The Iron Age Soap Experiment

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Soap [Sapo] is also good, an invention of the Gallic provinces for making the hair red. It is made from suet and ash, the best is from beech ash and goat suet, in two kinds, thick and liquid, both being used among the Germans, more by men than by women. Pliny, 'Natural History', Book XXVIII, li

For a long time I have been fascinated by this quote in Pliny about how the Gauls made soap. I have made soap by both the hot and cold process methods using modern lye sources many times, but have done very little soapmaking that requires me to make the lye from scratch as well. For National Archaeology Week 2005 I decided to start an experiment to see if I could make an effective soap based on Pliny's brief description, and then explore whether it does indeed redden the hair or not. This first experiment was not a complete success, for reasons that will become clear as you read through this page, but I learnt a lot doing it and will be repeating the experiment, with the necessary modifications very soon!

The experiment was carried out at the Celtic Village at The Museum of Welsh Life, St Fagans- part of the National Museums and Galleries of Wales.

The first stage was to collect a load of beechwood. Fortunately the woods around here are predominantly beech, so this was easy. I collected what looked like a substantial pile, probably a good meter square of assorted sized small branches and logs of up to three inches across.

This turned into my main mistake of the experiment, it wasn't nearly enough wood. It was also very dry wood and burnt very efficiently, leaving me much less ash to work with than I had anticipated.

The ash was put into a linen lined basket balanced on a wooden bowl , and rain water was poured in. The lye was lowed to drip through overnight. The lye also stripped out some of the colour from the bark of the basket, giving it a brown colour that probably wouldnt have been there if I had been using modern strainers.

Later sources tell us that one way to test whether a batch of lye is strong enough to make lye is to float an egg in it. To give a source of comparison I made up a batch of lye using modern potassium hydroxide (KOH) and water using a computer generated calculation for 500g of fat. As you can see, the egg floats nicely in the clear modern lye, but remains sunk in the brown woodash lye indicating that it is not nearly strong enough by itself.

If I had been able to make more lye (more ash would be needed) I would have reduced the lye by boiling until the egg floated at the same level. As it was, I decided to proceed using a second batch of lye made by running more water through the ashes. I knew this would be too weak for really successful soap, but I hoped to be able to learn from following the experiment through to its conclusion rather than stopping early. A second problem now arose because my supplier of goat fat had delivery problems, so I chose to proceed using pig fat (lard), and plan to repeat the experiment in a few weeks time using lye of the correct strength and the right fat. Below you can see the lard being melted, the lye being poured in, and the mixture at the first stir. Looks appetising doesn't it!

One question which I hope to address in my next attempt will be that of what container the soap might be made in. Pottery seems the most likely, but bear in mind it would be unglazed at this period. A bronze cauldron is unlikely based both on the relative expense and rarity of these compared to pottery, and the practical fact that bronze reacts with tin. I settled on an enamelled pan for todays approximation, but I am very aware that it does not accurately reflect the likely reality. After one hour of gentle heating, soap bubbles have started forming on the top of the mixture. I was really pleased with these! There is clearly too much fat to lye in this batch, but after three hours the mix is still staying as one reasonably homogenous whole.

Reducing the mixture down initially looked promising, a thick scum of soap was forming on the surface, and the smell was exxactly what I would expect from a hot processed batch of soap. However, an hour later, all the surplus water has been boiled off and you can quite clearly see that I only have a small scum of soap on top of an otherwise bland pool of molten fat. Up until the last hour the pH reading had been up at 10 or above (the raw lye read 11 on my universal indicator papers), but the finished soap had exhausted the alkali and left me with plain fat with just a little soap on top.

In conclusion, I'm not at all desponant that I didn't make a full batch of soap using methods plausible to the Iron Age. I knew as soon as the ash had been prepared that I had far too little to make a proper attempt, but by continuing I learnt a great deal about how the cooking process differed from a batch done in a controlled kitchen environment, and I am very hopeful that my next attempt, with stronger lye, and goatfat in accordance with the original quote, will be much more successful. I will update this page as soon as I am able to once the next experiment is complete. In the meantime, I'd love to hear from anyone who has attempted a similar experiment useing beechwood and goat fat. Sally. July 2005

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