Folk School

Scouring and Mordanting Wool

Preparing a pound of wool for the dye pot: weigh it dry, scour out the grease and sizing in lukewarm suds without felting it, then mordant it in alum and cream of tartar for an hour and let it cool overnight. How cotton differs, with its three-bath alum, tannin, alum method.

  • 5 min
  • 6 steps
  • 3 questions
  • Lesson 106 of 204

In this lesson

  1. Weigh it dry
  2. Scour
  3. Mordant with alum
  4. Cotton is harder
  5. Try it

Most dye failures start before the dye pot. Greasy wool takes color unevenly, mordanted wool that went in dry comes out streaked, and wool that was shocked with hot and cold water comes out felted. The fix is a slow, careful preparation.

Four numbered panels. One, weigh dry: a skein on a scale reading 1 lb; every amount depends on the dry weight; recipes here are for 1 pound. Two, scour: a skein in a pot; 5 gallons at 95 degrees, 3/4 ounce neutral soap, 30 minutes; again with 1/4 the soap; rinse 3 to 4 times. Three, mordant: 4 ounces alum plus 1 ounce cream of tartar in 4 to 4 and a half gallons; enter wet, heat slowly, 1 hour, cool overnight. Four, rinse, then dye: squeeze out, store wet or dry, rinse just before the dye bath. Below left, don't felt it: heat, sudden temperature changes, and rough stirring shrink and felt wool; keep suds and rinses the same temperature, move the wool gently, squeeze, never wring or twist. Below right, cotton is harder: it takes metal mordants poorly; alum plus washing soda for 1 hour, or alum, then a tannin bath of oak galls, sumac, or tannic acid, then alum again, three baths over three days.
Weigh, scour, mordant, rinse. Credit: StudyCorner diagram after USDA (1935) and Earth Guild · CC BY 4.0 · Source

Weigh it dry

The weight of the yarn decides how much soap to wash it with and how much mordant and dye to use, so the first step is to weigh it while it’s dry 1. Every recipe in this course is for 1 pound of dry wool. For half a pound, halve everything 2.

Wind the yarn into skeins and tie each one loosely in several places, a tight knot with a loose loop. If the ties are snug, the dye can’t reach under them, and you’ll get tie-dyed yarn 2.

Quick check

Why weigh the wool before anything else?

Scour

Dye can’t penetrate grease, starch, or sizing, so the yarn has to be washed clean first 1. The USDA’s method for wool 1:

  1. Make suds with about 3/4 ounce of neutral soap in 5 gallons of soft water at about 95°F, lukewarm. Wash the wool for 30 minutes and squeeze out the suds.
  2. Wash it again for 30 minutes in lukewarm suds with a quarter as much soap.
  3. Rinse 3 or 4 times, 10 minutes each, in lukewarm water.

The rules for keeping wool from felting: move it from bath to bath without delay, keep the suds and rinses the same temperature and never more than lukewarm, and squeeze the water out evenly. Never wring or twist it. Sudden changes in temperature make wool shrink and turn harsh 1. Heat plus agitation is exactly how felt is made, so stir slowly and gently 2. Store-bought yarn is usually clean already, but it still needs a long soak so it wets evenly 2.

Quick check

What makes wool felt and shrink while you’re scouring or mordanting it?

Mordant with alum

The USDA’s alum mordant for 1 pound of wool 1:

  • 4 ounces potash alum
  • 1 ounce cream of tartar

Dissolve both in 4 to 4½ gallons of cold soft water. Put in the wool wet, squeezed out but never dry, because dry fiber in a mordant or dye pot streaks 2. Heat gradually, turning the wool, and keep it hot for 1 hour, adding water as it evaporates. Let it cool overnight in the bath 1. The 1935 recipe says to boil gently; Earth Guild’s instructions say to hold it at a simmer and not boil, since heat and agitation felt wool 2. A simmer is the safer choice.

In the morning, squeeze out the wool. Rinse it well just before it goes into the dye bath 1. Alum-mordanted wool keeps, wet or dry; if you store it dry, soak it well before dyeing 2.

How much alum? Earth Guild suggests 3 ounces with 1 of cream of tartar as a start, 4 for heavy wool, and warns that too much alum makes wool sticky. Cream of tartar helps the mordant take evenly and brightens the color slightly 2.

Natural Dye Basics: How to Premordant Wool Yarn with Alum Pre-mordanting wool yarn with alum and cream of tartar. Credit: Last Minute Laura · YouTube standard license · 10:46 · Source

Playback is optional. If the player is unavailable, open the video at its source.

Quick check

How much alum does the USDA call for per pound of wool?

Cotton is harder

Cotton and other plant fibers don’t take metal mordants the way wool does, but they combine well with tannin 1. The USDA gives two methods for a pound of cotton 1:

  • Alum and soda: 4 ounces alum and 1 ounce washing soda, boiled for an hour and left overnight.
  • Alum, tannin, alum: half of 8 ounces of alum and 2 ounces of washing soda, overnight; then a bath of oak galls, tannic acid, or sumac-leaf extract at 140–160°F for an hour, overnight; then the rest of the alum and soda, overnight again.

