Using Plant Dyes

How to apply vegetable colours to wool

The following instructions do not apply to woad or other indigo dyes. See the woad page for how to use that plant.

There are probably as many recipes for applying plant dyes as there are dyers, so please view the following as just a guide. The information is intended as a starting point, from which you can begin your experiments - and experimenting is more than half the fun!

Please take care and use common sense, as the dyeing process involves potentially hazardous chemicals as well as large quantities of very hot water. Mordants, most of which are salts of heavy metals, are an obvious hazard, but the dye plants may also be hazardous - just because it is "natural" doesn't necessarily mean it is safe. Also, some people have allergic reactions to certain plants. You should avoid skin contact, avoid breathing the fumes, and work in a well-ventilated place. Chrome mordant is particularly toxic and should not be used in the kitchen.

It is customary in dye recipes to state the amounts of chemicals as a percentage of the weight of the wool. For example, if you were dyeing 100 grams of wool and the instructions specified 5% alum, you would use 5 grams. You will see that the calculations are easier if everything is measured in metric.

Equipment

Everyday kitchen utensils can be used for dyeing, but they should be kept solely for that purpose and not used for food preparation.

You will need a metal pan or bucket in which to boil the dye liquor. Preferably, the dye pot should be stainless steel or enamel. Copper, iron, aluminium or ordinary steel can be used but they will affect the colour of the dye, because the metal will mordant the wool to some extent.

The size of the dye pot will obviously determine how much wool you can dye in one go. I recommend that the liquid-to-wool ratio for yarn should be not less than 100:1. This means that a pot that safely holds 5 litres (allowing headroom for foaming and bubbling) could be used to dye 50 grams of wool yarn. If dyeing loose wool, the ratio should be at least double that. The wool is more likely to felt during dyeing if it is cramped in the pot.

The dyepot should have a lid of some sort, to save energy while raising the temperature of the liquor. You will probably want to monitor the progress of the dye, so a glass lid is a good idea.

A stirring rod is needed for removing yarn and gently moving it in the dye liquor. This could be a short length of dowel, a length of stainless steel rod, or maybe a large nylon or wooden spoon. A measuring jug, old jars and several plastic 5ml. spoons will be needed for measuring and mixing chemicals.

To be able to determine whether your dye bath is acidic or alkaline, you will need some pH indicator paper strips. These come in little "books" with a printed scale inside the covers, against which you match the colour of your test strip. Some dyers use an electronic pH sensor, but these are quite expensive for occasional use, and they have to be calibrated using a specially prepared buffer solution.

A set of scales will prove useful for accurately weighing wool and dyestuff. To measure chemicals accurately, you would need scales that can weigh in grams. Lacking such accurate scales, many dyers measure the chemicals with a medicine spoon (see approximate weights, below) or mix bulk amounts in water and measure the solution. For example, you could dissolve 100g. of alum in 5 litres of water, then if you need 5 grams you would measure out 250ml.

It is sensible to wear rubber gloves and an apron, and use a dust mask when you are handling powdered dyes and chemicals.

Mordanting

Most dyes derived from plants do not have great affinity for wool: on their own, the colours they produce may be pale, wash out easily or fade quickly in sunlight. In order to improve the colours and make them more permanent, vegetable dyes have to be combined with a metallic element. In practice, a metal salt, known as a mordant, is applied to the wool before dyeing.

There are notable exceptions to this. Woad (and other indigo dyes) are applied in an oxygen-reduced dyebath, the dye being fixed by simply removing the wool from the vat and airing it. Some kinds of lichen, bark and nut hulls contain acids which act as a mordant and they can produce reasonably fast colours on their own, although different shades may be obtained by applying a metal salt mordant.

Mordants

The most commonly used mordants are salts of aluminium, iron, chrome and tin. Oxalic acid and tannic acid are also sometimes employed, but these are more commonly used on vegetable fibres.

Most home dyers mordant with aluminium potassium sulphate, known commonly as Alum. This salt has been employed for centuries and is a popular choice today because it is relatively non-toxic. Also, alum doesn't noticeably add any colour of its own to the wool (maybe a slight yellowing), unlike some other metal salts.

To reduce the possibility of damage to the wool caused by the alum, most dyers also use Cream of Tartar (potassium hydrogen tartrate). Cream of Tartar is an acid salt, which works as a buffer: it prevents the liquor from becoming too alkaline and helps the alum to dissolve.

The standard rate of use is 10% alum with 4% Cream of Tartar, but anything from 8 to 25 percent alum is common practice, with 3% to 5% Cream of Tartar.

