Griffin Dyeworks & Fiber Arts

Understanding Mordants and Modifiers

MORDANT comes from the French, meaning "to bite." Mordants are mineral salts that bind dyes into fiber, assure light- and wash-fastness, prevent color bleeding, brightens or changes some dye colors. Over the centuries many interesting substances were used as mordants to ensure color fastness, including arsenic and other deadly chemicals. Early writers, most of whom were not dyers or chemists, often confused matters by often giving two different chemicals the same name.

CHEMICAL CARE: Mordants or modifiers must be kept tightly-lidded, out of direct sun, away from heat until use, and out of reach of children and pets. These chemicals often arrive in plastic bags for easy shipping and should be placed in a lidded glass or good plastic jar as soon as possible. Transfer all label information, including warnings, to the new container. Dispose of the plastic bag immediately.

IDENTIFYING MORDANTS: This is important if differently-mordanted fibers go in the same dyepot. It is especially important if mordanted fiber is stored for later use. Otherwise, you’ll never know which mordant/dye was used on which fiber. One method is tags cut from white Tyvek™ express mail envelopes. Don't use the printed sections of the envelope as that color will transfer to your dyed fiber. Cut out tags any size you wish and write on them with permanent felt-nib pens such as Sharpie™; use only the black pens as other colors are not as waterproof. Tie or safety-pin tags on fiber, but remove pins after dyeing as the metal may react to chemicals and stain the fiber.

A system of knots can also be used on yarns:

  • No mordant = no knot
  • Alum mordant = 1 knot
  • Copper mordant = 2 knots
  • Iron mordant = 3 knots
  • Tin mordant = 4 knots
Mordant Knots

PRE-MORDANT: This is simply mordanting before dyeing. Alum is the standard mordant used for this method but other mordants can also be used to good effect. Several differently-mordanted fibers can to go in one pot if they have been pre-mordanted, giving different color results without affecting each other.

DYEPOT MORDANT: Dyeing and mordanting at the same time is quick and easy, especially if using only alum. Dissolve mordant in a little water before adding to dyepot or color may be splotchy. Adding a pinch of alum or tin can often brighten a color; tin may entirely change the color results. Lift fiber out of dyepot before adding any more mordant.

POST- or AFTER-MORDANT: After dyeing the fiber, a mordant can give color surprises or perk up uninteresting colors. This is especially good for copper and iron mordanting. Alum tends to slightly remove some of the dye if carelessly used as a post-mordant.

TIMING for FIBERS: It does not harm fiber to stay in mordant longer than listed, but mordanting time should not be shortened. After mordanting is completed, fiber can be left in the pot while mordant liquid cools. At that point, all the chemicals fiber can accept have been firmly embedded in simmering, so rinsing will not remove mordant. Some mordants also color the fiber, which may or may not be desirable.

    1. YARNS: Simmer in mordant at least ¾ hour.
    2. COTTON: An 1800's recipe for preparing cotton suggests that you boil the fiber with alum and sumac, cool, boil the fiber in alum and sugar of lead, then again in sumac, and again in alum. All this before dyeing the fiber! A modern version is alum-tannin-alum mordanting (see below). Cotton should soak several hours to 1 full day in mordant to open the fibers, then simmer 3/4 hour in same mordant.
    3. SILK: Soak 24 hours in mordant, simmer 3/4 hour, same liquid. Silk needs an acid bath to accept dyes well, so a mild rinse of vinegar after mordanting will work well. Remove silk from heat after reaching boiling point in mordant, allow to cool and soak for a day.
    4. WOOL: Simmer 1 hour in mordant, cool in mordant water and rinse.
    5. COARSE FIBERS (Linen, ramie, homespun cotton or tightly-spun wool): Soak fiber several hours to 1 full day in mordant, then simmer in mordant at least 1 hour. Leave fiber in the pot and allow to cool, overnight if possible.

NO-HEAT MORDANT: Not as effective as simmering but best for delicate fibers that can’t take heat. Dissolve mordant in hot water, add fiber and steep overnight, rinse, dye. Don’t do this with thiox because the chemical will seriously affect fiber left to soak in it.

RINSING: Once a mordant is simmered into fiber, rinsing won't remove it. Alum and copper mordanted fiber doesn't need rinsing before going to the dyepot, but iron and tin mordanted fiber should be rinsed to prevent it from harming or stiffening fiber. Wash mordanted fiber in soap, rinse well, air-dry.

READY TO DYE: Fiber may be dyed as soon as it is removed from mordant pot or if there are time constraints, the fiber may be dried and stored for later use. There seems to be little difference in freshly-mordanted or stored mordanted fiber. Store in labeled cloth or paper bags until needed, not in plastic bags.

MODIFIERS: These are chemicals that assist dyeing; they can help fix color into fiber but are not strong enough in themselves to be considered mordants. Modifiers can change dyebath from acid to alkali (and vice versa) to enhance or affect colors. They should be added according to individual dye recipes.

NEUTRALIZING CHEMICALS: Most mordants and modifiers are absorbed into the fibers with very little left in the pot. When dyeing is done, dilute any leftover chemicals with lots of water. When chemical is thoroughly diluted, it is safe to neutralize the chemicals with a very mild version of the opposite chemical. For example, if the chemical used is acid, then add baking soda to the dilute acid. If the chemical used is alkaline, then add vinegar to the dilute alkali.

SAFE DISPOSAL: When ready to dispose of any well-diluted and neutralized mordant or modifier chemicals, follow directions under each listing below.

AMOUNTS LISTED are for mordanting 1 lb fiber in 3-4 gallons of water.

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

DISCLAIMER: Griffin Dyeworks & Fiber Arts gives the following information in good faith, based on technical data judged to be reliable, and makes no legally binding assurance or warranty—express or implied—as to fitness of any product for a particular purpose and shall under no circumstances be liable for incidental or consequential damages, since the conditions of use and the many factors that may affect processing and application are beyond our control. It is the user's responsibility to exercise independent judgment in determining any product's appropriateness and/or suitability for a specific purpose, to develop proper methods of handling as well as suitable disposal of product. Further, nothing contained herein shall be construed as a recommendation to use any product in conflict with existing safety warnings.

© 2012 Griffin Dyeworks & Fiber Arts