Are Natural Dyes Safe? Clearing up the Confusion About Chemical Dyes and Metal Mordants

Who says natural dyes aren’t safe?

One of my friends said that she wasn’t going to learn to use natural dyes because of the heavy metal mordants that you have to use with them. My friend had heard that natural dyes were toxic and polluted the environment.  I saw a similar discussion about natural dyes on the website of a manufacturer of chemical dyes several years ago.  What this manufacturer failed to reveal was that all dyes, both natural and chemical require some kind of metal or salt to make the dye permanent on the fabric.

Mordants bite

When you want to dye cloth or fiber with natural dyes you will need a mordant to help the natural dye chromophores bite the natural fibers, to make a colour fast dye.  Without mordant many natural dyes will just wash out because they have nothing to hang on to.  Chemical dyes also need mordants to help them stick to the fibres, but chemical dyes come to the dyer with the heavy metals already in powder form in the dye bottle, along with the dye powders.  The mordants used with chemical dyes are much more toxic to humans and the environment than the mordants that most natural dyers used.

Heavy metals in chemical dyes — don’t drink me

Cadmium, lead, chromium, tin are just some of the heavy metals used in chemical dyes.  They don’t need to be listed on the label.  So you won’t know you’re are being exposed to them unless you buy dyes in large enough quantities that they come with a materials safety data sheet.

In powder form, all chemical dyes, including food colourings (Koolaid powder, jello powder) should be treated as hazardous chemicals and you should protect yourself with an appropriate mask, gloves, clothing and skin protection.  In liquid form, weak-acid dyes are fairly benign but still contain metal salts.  Wear gloves when handling them.

Weak acid dyes are the most commonly used on protein fibers like wool, mohair, and silk.  Weak acid dyes exhaust at temperatures between 160F and 180F, depending on colour chemical. Once the dye bath is exhausted, the dye liquid can be neutralized with baking soda and disposed of on the ground or down the drain.

The metals and dye chemicals will be on the fabric or fiber once the dye bath has been exhausted.  They will be absorbed by your skin and they will wash off the cloth and down the drain a little bit at a time over many wash cycles.  But in a single dose, they are considered benign.

On the other hand, Fiber reactive dyes, the kind of dyes used on cotton or linen, are toxic in powder form and when liquid.  They adhere to a fabric in cold temperatures because of a chemical reaction between the mordant, the fiber and the dye molecules and need to be “batched” for a certain length of time in order to set.  These are the dyes most commonly used on cotton and linen fabrics.

Wear a hazardous materials mask (not a dust mask), gloves and protective clothing, including goggles, when you are working with these dyes and dispose of the dye bath as you would any toxic material.  The dye bath is not benign once the dyes are exhausted, in the case of fiber reactive dyes.  Exposure can lead to skin irritation, irritation of mucous membranes and even organ damage with heavy exposure, such as with textile workers.

Traditional natural dye mordants with a capital Pee

Traditionally professional natural dyers used chromium and tin, along with the less toxic mordants — alum, copper, and iron, as well as stale urine.  Today chromium and tin are known to be dangerous and toxic to the dyer and the environment even in micrograms and natural dyers do well to avoid them.  Many beautiful, vibrant and permanent colours can be achieved with using only alum, with after-dips in rust water, to sadden the colour, or copper water (copper pipe left to sit in an ammonia solution.)

Urine has a strong ammonia odour from the urea dioxide and nitrous oxide in it.  It can be beneficial when dyeing with indigo or woad, especially.  But dye with it outside and away from human dwellings.   Urine can also be used as a mordant for other natural dyes.

My favourite natural dye book, A Dyer’s Manual by Jill Goodwin, (brought back into print) has more information if you’d like to explore this free source of dye adjunct further.  There are lots in this book about working with children and the textile arts, too.

Safe and Experimental mordants:

Further, experiments are being done in Turkey (with the Dobag project) using calcium and magnesium salts as mordants.  If you have hard water, and calcium, magnesium or iron salts in your water, it will affect the colour of your natural dye and act as an adjunct with your other mordants.  Calcium increases the brightness of the colour — especially with yellows, greens and madder reds. And in Australia India Flint is experimenting with natural seawater, which contains many salts, including alum, as a mordant.

Less is more when it comes to mordants:

With mordants, less is more.  While many of the older natural dye books from the 60s and 70s recommended up to 25% alum by weight of fiber (wof), using only 7 to 10% alum with 3 % cream of tartar gives permanent and vibrant colour without the damage common in excess alum use.  This translates into 2 to 3 tablespoons of alum and 1 tsp of cream of tartar per 1 lb. (450 grams) of yarn or loose fiber, for wool or other protein fibers.

Using iron and copper to shift the colour

I use iron and copper mordants only as an after-dip at the end of the dye period.  Iron can be achieved, without exposure to iron dust, by soaking iron rail spikes, iron nails in a water pail to which a 1/4 cup of vinegar or 1 tbsp of citric acid has been added.  Dip the wool for only 5 minutes and rinse.  The colour will sadden, giving greenish yellows, bolder greens or rusty reds.  Dyeing in an iron or a copper pot will also shift the colour.

Iron is most valuable to achieve blacks on fiber when using a tannin-rich plant like a bark or mullein.  Since iron can damage fiber with time, use it sparingly.

Safe natural dyeing is achievable

Natural dyers have many options for achieving permanent colours without exposure to dangerous toxic metals, while chemical dyers are often exposed to heavy metals without their knowledge.  The full knowledge of natural dye mordants has not yet been reached.  Each dyer can have the joy of their own experiments with locally available materials to achieve a  beautiful, bioregional colour palette.  Remember to keep a dye journal, so that if you get an especially attractive colour you will be able to repeat it at will.

Your Turn:

What is your favourite mordant to use with natural dyes?  Leave a comment.