(originally appeared in the Clanranald Trust Magazine)

Colour was important to the early Scots. The Romans referred to the Celts’ habit of wearing mantles with small squares in many colours. In the small-scale ‘kitchen workshops’ of the past it must have been impossible to match exactly the colours of what would have been many small batches of wool, and this may help explain why checked fabrics using small quantities of lots of colours were woven. The manufacture of Clan tartans with clearly identifiable colours and designs did not come into being until at least the late 17th century with the advent of standardised recipes, imported chemical mordants, and large workshops. Until that time, particular colour schemes probably had more to do with regionally available dye plants than to clan associations.

In general (but by no means always), the wool and the plant material were layered in the dye pot with or without additional mordant material. The pot was then filled with water and boiled and stirred until the desired colour was achieved. Naturally occurring mordants include urine, wood ash, tannins and crab-apple juice. Today, chemical mordants are used, including metal salts, alum and cream of tartar. Before the advent of alum, staghorn moss was used as a mordant, and the metal salts could be obtained simply by using a copper or iron vessel as a dye pot, or by adding bog-iron or a few rusty nails to the mixture.

Many plants were utilised by the Scots to dye their wool. In the Western Isles, the slow-growing rock lichens were much-prized dyestuffs, and were used to particular effect in the Harris Tweed industry. The generic term for these lichens is crotal, and it was painstakingly scraped from the rocks on which it grew in order to produce a wide range of red and brown hues. Lichen dyes are also supposedly mothproof. Crotal requires no mordant other than a pre-soaking in urine, hence the distinctive and unforgettable aroma of a genuine Harris tweed! Until recently, most homes in the Western Isles would have had a piss-pot outside the door and all visitors were expected to donate generously.

Tormentil, also known as blood root, produces a rich red dye. This was also used as an excellent leather tanning agent, particularly important in those areas of Scotland with few trees such as oak, the bark of which was also a popular choice for tanning. A red dye found in many old tartans has been produced by madder, and it is thought that this was imported, as was indigo for shades of blue.

The roots of meadowsweet, picked in late spring or early summer and soaked in urine before boiling in an iron pot, produce an umber colour. Roots gathered in autumn and processed in the same way give black and, if a handful of sorrel is added to the pot, the result is dark blue. Sorrel, which contains oxalic acid, was frequently added to dye mixes as it helped to fix the dye. The use of an iron pot or the addition of bog iron was important as it contributed the mordant ferrous sulphate to the mixture.

Boiling dock roots in an iron pot could produce dark brown colours. Adding dock leaves to a dye mixture would brighten or deepen the colours produced by the other ingredients. Heather was used for yellows and orange. Using the flowering tops of heather and adding a little alum to the mixture could produce richer hues. Birch leaves and bog myrtle produced a duller yellow. Peat soot, boiled in a bag, was a source of yellowish-brown colours. Berries too were useful dye sources, and a little vinegar added to the mix would brighten the colours produced.

White water lily, common in the lochans of the islands, gives a black dye. The roots of the yellow flag iris, dug up after the plant has flowered, will produce a grey-blue colour. This plant was also used in the past to make ink.

Archaeologists in Perth discovered what appears to have been a 12^th century dyers workshop, with the remains of heather, alpine clubmoss, birch bark, tormentil and bracken, all of which are traditional dye-producing plants.