Synthrapol works best with HOT water, yes, HOT water, when washing out excess dye, particularly Fiber Reactive Dye. You are getting out the excess loose dye molecules that have not been chemically bonded to the fabric. This is a good thing! Then you can rest assured that the dye won't bleed on you, or the family underwear, the next time you wash it. Hot water is also best for the pre-washing we discuss below. Acid Dyes for wool and silk are a different story - hot water can actually break the bonds of the acid dye and cause more washout of color than you would want. Wash wools and silks dyed with Acid Dyes in cool to warm water. Synthrapol is great for washing silk and wool also because of its neutral ph. High pH detergents actually can damage silk and wool.
Prewashing in Synthrapol helps remove invisible lubricants, fingerprints, dirt, oil, silk worm gum and other impurities that can interfere with the dye and cause uneven dyeing. It is especially important for tub dyeing where you want an even consistent dye job. Not pre-washing is one of the biggest causes of a "splotchy" result. Even PFD (prepared for dyeing) fabrics, yarns and clothing should be pre-washed! We never recommend skipping this step, especially with all the imported fabrics and clothing these days.
Synthrapol as the afterwash keeps loose dye particles of dye in suspension so they don't stain other areas of the fabric. Also, since Synthrapol is pH neutral, it doesn't encourage loose fiber reactive dye particles to bind back on where they are not wanted, the way a high pH detergent would. So for tie-dyers, batik artists and printers: this helps white and lighter colored areas from being stained in the final wash by the excess dye. We get calls all the time about "muddy tie-dyes" - the secret is in the Synthrapol! (Also in the procedure for rinsing out the excess first!)
Use 1/4 cup (2 oz) of Synthrapol per full washing machine load for cotton, Rayon, hemp, etc.
Use 1/8 cup (1 oz) for silks or if you have a front loading wash machine or high efficiency machine. Some folks say you can get away with less, but it depends on what you are doing, the hardness of your water, etc.
You can also find a more eco-friendly substitute for Synthrapol with our own Professional Textile Detergent.