Contrary to popular opinion, natural dyes are often neither safer nor more ecologically sound than synthetic dyes. They are less permanent, more difficult to apply, wash out more easily, and often involve the use of highly toxic mordants. Some natural dyes, such as the hematein derived from logwood, are themselves significantly poisonous. Of course, the color possibilities are far more limited; the color of any natural dye may be easily copied by mixing synthetic dyes, but many other colors are not easily obtained with natural dyes. However, some mordants are not very toxic, and the idea of natural dyestuffs is aesthetically pleasing.
Wool is generally the best fiber to color with natural dyes. It will attach to a wider variety of dye chemicals than cellulose fibers such as cotton, and, since it is usually washed in cool water, or only dry-cleaned, the relative impermanence of most natural dyes is less of an issue.
Cotton is less suitable for many natural dyes. As a rule, science fair projects involving natural dyes should be done using wool yarn or fabric, not cotton (though comparing the same dye on the two different types of fiber would make a nice project). There are some natural dyes that will work on cotton, however, especially if mordanted with tannins. Among the better natural dyes for cotton are annato, cutch, logwood, madder, and indigo; all of these except for indigo require mordants, while indigo requires a special type of dye vat.
Synthetic fibers usually cannot be dyed with natural dyes.
There are three major types of natural dyes:
Substantive dyes are used by simply combining the dyestuff, usually in a quantity equal to or twice that of the weight of the fiber, with the fiber (or fabric) and simmering for an extended period of time. An example is turmeric, the spice, which works on cotton as well as on wool; others include onion skins, walnut husks, and tea. Substantive dyes, if made from edible materials, have the advantage of allowing the use of a regular cooking pot for dyeing in; most dyes, even natural dyes, and most mordants, require that a dye pot be devoted to their use, never to be used for cooking again. Another word for a substantive dye is direct; note that there are also a great many synthetic direct dyes.
The vat dyes work the same way on protein and cellulose, by being introduced into the surface of the fiber while in soluble form and then converted into an insoluble form. The vat dyes include many synthetic dyes, but also the natural dye indigo, and the ancient Tyrian Purple dye extracted from shellfish. They are complex to use, requiring the establishment of an anaerobic (oxygen-free) fermentation. See Vat dyes for more information.
Most natural dyeing is done with the use of mordants, most commonly heavy metal ions, but sometimes tannins. (Tannins are particularly important in dyeing cotton and other cellulose fibers.) The mordant allows many natural dyes which would otherwise just wash out to attain acceptable washfastness. A mordant remains in the fiber permanently, holding the dye. Each different metal used as a mordant produces a different range of colors for each dye.
Some of the metals, such as chromium and tin, are extremely toxic. Even copper and iron mordants can be quite dangerous if misused. (Iron is nutritionally necessary, but iron pills are a major cause of accidental poisoning deaths among children.) Alum is the most popular mordant; though less toxic than the other metal ions, it is an irritant, and may be harmful if ingested.
Goodwin's book goes into great detail on the effects of the various mordants on the wool itself, an important matter. Excessive quantities of mordants can be quite damaging to the fiber.
Mordants can be applied to the fiber before dyeing, at the same time as dyeing, or after dyeing. Earth Hues recommend pre-mordanting, as they find they get better colors than when mordanting at the same time as dyeing.
The methods used for mordanting wool and other animal fibers are different from those used for cotton and linen. General instructions on how to mordant various fibers may be found at:
Vinegar, ammonia, and soda ash are not true mordants, but sometimes they are referred to as such by those unclear on the function of mordants. These substances do not stay permanently associated with the dye in the fiber; they serve only to adjust pH, which is a very important consideration in dyeing. Some acids, however, do serve as mordants, most notably tannic acid.
Griffin Dyeworks provides a useful glossary of mordants online, which also includes recipes.
