I recently dyed some pieces of silk and gauze. Once the silk takes one color of dye can it be overdyed a darker color? The colors I got were not what I expected. In one a green color took over the piece. I have tried over dying the green with cobalt and it’s not doing anything. I would love any advice you have to offer.
Thin silk is limited, as you’ve seen, in how many dye molecules it can take up. While thicker fabrics such as a heavy raw silk, or the cotton jersey of t-shirts, can add more color through six or more rounds of dyeing, a very thin sheer fabric, such as chiffon or gauze, may do so through only one or two rounds of dyeing, refusing to change color further when you dye it again.
Physical manipulation of the fabric, as by rough washing, can free up more dye sites in a fabric, but that’s not a good idea with fine silks.
Removing the dye color with a dye discharge chemical, such as thiox, will probably not help, because the dye molecules will still be bound to the fabric even after they have been decolorized by the reducing agent. The hypochlorite in chlorine bleach might chew up enough of the surface of the fabric to reveal more dye sites, if you’re dyeing cotton gauze, but you should never use chlorine bleach on silk, since it is very destructive to protein fibers.
You might be able to add another layer of color if you use an entirely different class of dye which attaches to the molecules of the fabric in a different way. For example, if you have been dyeing your silk with Procion dyes plus soda ash, you might find that dyeing them with acid dye plus an acid, such as vinegar, will allow one more round of color—or if you’ve been using acid dyes, which includes Procion dyes that have been set with an acid rather than soda ash, then you might try dyeing with Procion or another fiber reactive dye, and setting it with soda ash. Definitely a matter of trial and error, no guarantees that it will work, but it is worth experimenting.
Also see my earlier post, “Will a fabric reach a saturation point after which it cannot take any more dye, or any more dye of a given colour?“.
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