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Mordants and Metal Dyes

History of Metals in dyeing:

Metals are among the earliest of dyes for textiles. Most commonly, early people from all over the world discovered that certain soils would impart color to cloth if the cloth were buried in it for some duration. Extant examples of such a technique can be found in textiles of the Swiss Lake Dwellers, approx. 3000 BC and modern use of the practice can be found in Africa, where the natives treat the cloth with a pattern of tannins and then bury it in iron-rich soil, producing a black and tan design.

References to metals and mordants in period dye recipes are numerous. Unfortunately many terms used to refer to dye substances are ambiguous, and some terms meant different substances in different times or places. As a result, analysis of exactly what chemical mordants were used relies sometimes on inference. Recipes vary widely in their application of mordants; some instruct pre-mordanting, some call for the mordant(s) to be added directly to the dyebath, some would have you dip the dyed fibers into a mordant afterwards, and some combine two or more of these methods.

NOTE: Please read the Dyeing Safety section on the Natural Dyeing Basics page before using mordants or metal dyes!

Iron - very common, usually called "copperas". "Saddens" or darkens colors. Used in very dark colors; black, olive, silver, "tristemon". Iron tends to break down fibers and leave them feeling harsh and brittle, so thorough rinsing is advised. Iron is somewhat poisonous in large quantities.

  • ferrous sulfate, hydrated, FeSO4 * 7H2O. Called copperas, Green Copperas, green vitriol. ferrous acetate, Fe(C2H3O2)2, ferrous chloride, FeCl2, and ferrous nitrate, FeNO3 can sometimes be used interchangeably with ferrous sulfate.
  • ferric sulfate, Fe(SO4)3. Called nitrate of iron.
  • ferrous oxide - Called nankin. (Rust is actually a mixture of Iron oxides)

Chrome - first available 1797, brightens colors, sometimes to "unnatural" levels. Lead and chrome can be combined to make a bright yellow. Chrome is highly toxic.

  • Potassium dichromate, K2Cr2O7

Tin -First documented use was by Dutch chemist Drebbel in 1630 with cochineal. Brightens colors, sometimes to "unnatural" levels. Tin is more poisonous than iron or copper but not as toxic as chrome.

  • stannic chloride, SnCl4
  • stannous chloride, SnCl2

Copper - common, often called verdigris or copper vitriol. Don't confuse with plain "copperas" which is usually iron. Tints colors towards coppery orange (reds and browns) or verdigris green (yellows and blues). Used in sulfur yellow, blue, greens, oranges. Copper can be poisonous in large quantities.

  • copper acetate, CuO * 2 Cu (C2H3O2)2. Called verdigris, verditer.
  • copper sulfate, CuSO4 * 5H2O. Called copper, copper vitriol, blue copperas, blue vitriol, Roman vitriol, bluestone

Alum - very common. Brightens colors. Used in almost every color range. Too much on wool can make fibers "sticky". Least poisonous of the metal mordants, can be used with children as long as safety precautions are followed.

  • aluminum acetate, AlC2H3O2, called alum, acetic acid alum
    came into use 1750-1790 (Liles), refine bauxite using acetic acid
  • aluminum potassium sulfate, AlK(SO4)212H2O. Called alum, potassium alum,. Made by refining bauxite using potassium
  • aluminum ammonium sulfate, Al2(SO4)3(NH4)2SO4 * 24H2O. Called garden alum, pickling alum, aluminum sulfate. 2oz. Alum sulfate = 3oz. Potassium alum, refine bauxite using sulfuric acid. Very common, found in salt mines, certain lichens. Most likely "alum" in period manuscripts.

Other substances that act as mordants or "assistants":

Tannic Acid - C76H82O46. Very important in early dyeing. Produces the color tan. Most commonly gotten from "gallnuts" (walnut husks or oak galls depending on translation) in period but could also be found in other plants; sawdust (oak, cutch, walnut, etc.), leaves from various trees, wood ash, and red wine are other cited sources. Modernly, sumac trees and tea are common substitutes.

Oxalic Acid - HO2CCO2H. Found in rhubarb. I haven't found a period recipe calling for it yet.

Acetic Acid - CH3COOH. Common. Found in vinegar (5%) and wine.

Cream of Tartar - Potassium hydrogen tartrate or Potassium bitartrate, KHC4H4O6. Acid. Called argil, argal, argol., tartar. Tartaric acid CO2HCHOHCHOHCO2H is found in grape skins. Cream of Tartar is found as a deposit left in wine casks.

Ammonia/Urine - Ammonium hydroxide, NH4 OH. Called chamber-lye, sig. Very common. Alkaline.

Lye/Wood Ash - Potassium Carbonate, K2CO3. Called potash, pearlash. Very Common. Alkaline.

Washing Soda - Sodium Carbonate. Called soda ash, salt of soda. Alkaline.

Potassium Nitrate, KNO3. Called Saltpetre. Common.


All recipes are for 1 pound of fiber; weigh your fiber and then multiply or divide the amounts in the recipe by that number to get the actual amount you should use. Always make sure you have ample water so the fibers can move freely. For best results, remember to move fibers about to promote even mordanting. Adding an acid to animal-based fiber in a mordant bath promotes optimal usage of the mordant, while adding a base (alkaline) to a plant-based fiber does the same.

NOTE: Please read the Natural Dyeing Basics page first, paying special attention to the Dyeing Safety section!

Copper Seafoam Green:

Dissolve ounce of Copper Sulfate completely before entering the fiber. Boil until the color no longer seems to be getting darker.

Dark Seafoam Green:

Add a small bit of iron to the above recipe, or dip fibers in iron bath briefly after the copper bath.

Iron-tannin Greys to Black on Linen, Cotton, or silk:

Prepare 2 baths, one with about 1-2 ounces of pure tannic acid (more if using a solid plant source) and one with 3 ounces of copperas or another ferric salt (less for cotton, more for silk). Place the fibers in the tannic acid bath for at least three hours. Rinse and move to iron bath for 30 minutes. Rinse and move back to tannic acid bath for another hour. Rinse and keep alternating between the tannic acid and iron until the desired shade is reached.

Iron-copper-tannin Greys and blacks on wool:

Dissolve 2 ounces copperas, 1 teaspoon of copper sulfate, and ounce of tannins (2 ounces of osage orange, cutch, or fustic sawdust) in a pot. Enter the fibers and boil until desired shade is reached.

For a darker black, separate the copperas and copper sulfate into one bath and the tannins into another bath. Alternate baths in a similar manner to with the previous recipe.

Iron Buffs (best on cotton and linens):

Dissolve 2 teaspoons of copperas (low-grade) in a pot. Work the fibers for 15 to 30 minutes. Rinse and immerse in a hot-but-not-boiling bath of 3 teaspoons washing soda. The iron will precipitate as a greenish-gray color. Lift the fibers and allow to air. The color should change to orange or rust. Repeat entire process for a darker shade.

Alternately, bury your fiber in iron-rich mud for a week or more.

All content copyright the author, Jennifer Munson munson.jennifer@gmail.com The author makes no guarantees for instructions and recipes on this site; neither does she accept responsibility for their outcomes. Verbatim copies may be made for educational purposes only provided they contain original copyright marking.

This page created August 4, 2001

Last updated May 14, 2004