Synthrapol works best with HOT water, yes, HOT water!
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 consistant 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. 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 washing machine load for cotton, Rayon, hemp, etc. and 1/8 cup (1 oz) for silks or front loading wash machines. Some folks say you can get away with less, but it depends on what you are doing, the hardness of your water, etc.
Our special new Low Foam Synthrapol is better for those front loading washing machines. Use 1/8 cup (1 oz) per load.