Message: Dear Dr. Paula,

My daughter’s 7th grade project is to make dyes from edible materials (fruits and vegetables), and see how they behave on different materials (cotton, silk, wool and synthetic). Under the umbrella of Natural dyes, you list substantive, vat and mordant dyes. Are the dyes she’s likely to be making in our kitchen all substantive?  If not, is there any simple chemical assistant that might be more accessible than a heavy metal ion that she might add to her “edible” dyes to produce a brighter, more color-fast product? (She won’t actually be washing any of the fabrics.) Thank you for your site.


There are a few natural substantive dyes that will work without mordanting. Restricting yourselves to these dyes limits the possible color choice and how long the dyes will withstand washing, but it will simplify your project. Some examples of dyes you can use this way are turmeric, saffron, safflower, annatto, and black walnut hulls. Cochineal is a natural insect dye often used to color foods and cosmetics; to dye cotton or linen with it, you must use a mordant, but it will work on wool and silk and even nylon without a mordant. (Note that nylon is far easier to dye than polyester and can be dyed with many more natural dyes than polyester can.) The problem with cochineal is that it is difficult to find, unless you mail-order it from a natural dyes supplier such as Aurora Silk. Turmeric is the most readily available and least expensive of the natural dyes which do not require a mordant; you can find it in the spice aisle at the grocery store. Saffron is similar to turmeric but far more expensive. Annatto is a seed used in Latin American cooking which may be more difficult to use than powdered turmeric, since it is less soluble in water. Walnut hulls are readily available only if you have a walnut tree nearby, but you can also use the hulls that surround pecan nuts or butternuts on the tree (the outer hulls have been removed from the nuts in the shell that you see at the store).

The majority of natural dyes are mordant dyes, which means that fabric or yarn to be dyed with them must be pre-treated with mordants. There is one mordant that you can use that is reasonably safe, which is alum. Alum is dangerous only for children too young to understand that they should not eat their chemical materials. Most seventh graders should be able to use alum mordant safely, with adult supervision. All natural dyes found in your kitchen require the use of heat, which is more likely than alum to be a hazard, due to the risk of a scald injury. It is a good idea to simmer each of your test pieces of fabric or yarn for half an hour or longer with a large amount of the dyestuff, preferably twice the weight of your fabric or yarn. A handy way to dye several items at once without spoiling your cooking pots is to use quart-size glass jars which you place in a cooking pot that is partly filled with water. 

Without mordants, most natural substances will make poor dyes. Even with a mordant, many naturally colorful substances make very poor dyes, since a dye must be not only colorful, but also able to form a long-lasting bond to the fiber. The purple anthocyanin color from grapes or cabbage will turn dull, while the green of chlorophyll from any leaf will turn brown. In order to avoid disappointment, I recommend that you select at least one dyestuff from my list of good substantive dyes above. A favorite subject for natural dyeing projects is beets, which make such a lovely red cooking water that everyone assumes they must be a good dye. In fact, beets are an extremely poor dye. The red coloring washes out the of fabric, leaving at most a boring beige or tan. It can be fun to compare them to substances that are good dyes, such as turmeric or cochineal. See "Beets as a natural dye". 
 
Even substantive dyes such as turmeric may work better with the use of a mordant. When my son was in eighth grade, he used a number of dyes, natural and synthetic, to dye various fibers for a science fair project. He boiled his swatches of fabric in the alum and then, after rinsing, in the dyes, for half an hour each. When he used turmeric, he found that the polyester which had been mordanted with alum took the dye, turning a nice yellow.  See "Turmeric dyes practically everything!", and "Cochineal is a fine dye".

Some natural dyes will change color if you use an acid, such as vinegar or cream of tartar (which is tartaric acid), versus the use of a base, such as baking soda or washing soda. Acids brighten the color of berries and grapes, but they hasten the browning of green chlorophyll. Neither acids nor bases will act as a mordant.

In order to make a good test of any textile dye, you must wash the fabric after applying the dye. Dyes that have not been tested by washing might not be dyes at all, merely temporary stains. A dye that resists washing is useful, while a temporary stain is not at all useful for fabric or yarn. There is no need to wash your test swatches in the washing machine; you can wash them by hand in the sink. Hot water is a more significant test than cool water, since many poor dyes will wash out in hot water but not cool water. For my son's natural versus synthetic dyes project, he choose the easy alternative of rinsing his fabric swatches in the sink, then placing them in a lingerie bag and washing them in the washing machine. The lingerie bag was necessary in order to prevent the small swatches of fabric he used from disappearing down the drain.


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