We get a lot of questions about the workings of and differences between color remover, discharge paste, and bleach. In textile dyeing it's often usefull to know not only the steps to achieve a result but also what's happening behind the scenes, so to speak.
To that end our intrepid chemist, Michael Katz, has put together a detailed explanation of the inner workings of these three chemicals. See it at: About Color Remover, Discharge Paste, and Bleach.
Thank you for bringing this to our attention - we'll see about repairing this link in the next couple of days. In the time being you can find this article at our website in the FAQ's. anet
I use thiox, soda ash and heat to do my discharging and have come across items that will not discharge or as you stated in your article return to their original color after the discharge bath. You mentioned "The answer is that vat dyes needs to be reduced to go into solution." I'm not clear, is there another reducing agent that can be used to get those dyed fabrics to hold the discharge? Or am I reading this wrong? Thanks, Jo
Hi Jo, This questions really gets to the heart of vat dye chemistry. Vat dyes require reducing agents to become water-soluble, and reducing agents and discharge chemicals are one and the same thing. A vat dye will not dissolve in water unless it is in its reduced (oxygen-free) form (often called the leuko state). The fiber is immersed repeatedly in this oxygen-free dyebath, then exposed to the air, whereupon the water-soluble, reduced form develops its color as oxygen turns it to the water-insoluble form. Indigo is an example of this dye class; it changes from yellow, in the dyebath, to green and then blue as the air hits it. When you try to discharge a vat dye, you are reducing it and putting it back into its leuko state. It will lose its color only until it is exposed to oxygen (air) again and re-oxidizes. This is why the color can return after discharging. The only way to successfully discharge a vat dye is to rinse out the reduced dye while it is in its water-soluable, leuko state. This can be tricky, but it is not impossible. Once you see that the color has discharged (or in this case, reduced to the leuko state), you must rinse it out quickly and thoroughly. (Use Synthrapol for best results). The more of the reduced dye you can rinse out, the more it will "hold" the discharge... I hope this is helpful! Asher
Thank you Asher...very helpful to know what's happening. I've discovered this a little on my own when I've come across garments that won't discharge down to a light color. I have been rinsing immediately after the discharge bath, getting some varying results. Though I've never tried rinsing with synthrapol at that point. I will give it a try. Thanks again, Jo