Iron (in the form of ferrous sulphate) is used mainly to "sadden" the colours obtained with other mordants. It always produces drab shades and is useful for obtaining dark brown or black from tannin-rich dyes. It should be used sparingly, however, because it can make wool harsh and brittle. I recommend using not more than 2%. A traditional method of making your own iron mordant is to soak rusty nails in vinegar. The problem with this home-made mordant is that you don't know how much iron you are using.

Chrome (usually potassium dichromate) is the mordant normally used in industry, but shunned by many home dyers because of its toxicity. A very small proportion of chrome is needed, compared to alum and it has a beneficial effect on the texture of the wool, leaving it soft and silky. Use from 1½ to 3 percent.

Copper mordant generally gives darker shades than those obtained from the same dye with alum and often gives greenish hues. Normally employed in the form of copper sulphate, it is used at from 3 to 5 percent.

Tin gives very bright shades (the scarlet coats of guardsmen used to be dyed with cochineal on a tin mordant) but the mordant, stannous chloride, is very expensive. Use at 3% and also add 12% Cream of Tartar, because otherwise the wool can be left damaged, with a harsh texture. Small amounts of tin may be added when dyeing on an alum mordant, to brighten the colours.

How to Apply Mordants

The wool should be clean and thoroughly wetted-out. If you have difficulty in completely wetting the wool, add a spot of detergent to the water. Fill the dye pot with water. You can start with hot water from the tap, so long as the temperature is below 40 degrees celsius.

Measure the required amount of mordant into a jar or small bowl, then add boiling water to dissolve the chemical. When the mordant is dissolved, pour the mordant solution into the dye pot and give it a stir. If you are using Cream of Tartar, dissolve that in the same way and add it next.

Time and temperature are crucial factors in dyeing. Heat provides the energy for the chemical reactions to take place and the hotter your dye vat the faster the reactions occur. To achieve evenly dyed yarn, the temperature should be raised very slowly. It should take at least 30 minutes to rise from 40 degrees to simmering point; most professional dyers allow an hour. This will give time for the chemical to distribute itself evenly in the wool before it is fixed by the heat.

So raise the temperature of the mordant very slowly to simmering point, then allow it to simmer gently for 40 to 60 minutes (30 minutes when using iron mordant). After this time, turn off the heat. Allow it to cool slowly back to room temperature, leaving the wool in the mordant bath until next day if you can spare the time. The exception to this is when using an iron mordant: don't leave your wool in an iron mordant bath after the simmering time is up - remove it and let it cool quickly.

Rinse the wool a couple of times to remove any mordant that hasn't attached to the fibre. You can then proceed to dye the wool, or dry it for dyeing at a later date.

Dyeing

Most people extract the colour from the plant material, then remove it from the pot before adding the wool. This is the method I describe here. However, some dyes work better if the wool is put in with the plant, so you may like to try that. The plant material should be chopped into small chunks. Some dyers put the dyestuff in a fine-mesh bag.

If you are using dried dyestuff or hard materials like bark or wood chips, soak them before use. You will learn from experience how long to soak; barks usually need at least 48 hours (and may benefit from soaking a week or more); softer material, such as Golden Rod, will only need a few hours.

Place the plant material in your dyepot (together with the soaking water, if relevant) and add enough water to cover it. Simmer the dyestuff for about half an hour or until the water is sufficiently coloured, then sieve the dyebath (unless you used a mesh bag, of course).

Allow the dye liquor to cool down to below 40 degrees celsius before adding the wetted-out wool. Begin to raise the temperature very slowly. It should take at least 45 minutes to reach simmering point. Hold the temperature at a simmer for about 20 minutes, or until sufficient colour has been taken up by the wool. Move the yarn gently in the dye bath from time to time, in order to achieve even dyeing. Don't let the dyebath boil ferociously or the wool will probably felt.

You can either remove the wool straight away, or leave it to cool in the dyepot. Then it should be rinsed several times to remove loose dye before washing it carefully.

There is often enough colouring matter in the dye liquor to dye two or three lots of wool, so it is useful to have several skeins pre-mordanted in readiness. Make sure you allow the temperature of the dyebath to drop below 40 degrees celsius before adding the next lot of wool, to avoid blotchy dyeing.

The above is a general method for using plant dyes, which is open to a hundred-and-one variations. A small amount of ammonia improves the colour of some dyes, others are better with a drop of vinegar. Some dyes take longer to fix to the fibre, others much less time. Don't be afraid to experiment - and keep notes of what you do!

Table of Approximate Measures

Chemical	Weight of 5ml. (level teaspoon)
Alum	5g.
Cream of Tartar	4g.
Copper Sulphate	6g.
Ferrous Sulphate	4g.
Stannous Chloride	8g.
Potassium Dichromate	8g.
Sodium Bicarbonate	5g.