Although every effort is made to make threads colorfast, no manufacturer guarantees that the color won't "run." As dyeing by-products and waste can have a negative impact on the environment, Congress enacted laws which, down the line, caused manufacturers to change their dye processes. To stitchers, this means threads which once were essentially colorfast are not anymore.
Therefore, is it necessary to "set" the dye on floss before using it? Is just rinsing it of extra dye a feasible alternative?
If you are making a piece that will be washed because of its use, you may want to pre-rinse (and let dry) any dark colors you are using (666, 550, 500, 310, etc.). Two benefits:
There are several "old stitchers' tales" floating around, such as "soak in salt water" and "soak in vinegar water" to set the dye.
I believe this is risky business. Because you don't know what mordant was used in the dye process, you run the risk of damaging your floss.
I would rinse if I thought the floss would leave tracks. Otherwise, I'd do nothing.
After you stitch you piece, you will want to wash it to remove accumulated soil, excess dye from non-dark colors, and so on. The above-referenced file discusses this.
copyright 1999, Martha Beth Lewis
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