Country or region: UK
Message: Hey, I dyed some silk chiffon (100% silk) a dark plum/burgundy/maroon colour with an acid dye and am hoping to tie-dye it in a lighter, more pink plum shade, again with another acid dye. My worry is that double dying it may cause the fabric to waste away (which is what happened when I tried to bleach it lighter after it was dyed) and that using elastic rubber bands may damage the fabric. Another worry is that the colours may go bad when double dyed. Any chance you could help out with some advice?
Dyeing a piece of silk twice with the same type of acid dye won't hurt it, but you can't dye a dark plum to a lighter color, because dye can only make things darker. Dye can never be used to lighten any color of fabric.
Whenever you add dye to a fabric, you are adding color. Adding more color makes it darker. Dye is transparent, so the original color always shows through. Adding one color on top of another color gives essentially the same results as mixing those two colors together. To obtain a lighter color with acid dyes, you must use less dye to start with, so the white of the fabric shows through. You can try to cover one dye with another dye only if the second dye is darker in color.
The reason why your bleaching caused your fabric to "waste away" is because bleach destroys silk. Never use chlorine-based bleach on any animal-based fiber, such as silk or wool, nor on any synthetic fiber, such as nylon or spandex. The way that chorine-based bleach works to remove color is by breaking apart the dye molecules; the hypochlorite in chlorine-based bleach will break up most chemicals that it encounters, including the protein molecules that silk is made of. It will do the same thing to your skin if you allow enough exposure to it. Bleach is much more toxic and dangerous than dye is, both to fabric and to people.
There is a completely different class of chemicals that can be used to remove dye, but the color you get as the result of it may not be the sort of color you are looking for. You can use a reducing-type dye discharge chemical safely on silk, if you are careful to follow the instructions. Some brands include Formosul (available in the UK from George Weil) and Rit Color Remover; see my page, "What chemicals can be used to remove dye?". If you use too much of the discharge agent, or don't follow the instructions, you may damage your silk, but the discharge agent is far gentler than chlorine-based bleach, and can be used safely if you are careful. If the color you obtain is light enough, you can dye over it with acid dye to another color; dyeing your entire dark plum piece with a light plum dye should work well, as the light plum dye will darken the pre-existing dark plum only a little. Some dyes will discharge with a reducing-type dye discharge chemical to nearly white, though others will turn a ghostly brown or refuse to lose color at all. Depending on which acid dye you used, you may be able to learn from the manufacturers whether the specific dye color molecules you have chosen are capable of discharging, and, if so, what color they will discharge to; for example, the dischargeabilities of most of the Jacquard Acid Dyes are listed on the Jacquard Products website. [PDF]
If you happen to have chosen an acid dye that will discharge well, you can apply a discharge agent such as Jacquard Discharge Paste or Deco Reco Decolourant to just those areas you wish to lighten in color, or you can tie the silk tightly, as for any tie-dyeing, and then heat it in a discharge bath with Formosul, Rit Color Remover or another discharge chemical, carefully following a good set of instructions. If you can't use elastic rubber bands without damaging a delicate fabric, try tying with string, instead. Try different types of string to see which you prefer; I like to use a wax-coated polyester string called artificial sinew.
There is one other possibility for placing a light pink plum color on top of a dark plum/burgundy color. Instead of using dye for your second color, you can use fabric paint. Some paints are harsh and stiff on the fabric, but some brands of fabric paints are thin enough to be very appealing on silk. Look at your local crafts store, or on the website for a dye supply company (such as George Weil, in the UK), for any fabric paint specifically marketed for use in painting silk. It's important to note that most fabric paints are transparent, so they can cover a darker color with a lighter one only if they are specifically labeled "opaque"; however, if you're interested in a metallic or pearlescent effect, diluted Jacquard Lumiere can work beautifully on silk. Jacquard Dye-Na-Flow is available in a white color which will not work well in covering a dark-colored fabric, but may suffice for lightening the color a little. Test it first on a scrap piece of colored fabric.