Description: Acid mordant, translucent crystalline water-soluble element, 3.2 pH; used earlier than 2000 BCE, found near sulfur springs, in salt mines, and in 250+ plants (alum-root (Heuchera) contains tannin not alum)
Other Names: Aluminum potassium sulfate, alem, alum flour, alum meal, alum root, arga, burnt alum, cube alum, dodecahydrate of alum, exsiccated alum, kalinite, oxide of aluminum, potash alum, potassium alum, rock alum, Roman rock, [Old] alunite, allom, argil, [Lat] alumen, alumina, alumini, allume, [ME] alume, [OE] alefne, aelif-nae, Ger] alaunen, alaun, [Fr] aluner, [Sp] alumbre, [Aztec] thal-xocotl, [Navajo] rock salt.
Dye Use: Attracts moisture from the air, used as a dye fixative, color brightener. A pinch of alum makes color flow, too much alum makes fiber harsh, sticky. Hang wet alumed wool in the dark for 3 days to make it accept dyes better. Rinse fiber thoroughly so unfixed alum won't affect dye results.
Best On: Wool, silk
Dye Recipe: General measurements: 2 1/2 tbsp to 1 lb fiber, plus 3 tbsp cream of tartar. Early dye books suggest 4+ tbsp alum to 1 lb fiber but less alum means softer fiber. Refresh alum pot with 5% more alum, 2.5% more cream of tartar. See Ammonium sulfate for cotton and linen mordanting.
Wool Mordant: Dissolve 2 tsp alum, 1/3 c bran, 1 tsp Glauber's salt in 1 gal water, add soaked fiber, simmer 30-60 min at 175°F. Add 3 tbsp cream of tartar in last 15 min of simmering. Fiber may be left in mordant overnight or longer. Rinse in warm water with 2 tbsp bran, which helps remove unabsorbed alum.
Silk Mordant: Dissolve 2 tsp alum, 1/2 tsp soda ash, 2 Tbsp bran in 1 gal water, add wet silk. Simmer 20 min and soak 10 min for light silk; simmer 1 hour and soak 1 hour for heavy-weave silk in hot mordant. Add 2 tbsp vinegar to last rinse to give silk a crisp hand (feel).
Safety: Not considered very toxic; used in foods; slight skin and eye irritant, don't inhale it.
Disposal: Pour down sink or on plants.
Alternatives: Salt + baking soda, old aluminum pot, pickling alum (aluminum ammonium sulfate)
Source: Griffin Dyeworks, Mexican food section of grocery store
CODES: c = cup; gal = gallon; lb = pound (weight); tbsp = Tablespoon; tsp = teaspoon / [AF] Anglo-French; [Ar] Arabic; [AS] Anglo-Saxon; [Dan] Danish; [Du] Dutch; [Fr] French; [Ger] German; [Gk] Greek; [It] Italian; [L] Classical Latin; [LL] Late Latin; [ME] Middle English; [ML] Modern Latin; [OE] Old English; [OF] Old French; [ON] Old Norse; [OS] Old Saxon; [Port] Portuguese; [Sp] Spanish; [Sw] Swedish / CE = Common Era; BCE = Before Common Era