Chemicals for the Primitive Workshop

by Jamie Hall on May 20, 2010

The medieval period covers a huge range of styles and processes, and each of these required different tools and chemicals to be used by the jeweller; the development of specific techniques often depended on what was available locally. In the middle east, the muslim countries were more advanced than Europe, and by the 9th century, they had refined sulfuric acid and various others, including acids from foodstuffs, like acetic acid (vinegar) and citric acid (limes, lemons..etc). This would lead to the birth of chemistry – we might think of it as alchemy now – but it wouldn’t be fully adopted by Europe until the end of the middle ages.

Tartaric Acid

That isn’t to say that Europe was isolated from these new technologies. The Vikings had trade routes with Constantinople and ever further east than that; the Byzantine empire influenced, and traded, with countries as far away as the British Isles. We shouldn’t forget how much the Roman empire created trade routes, and how, even after the empire fell, ships continued to sail the seas. If nothing else, the clergy have visited Rome throughout the existence of the Catholic church, and nobles fought crusades in the middle east for nearly 200 years, bringing wealth, artifacts and architecture back home to western europe.


The historical record includes huge differences in the style and manufacture of jewellery, so the influence of these links should not be overestimated – because a technology like sulfuric acid was available in the middle east does not mean that the Vikings had access to it, even if they traded in the towns where it was made – a product only has value if there is a demand for it. Reading the works of Theophilus, written in the 12th century, pickles and fluxes are rarely mentioned, and the descriptions seem mainly to depend on abrasion to clean up metals. If the european craftsman didn’t know he needed something, the traders couldn’t bring it back for him.

Shellac

In earlier posts, I did some rudimentary testing of pickles and fluxes. Strong acids, like sulfuric or phosphoric acids, are very fast and effective against oxides and fluxes residue. Without them, the process is much slower, but can be done just as effectively with vinegar or lime juice. The availability of citrus fruits would depend on the area, but vinegar was available throughout Europe in one form or another. For fluxes, both borax and boric acid were available in mineral form, so their use seems reasonable. Tartaric acid (above right) is also mentioned in various texts as a flux.


The chemicals can be divided into two groups in my situation – the first are those, as above, that are required by a specific task. The second type are those that are or were common – charcoal, salt and beeswax, for example, which I will have for the purposes of experimentation. I’ve already got a small collection of substances, which include most of the mentioned chemicals, plus water, shellac (pictured above left), lye, rosin and gum tragicanth, and I’ll build this up as time goes by – I’ll get what is easily available, and the rest depends on which processes I want to experiment with.

{ 2 comments }

David Wendelken June 11, 2011 at 02:05

Jamie,

I’ve been reading the new book I mentioned to you (Etruscan Granulation by Nestler, Gerhard and Formigli, Ediberto, Brynmorgen Press, Sienna, 2010). One of the things that struck me was that the method they used to heat up the metal (a charcoal fire with a charcoal “tent” built over the item) would really cut down on the amount of oxygen that would interact with the heated metal. Less oxygen means less oxidation. If they didn’t get all that much oxidation, they wouldn’t need such strong acids to remove it!

I hope to have a period-style forge made by the end of the summer so I can test it out this fall. I intend to do some experiments and see if my theory is supported by results.

Jamie Hall June 11, 2011 at 08:25

The forge sounds fantastic. That is one of my plans, which the residency got in the way of. The “tent” makes sense – Theophilus often mentions laying charcoal “above” the work piece, and I don’t think he means piling it on top of it. Aside from oxidation, you’ll also get a lot more heat inside the “tent” – that was a strategy I was using at Loughborough, because their torches didn’t generate enough heat – I wasn’t using charcoal, just fire-brick, but the heat principle is the same, even if the reducing aspect is absent.

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