The Dye Bath and Testing for Fastness

Each dye in the next module has its own recipe, but they all share one procedure. The USDA spelled it out once, and it’s worth learning before your first pot.

Rules for every dye bath

The bulletin’s general rules, all based on 1 pound of wool weighed dry before mordanting ¹:

• Prepare the dye. Weigh or measure the plant material, extract it as the recipe says, usually by soaking and boiling, and strain it into the dye bath, so twigs and bits don’t tangle in the yarn ².
• Use plenty of water, at least 4 to 4½ gallons of soft water per pound. Crowded yarn comes out streaked or spotted ¹.
• Wool goes in lukewarm. Rinse the mordanted yarn, squeeze it lightly, and put it in a bath that’s just lukewarm; cotton can go in warmer. Then heat gradually and simmer or boil as directed ¹. Avoid sudden temperature changes throughout, and stir gently ².
• Keep it moving. Keep the yarn opened out and turning so all of it heats evenly ¹.
• Keep the level up. As the bath boils down, lift the yarn out and add boiling water, so the amount of liquid stays the same ¹.
• Rinse until clear. Rinse first in water the temperature of the dye bath, then cooler, and keep going until the rinse water is clear. Color that rubs off later, called crocking, usually means too little rinsing ¹.
• Dry gently. Squeeze out the water; don’t twist or wring, which leaves streaks. Roll the yarn in a towel, shake it out, and hang it in the shade ¹.

Remember that wet wool looks darker than it will dry ². For a lighter or darker shade, use less or more dye material ¹.

Dye it all at once

Plants vary from place to place, season to season, and year to year, so a natural dye color is almost impossible to match a second time. Dye all the yarn a project needs at once, instead of trying to match it later ¹. Keep notes on every batch in case you want to come close ³.

Test the color

No dye is fast under every condition. A color may stand up to light and not to washing, or hold on wool and not on cotton ¹. How fast it needs to be depends on the use: a bark brown that darkens in the light might be fine in a hooked rug and a problem in curtains ¹. The USDA rated its colors with laboratory equipment, but described two tests you can do at home ¹.

Light test. Cut matching 2-inch square windows in two pieces of heavy cardboard. Fasten a piece of the dyed yarn or cloth to one, cover it with the other so the windows line up, and set it outdoors in direct sun, tilted toward the sun. After a few days, compare the exposed square with the covered part. The USDA rated a color good if there was no noticeable change, fair if the change was noticeable but not objectionable, and poor if it was objectionable ¹.

Wash test. Sew a 2-by-4-inch piece of the dyed material to a piece of undyed material the same size. Wash it in warm soapy water, rinse it several times, dry it, and compare it with an unwashed piece. This shows both fading and bleeding, color running onto the white ¹.

Colors that don’t last

Some plants famous for staining fingers don’t make lasting dyes. The USDA left these out because the colors weren’t fast on wool or cotton: annatto seeds, Japanese barberry root, beets, crab-apple peelings, blackberries, blueberries, cranberries, pokeweed berries, purple iris, mosses, peach leaves, red roses, sumac leaves, turmeric, and willow leaves ¹. Earth Guild says the same: complete fading is unusual with mordanted wool, but it happens with berries and sometimes flowers ³.

Try it

When you dye your first skein in the next lessons, cut two short lengths of it. Put one in a cardboard light-test frame in a south window or outdoors, and wash the other sewn to a scrap of white cotton. Label both and check them after a week.