You can dye cotton fabric with metals alone, and no other dyes, by allowing iron to rust while in contact with the fabric, generally using salt and/or vinegar. A potential problem is that fact that the large amounts of metal ions can actually damage the fabric. Do not expect long wear from fabric prepared in this way. Limiting the exposure of the fiber to the metal can control the amount of damage at an acceptable level. Also note that the metal in the fabric can dull scissors and needles used with it.
Earth oxides (dirt!) are used for painting fabric that has been prepared using home-made soymilk, to bind the oxides to the fabric; this technically makes them fabric paints rather than dyes. See instructions for use of earth oxides at Table Rock Llamas. Earth oxides from different parts of the world come in a surprisingly wide range of different colors. (The soy milk must be prepared fresh; when it goes bad, the odors can be spectacular.)
Mud dyeing is more satisfactory as a fun idea than as an actual source of intense color. The ultimate color from simple unmordanted dyeing of cotton with a bright red dirt, after a number of washings, will be a pale buff color. "Dr. Dirt" (Clay Robinson, Ph.D.) explains this in an outline for a student project. He writes that the coloring material in bright red soil is oxidized, anhydrous, Fe2O3, a hematite mineral; that in bright yellow dirt is oxidized, hydrated, 2Fe2O3.3H2O, a limonite mineral, while most dark soils are colored by organic materials. Dr. Dirt suggests testing the effects of soda ash or vinegar, or hot versus cold water, to see whether they affect the color after staining the fabric with the soil.
I like the idea of combining the effects of the various iron-containing soils with tannins, especially on cotton, which tends to dye poorly without tannins. Tannic acid is known to combine with iron, on fabric, into iron tannate, which is said to be a fast (i.e., long lasting) dye on cotton. (This is the basis for the traditional art of African mud cloth dyeing.) The color will be darker, however, rather than reddish. Good natural sources of tannins include tea, 'Tara' powder, oak galls, persimmons, pomegranate fruit rinds, Myrobalan powder; you can also purchase pure tannic acid from some natural dyes suppliers. It is probably best to treat the fabric with the tannins first (such as by "tea dyeing" quite heavily), and then with the mud, to encourage the iron tannate to form in the fiber, rather than in the water.
An alternative approach, to memorialize a location that is important to you, perhaps, would be pigment dyeing with dirt. This means that you would use the dirt as a pigment in a home-made fabric paint, by mixing it with a good lightweight supple fabric paint binder. You might try Versatex Clear Extender for this purpose. This is similar in concept to the use of soy milk as a binder, but with modern materials; the process should be much easier, and the colors more washproof. Heat-set with an iron or in a hot dryer, depending on the instructions provided by the manufacturer.
Books that I recommend on the subject of natural dyeing include Jill Goodwin's authoritative A Dyer's Manual (look for the excellent second edition, printed in 2003, which has been expanded and contains much-needed safety information). Jenny Dean's Wild Color is very pretty and fun to read, but lamentably vague on the issue of which dyes will work with which fibers. Another recommended book is Dye Plants and Dyeing, by John & Margaret Cannon, with detailed information on each plant.
My favorite book on natural dyes is Jim Liles' The Art and Craft of Natural Dyeing: Traditional Recipes for Modern Use, as it contains more different recipes, with more attention paid to historically used dyes and to mineral dyes, and is most clear on which recipes will work on cotton or linen, and which will work on silk, or wool.
If you do not grow your own natural dyestuffs, you will probably need to mail-order them. Dyestuffs should not be gathered from the wild! Lichens, in particular, should never be gathered from nature, because they are extremely slow to regenerate; they cannot be cultivated, either, in spite of some suppliers' claims.
Several good sources of natural dyestuffs are specified on my Sources for Dyeing Supplies page. The Jacquard eColor Natural Dye System includes cochineal, madder, osage, cutch, indigo, a natural wetting agent, and alum as the mordant. Aurora Silks sells a good range of natural dyestuffs. Table Rock Llamas sells a wide range of natural dyestuffs, as well as Earth Oxides.
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