No Lasting Colour Without Alum

Why didn't the ancient Egyptians commonly dye their most often used textile, linen?1 I can't answer that here, but thinking through possibilities, it is said in some publications that linen was harder to dye. This has always seemed unlikely to me. I can dye linen and I'm no expert. Yes, wool more readily takes up the dye but it seems difficult to believe that the ancient Egyptians did not dye linen because it was a little more difficult than wool. Secondly, woad can be used to dye linen blue without the use of a mordant. And, linen has often been dyed with woad, for example labourers' linen smocks of the 19th century were dyed with woad. Woad was used and grown in ancient Egypt. Though using only blue dye is a bit limiting colourwise, unless one is happy with the all-over jean look (tradionally jeans are dyed with indigo, chemically the same as woad). I will look a bit more at woad in the next blog post.

The beautiful vibrant colours of 'Coptic' Egyptian textiles of wool and linen owe themselves not only to the dyes but the mordant (fixative) which ensured that colour did not simply wash out of wool. The wool was dyed whereas the linen was usually left undyed. The word mordant means (bite) and so the colours "bite" and stay fast. In ancient times, as today, alum was commonly used as a wool mordant. Recipes of the time state that wool needed to be washed and then treated with a mordant before the dyeing process. The mordant was alum. In the dyeing process, the mordant is vital, and sometimes more difficult to obtain than the dyes themselves.

Top, alum mines 

Bottom, handspun linen thread dyed by the author using madder mordanted with tannin (from brewers supplies) and aluminium sulphate, and then washed. As can be seen it did fix, it doesn't wash out. However, it hasn't penetrated the thread near the knot. Wool tends to take up dyes more easily. 

But why wasn't alum used for linen? It is possible that alum was hard to get hold of, though by the 1st century AD, when the Coptic textiles were produced, their bright coloured dyed wools suggest that this was not the case.

Alum only occurs as a natural mineral in a few restricted regions. Luckily for Egypt, it was possible to obtain the mineral within the country. Several alum mines have been identified in the western deserts of Egypt; in the Great Oasis at Dakhla and Kharga, and the Small Oasis at Bahariya. These appear as shallow hollows. A specific type of alum was also used to produce a blue pigment in glass making and glazes from the New Kingdom. Pliny the Elder, writing in the first century AD, states that Egyptian alum was highly prized in the Roman world and exported and used as a dye mordant, though Pliny states that it was a wool mordant. 2.

Why was it not used for linen?

Perhaps the important alum resource was deliberately restricted by the government? Alum mines were so valuable that in Roman times they were government controlled. It is not clear if this was the case earlier, but we know that other forms of mining came under royal control before the Roman Period.

Around 2,500 BC, we can see that linen was produced in small factories or workshops. By 1500, if not earlier, it seems that there was a great deal of domestic production with the women of the house heavily engaged in this. Unless wealthy, with connections to the royal family, perhaps they did not have access to alum? It does seem that most of the extant dyed linen comes from royal contexts (Goyon 1996). 

Against the idea that linen was not dyed because alum was restricted, the colours of 'Coptic' Egyptian textiles of the 1st millennium AD show that when given the choice, linen was left plain and only the wool was dyed. But, the amount of colour does not suggest a huge alum shortage. Perhaps, indeed, the difficulty of dyeing linen meant it was usually left plain.

There are alternative suggestions. Perhaps the alum mined in Egypt was the wrong type to be used as a mordant for linen. Alum has several uses and as well as its use as a mordant, it can also be used for tanning leather, as a medicine, and, as stated above, one of the types of alum from with Egypt (cobaltiferous alum) was used to colour glass. Today's dyers of linen tend to use aluminium acetate (it can be bought online), though tannin with aluminium sulphate can be used (see image above). Now the paper by Bogenspeger, below, is great with lots of detail, but perhaps because I'm not a chemist, I'm not sure what types of alum were available within Egypt. Cardon (2007, 21-23) says the type of alum found in Egypt is a hydrated sulphate of potassium and aluminium. Is this the same as the aluminium sulphate one can by from modern dyer's supplies? If anyone can help me out, I'd be grateful. Perhaps the alum which I had used to dye linen is not really so accessible in Egypt and to use other types of alum for linen really was more difficult.

And other suggestions as to why linen wasn't commonly dyed, maybe the Egyptians simply preferred the look of the plain material, and, it had associations of divinity and purity. The ancient Egyptian could appear a very conservative lot, unwilling to change. But, if it works and has important connotations for you why change? 

1. Linen was dyed, for example, linen used to wrap mummies was not infrequently dyed red, and several dyed textiles have been found in the tomb of Tutankhamun. According to Pliny, in the 4th century BC, the generals of Alexander the Great competed in dyeing the sails of their ships. Of course this may have simply been a fanciful story and it is clear that the dyeing of linen was not common. See Goyon 1996.

2. Chapter 52 in his 35th book of his Natural History lists alum uses as: wool dyeing, leather tawing, leather tanning, for creating special metal and glass finishes, for medicinal and cosmetic uses. According to Pliny, alum, ‘… has the effect, also, of checking and dispersing perspiration, and of neutralizing offensive odours of the arm-pits.’

References and Further Reading

Bogensperger, I. 2018. 'Alum in Ancient Egypt: The written evidence', in Antoine De Moor, Cäcilia Fluck and Petra Linscheid (eds.), Excavating, analysing, reconstructing Textiles of the 1st millennium AD from Egypt and neighbouring countries. Proceedings of the 9th conference of the research group ‘Textiles from the Nile Valley’ Antwerp, 27–29 November 2015. Tielt: Lannoo Publishers. pp. 255-263. This can be downloaded from here: https://www.academia.edu/40968832/Alum_in_Ancient_Egypt_The_written_evidence (accessed July 2021).

Cardon, D.2007. Natural Dyes. Sources, Tradition, Technology and Science. London: Archetype Publications.

Goyon, J.-C. 1996 “Le lin et sa teinture en Égypte. Des procédés ancestraux aux pratiques importées (VIIe siècle av. J.-C. à l’époque récente)”, in Aspects de l’artisanat du textile dans le Monde Méditerranéen (Égypte, Grèce, monde Romain). Collection de l’Institut d’Archéologie et d’Histoire de l’Antiquité, Université Lumière Lyon 2, vol. 2, Lyon, p. 13-22