Procion H dye with fiber is about 80°C (175°F), but again slightly lower temperatures will work if you give the dye reactions plenty of time. I have seen recipes for fixing Procion H dye to fiber at room temperature, but a higher temperature is important if you want to get the full intensity of the colors.
Thanks for the detailed info. Couple of questions: you mentioned soda ash as a Procion H fixative, and I've always heard that it HAD to be fixed with steam, is this why the hot water is required? (I've never liked how hot water changes the hand of the silk and shrinks it, and then trying to recover the suppleness with fabric softener). Is there any other method of setting Pro H?
You can actually use [url=http://www.pburch.net/dyeing/reactivedyesprotein.shtml]Procion dyes as acid dyes[/url] if you use vinegar instead of soda ash, and heat or steam or microwave the dye on the fiber. It should not matter whether you use Procion MX or Procion H dyes in those recipes, since the portion of the two types of dyes that can act as an acid dye is very similar. I think that 'real' acid dyes are a bit better for this purpose, but if you already have the Procion dyes, it's handy to try them with vinegar, just to compare the hand of the dyed fabric, or when you need an acid dye in a hurry. There are room temperature 'batching' recipes out there for use with Procion dyes and vinegar, or with acid dyes, but I think it's always best to give the acid dyeing recipes at least a little heat.
If you only do it once in a while, it has no effect. For high-volume use, as in a business, there might be a problem with a septic tank, and constant, frequent dyeing might shorten the life of a washing machine, but I've had no problems at all with occasional use and the municipal sewer.
Is it really ok to consider dumping 10 or more pounds of salt into the washing machine? Are there no ill effects, like corrosion or septic issues?
Acid dye is a little bit nicer and is certainly worth trying. I personally tend to use Procion MX dye most of the time so that I don't have to mess with adding heat, or Remazol type fiber reactive dye (Jacquard Red Label) so that I don't have to mess with dye powders. This is on cotton or silk. With the Red Label dyes, I like to use just a short period of microwaving to make sure that my dye reaction temperature is high enough (I microwave wet fabric that is tightly covered with plastic wrap, and watch closely so the plastic does not blow off), but I don't steam it properly, although I should point out that steaming is recommended for silk painting with Jacquard Red Label Silk Colors.
So is acid dye your final answer, all things considered (price, ease of use, the way the silk is affected, predictable results) for dyeing silk?
I think that Procion MX is the best dye for a silk-cellulose blend, but Procion H is fine, too, if you're willing to provide the necessary heat.
What would the best dye be for dyeing a silk-cellulose (rayon, bamboo, tencel, ect) blend?