Certainly not! Not in every case, that is.
It's funny how many people think that "natural" means almost the same thing as "safe", as though they'd never heard of poison ivy or deadly mushrooms.
Some natural dyes are almost perfectly safe; others are quite toxic. Some synthetic dyes are safe even to eat; others are too toxic to bring into your home.
Logwood, for example, is a lovely natural dye, capable of creating a surprising range of colors, depending on the mordant used, including violets, blue-grays, and the best natural black. However, the active ingredients, hematein and hematoxylin, are toxic whether inhaled, absorbed through the skin, or ingested. It can be used safely with the appropriate precautions, but is not to be used carelessly. As much care should be taken with this natural dye as with any of the common synthetic dyes we use. Unless a given dye, natural or not, has been tested for safety or is commonly used for food, it is important to follow these same precautions. Wear gloves, don't breathe the powdered form, and never reuse a dyeing pot for food preparation!
Other dye-plants can be more dangerous. Bloodroot, lily of the valley, rhododendron and azalea leaves, privet hedge trimmings, yellow flag iris rhizomes, and larkspur or delphinium flowers may be toxic to the user of the dyed material, and yet none of them is a sufficiently excellent dye to be worth any danger, according to Rita Buchanon. In her excellent book, A Weaver's Garden: Growing Plants for Natural Dyes and Fibers, she detailed her experience with bloodroot:
Of course, many natural dyes are quite harmless. For example, cochineal, an incredible natural red dye which you can mail-order, is often used to color foods such as fruit-flavored yogurt.
Most natural dyes are not particularly toxic in themselves, but they will not stick to fabric unless a mordant is used. Typically, a mordant is a heavy metal. Heavy metals are extremely toxic, and bad for the environment, as well.
Alum is a relatively safe mordant that is often used with natural dyes. It is any of several chemical compounds based on aluminum, which (in spite of the silly claims about Alzheimer's disease, which is not caused by aluminum) is much safer than chromium and other heavy metals. However, even alum has been known to kill people! The fatal dose of alum is 30 grams for an adult; the fatal dose for a small child is, of course, far less, depending on body weight, perhaps as little as 3 grams. Doses that are too low to kill may still cause irritation or more serious health problems. Do not be misled by descriptions of "food grade alum". The fact that tiny amounts of alum are used in pickles which are intended to be eaten in small quantities does not show that alum is safe in dye-use quantities. Always keep all mordants well out of the reach of children. Alum can be used safely as long as small children or others who might be inclined to eat your materials are not present, and if the material mordanted with alum is not given to babies or others who might chew on the fabric.
Somewhat more dangerous mordants are copper and iron. Either can be deadly, and should not be used around children, but they are safe to use if you follow all of the required safety precautions. Iron is toxic in overdose (according to the United States FDA, iron is the leading cause of poisoning deaths in children under 6, despite child-resistant packaging), but it will not harm the environment when disposed of. Iron is not only a mordant for other dyes, but can be used as an interesting dye in its own right, by applying bits of iron metal to fabric and allowing them to rust. At least it does not poison the ground if you pour this mordant out on it.
Chrome mordant, in contrast, will poison the ground, and it has caused many serious injuries or deaths among workers exposed to it. It is a known human carcinogen. I recommend against any use of chrome, including potassium dichromate and potassium bichromate (two names for the same chemical), as a mordant. Chrome can produce very bright yellows, but it is not worth the risk of cancer, other illnesses, and even death.
Tin mordant is not recommended for beginning dyers, but can be used with care.
When using natural dyes, be careful to research the safety of your dyes and mordants!
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