Cotton is scoured hotter than wool, at 140°F, because it won’t felt 1.

Try it

Divide your pound of yarn into four skeins of 4 ounces each, and scour and mordant all four together, using the full pound’s quantities. Leave the skeins wet in a bucket, or dry them for later; you’ll use them in the dye lessons ahead.

Lesson complete

Nice work.

1day streak
0/1today's goal
–correct

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The Dye Bath and Testing for Fastness

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Sources for this lesson
  1. 1
    Margaret S. Furry, Bess M. Viemont. Home Dyeing with Natural Dyes (Miscellaneous Publication No. 230). U.S. Department of Agriculture, Bureau of Home Economics. 1935. verifiedTests of about 65 natural dye materials on cotton and wool; only colors fast to light and washing were given recipes. Wool dyes most easily; cotton only by complicated processes. Home light test: dyed cloth between two cards with matching 2-inch windows, outdoors tilted toward the sun a few days. Home wash test: 2 by 4 inch dyed piece sewn to undyed cloth. Equipment: scales, enamel or copper kettles (iron darkens, tin makes colors harsh), measures, cheesecloth, smooth sticks, thermometer, rubber gloves, line in the shade, soft water. Weigh dry first. Wool scour: 3/4 oz neutral soap per pound in 5 gal at 95 F, 30 min, again with 1/4 the soap, rinse 3 or 4 times at the same temperature; never wring; sudden temperature changes shrink wool. Mordants: alum, chrome (potassium dichromate), copperas, tannin. Wool alum mordant: 4 oz potash alum and 1 oz cream of tartar per pound in 4 to 4 1/2 gal, heat gradually, boil gently 1 hour, cool overnight. Cotton: alum with washing soda, or alum-tannin-alum. Dye baths: at least 4 to 4 1/2 gal per pound or streaks; wool in lukewarm, heat gradually, keep moving; rinse until clear (crocking from poor rinsing); dry in shade; dye all of a color at once because natural colors can't be matched. Not fast: annatto, barberry root, beets, crab-apple peel, blackberry, blueberry, cranberry, pokeweed, purple iris, mosses, peach leaves, red roses, sumac leaves, turmeric, willow leaves. Bark colors combined with tannin often darken in light. Butternut hulls (alum) fast brown, iron darkens to black. Cochineal from an insect of Mexico and Central America; alum, 1 oz per pound, American beauty red; not for cotton. Goldenrod flowers picked coming into bloom: with alum, greenish yellow not fast to light; with indigo dark greens; with madder terra cotta. Indigo needs no mordant; vat dye reduced and dissolved in alkali; greenish yellow in the vat, blue in air; fermentation blue-pot (8 oz indigo, 4 oz bran, 4 oz madder, 1 1/2 lb washing soda, 4 gal, 85 F, 5 to 10 days) and hydrosulphite vat. Madder: Egyptians, Moors, Netherlands; replaced by synthetic alizarin; 8 oz per pound with alum, lacquer red, very fast; dark red at 140-160 F without boiling. Onion skins 10 oz dry, alum: burnt orange, fair. Black walnut hulls on unmordanted wool: dark brown, good; long boiling makes wool harsh. Lichens used by peasant dyers of Sweden, Scotland, and Ireland. Top-dyeing: clear colors make clear colors; goldenrod plus indigo green; indigo plus walnut black or gray; goldenrod plus madder terra cotta.
  2. 2
    The Mordant Riff. Earth Guild (Asheville, North Carolina). 1998. verifiedSubstantive dyes (lichens, walnut hulls) need no mordant; adjective dyes do: the mordant enters deeply into the fiber and the dye combines with it. Wool is easiest. Non-reactive pot, unchipped enamel or stainless; brass, copper, or iron pots mordant on their own. Soak wool several hours; never put dry fiber in a mordant or dye pot. Simmer an hour, do not boil; heat and agitation cause felting; cool overnight. Mordanted wool can be stored wet or dry. Never use the same pots for cooking and dyeing; don't breathe fumes. Alum with cream of tartar: 3 oz alum and 1 oz cream of tartar per pound, 4 for heavy wool; too much makes wool sticky. Iron saddens; tin blooms but is caustic and makes wool brittle; blue vitriol is poisonous. Test colorfastness; fading happens with berries and some flowers.

Further reading

  • Natural Dyeing. Earth Guild (Asheville, North Carolina). 2000. verifiedWash wool at least twice in warm soapy water; tie skeins loosely in several places. Three methods: mordant first, mordant and dye together, or dye then mordant; recommends pre-mordanting with alum. Madder 8 oz per pound of wool; madder should not be heated beyond a simmer, because boiling releases brown dyes. About four gallons of water per pound of fiber. Enter wet wool into a tepid bath, heat slowly, avoid abrupt temperature changes, stir gently; colors are darker wet than dry.

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