I've never washed DMC threads before I've stitched with them, and I have frequently washed finsished pieces, and not had problems. I've only ever handwashed cross stitch in luke warm water, with a bit of fairy liquid in it.
But I have shoved older tablecloths embroidered with DMC into the washer on 30 degrees and again had no problems. I use a color catcher, that I buy at the supermarket, just in case, but it's always come out clean, so I probably haven't needed it.
I do prewash my fabrics though. To get out those stubborn fold creases, and to check for any potential shrinkage, before I put my embroidery on there. I've seen the results when the ground fabric has shrunk, and the embroidery floss hasn't. It isn't pretty.
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grote stukken was ik altijd omdat ik er te lang mee bezig ben geweest. De laatste stukken bewaar ik tegenwoordig in plastic als ik er niet mee bezig ben, zo blijven ze mooi
When I first started stitching some 20 years ago, I used to "set" my dmc floss before using. It was a combination of vinegar and water and then rinse in water. Well, I took a break from stitching for a few years and when I came back I never "set" the dmc floss again. And I haven't had any troubles with color bleeding.