Daily Archives: January 20, 2015

Can you share the best method for removing color from an old wool rug?

Name: Kate

Country or region: Pennsylvania

Message: Hello,
Can you share the best method for removing color from an old wool rug? Thiox seems to only remove the color on a few random spots, not all over.

I’m afraid that there is no product that will work better than the one you’ve tried.

There are two problems with trying to remove the color from an old wool rug. One is that not all dyes can be removed at all. The other is that you can only remove the dye that you can reach. If the dye is covered with invisible dirt, spilled oil, spilled wax, stain-resistant spray, or just about anything else, the dye will be protected from any chemical you try to treat it with. You have to get the rug very, very clean in order to access the dye, but some stains are impractical or impossible to remove.

Even if you get all dirt and other coatings off of the rug, though, there’s no great likelihood of removing all of the dye. Whether you can remove any of the dye depends on what specific dye it is. You can never tell what dye was used on a commercial product, though; even if you know with one item, an identical item from the exact same suppliers may be dyed with a non-removable dye the next time. Some dyes can be removed easily with a reductive discharge chemical such as thiox; some can be removed by an oxidative discharge such as bleach; some can be removed with either; but some dyes cannot be removed with any chemical you try, no matter what you do. In some cases, you can destroy your fabric, leaving it in rags, and still have color in it.

Wool is easily damaged by high pH. Like your hair, wool requires mildly acid conditions, to protect it. A high pH may lead to obvious damage or to felting. Most color removers are used at a high pH (alkaline or basic), instead of an acid pH. Thiox, which is a brand name for thiourea dioxide, is an excellent color remover, but you do have to be careful not to damage wool when using it, due to the high pH of recipes that call for thiox. PRO Chemical & Dye provides instructions for using thiox to remove dye from cotton, silk, or wool, which also call for soda ash, resulting in a high pH; see their page, “Thiox: Thiourea Dioxide”. Note that recipes for thiox require quite a bit of heat, heating the discharge bath to at least 175 degrees F (79 degrees C); if you used thiox in cooler water, you might find that you have better results with the right temperature. Be sure to neutralize the soda ash in the wool by rinsing with a mixture of vinegar in water afterwards.

Other reductive-type color removers, such as the sodium hydrosulfite in Rit Color Remover, or sodium hydroxymethanesulfinate, which is sold under the name Formosul, will not produce significantly different results than thiox. Formosul is generally considered the best choice for removing color from wool, because it can be used at a nice gentle acid pH, but it will not do a better job than the thiox you tried already, assuming that you used a good recipe for the thiox, and enough heat. PRO Chemical & Dye’s recipe for using Formosul shows the use of citric acid instead of the soda ash used with other discharge chemicals.

As you probably already know, oxidative bleaches, such as the hypochlorite in chlorine bleach, will damage wool much worse than the reductive discharges such as thiox or formosul. I strongly recommend against even trying it. Chlorine bleach is good only for natural cellulose fibers, such as cotton, linen, or hemp.

For more info on dye removal, please see my page, “What chemicals can be used to remove dye?”.

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-Paula