{"id":1889,"date":"2015-03-06T20:21:55","date_gmt":"2015-03-06T20:21:55","guid":{"rendered":"http:\/\/userblogs.ganoksin.com\/primitive\/?p=1889"},"modified":"2015-03-06T20:21:55","modified_gmt":"2015-03-06T20:21:55","slug":"choosing-metalworking-fluxes-medieval-experimental-archaeology","status":"publish","type":"post","link":"https:\/\/userblogs.ganoksin.com\/primitive\/2015\/03\/06\/choosing-metalworking-fluxes-medieval-experimental-archaeology\/","title":{"rendered":"Choosing Metalworking Fluxes – Medieval Experimental Archaeology"},"content":{"rendered":"

For many metalworking experiments, fluxes are required. Typically, fluxes are liquid at the working temperature of the process, have a lower density than the molten metal, and prevent the formation of metal oxides. These characteristics allow molten metal to flow, and to avoid reactions with atmospheric gases \u2013 fluxes are particularly important in the case of soft and hard soldering, where oxides and solid debris will interfere with capillary action. $\"Salt$ <\/a><\/p>\n

Hot processes are more efficient if flux is used, but fluxes are not ubiquitous. By avoiding an oxidising atmosphere (air), the need for fluxes is reduced; charcoal-fuelled hearths provide a reducing atmosphere, while crucibles that are deep-bottomed, narrow-necked and\/or lidded present less surface area and gas volume.<\/p>\n

That said, any workshop using hot processes should have some fluxes on hand \u2013 but which to choose? A modern workshop might have borax as a general purpose flux, and other specific types, depending on the metals they work with. There is a wide range of suitable materials. The medieval workshop was much the same, but local availability and trade links would limit their options.<\/p>\n

Theophilus, writing in the early 12^{th<\/sup>C, is thought to have been a monastic metalworker, which is supported by the liturgical focus of On Divers Arts<\/i>. If he was Roger of Helmarshausen (this is not certain), then he was describing an inland European tradition, with some imported materials. Waxes and resins are used for soft soldering, while argol<\/i> and salt are used for hard soldering and casting. All of these can be obtained from food production and land management, eg. Argol<\/i>, which is described as “the substance that accumulates on the insides of jars in which the best wine has lain for a long time” [III-31]. This could well be potassium bitartrate, and the translators suggest “crude potassium carbonate” when the argol is burnt.<\/p>\n}

There are other fluxes des $\"molten$ <\/a>cribed, but these are somewhat different \u2013 litharge fluxes the cupellation process [III-23], and finely ground glass is added “…if you see the silver boiling and jumping out…”. The litharge flux is there to aid the formation and movement of metal oxides into the cupel. There is a tantalising mention of “the resin called borax”, but it is unlikely to be the modern material – the translators suggest the Arabic word baracha<\/i>, but point out that borax would be unsuitable for applying niello, [III-29].<\/p>\n

Overall, the text is very consistent, which puts in stark contrast to the older metalworking texts, principally Leyden X<\/i> and Mappae Clavicula<\/i>. Unlike the European context of On Divers Arts<\/i>, these form a corpus of recipes collected over centuries, and from several locations in the southern and eastern Mediterranean (and beyond). This is reflected in the confusing array of fluxes described. The hot, dry climate provides different opportunities, including efflorescent deposits of mineral salts like natron. As the materials vary, so too do the names for them, and a thorough examination will have to wait for a future blog article.<\/p>\n

For European contexts, the argol<\/i> and salt of Theophilus seem reasonable for high temperature processes, and exotic materials are best avoided. That said, there would be other fluxes available (Europe is a large geographical area), and research and experimentation should be done individually for each context, reflecting local conditions.<\/p>\n","protected":false},"excerpt":{"rendered":"