Bloomeries of the Scottish Highlands
The National Monuments Record for Scotland notes the existence of more than 150 sites of Medieval and post Medieval bloomery mounds. These are small conical mounds or horseshoe shaped mounds of slag associated with bloomery furnaces geographically situated in the Highlands of Scotland. Dated by pottery assemblages and radiocarbon dates between the 13th and 17th century they reflect an industry rich in natural resources (ore and fuel) but also self -reliant, serving a culture proud in its cohesiveness and self reliance.
SASAA has carried out technical analyses of the metallurgical waste from a number of sites excavated in association with GUARD, the archaeological field unit of Glasgow University and as part of a study funded by Historic Scotland (1996-1998).
Excavations at Tamveich Burn, Argyllshire showed that bloomery iron was produced in low shaft furnaces. These furnaces were of the non-tapping type. Excavations at Allt na Caerdach (the burn of the smith), Loch Eck, Argyllshire revealed another type of furnace, rather rare, but nevertheless known, namely the bloomery hearth. given the shallowness of the hearth, it was inevitably being tapped in the course of smelting. The slags showed a high manganese oxide content.
Tamveich Burn excavations (left: SASAA images).
Furnace plan (right: Atkinson and Photos-Jones (1996). The Scottish Bloomeries Project - Interim Report. GUARD 268.2/SASAA 3.6 Internal Report).
While Tamveich Burn, reflects the operations of the "farmer-smith" returning to the locations where he knew he would find his ore and making enough iron to suit his needs, Allt na Caerdach reflects the combined activities of a number of smiths, perhaps hereditary clan smiths working for particular clans. The scale of the manufactories would be expected to be greater as indeed the quantity and quality of their products. No settlements were found in the immediate vicinity of either of these sites (see Photos-Jones et al. 1998; Atkinson and Photos-Jones 1999).
Allt na Caerdach: left: site, right: furnace (SASAA images).
Analyses revealed that the Highland smith relied on sources of iron ore that were renewable, like the iron oxyhydroxides associated with (red) springs-in Highland folklore some red springs (meinn) were renowned for their healing properties. Bog iron ore, also iron oxyhydroxides, rich in manganese and phosphorous, was also utilised. Barium sulphate is another mineral which can be used to fingerprint these ores. The same fingerprinting elements that are seen in slags can also be sought in the slag inclusions trapped within iron artefacts, in this case traditional weapons like the two handed broad sword or claymore. This technique is able to effectively fingerprint artefacts of Scottish origin. The extraction and use of bog and red spring ores reflects not only technological but also cultural practices. Bog ore of one type or another seems to be the predominant source of iron in the Highlands (see Hall and Photos-Jones 1998) as opposed to a much broader range of sources used in the Lowlands.
Contrary to what is often assumed to be the case, self reliance in iron, be it knives or agricultural tools, was the norm rather than the exception throughout much of Scotlland's history. It is almost certain that the farmer doubled up as a smith when the necessity arose, although some farmers may have been more skilled in iron making/smithing than others. Given that the making of the raw material was most likely a skill that many were trained to do -with some being better than others - it is almost certain that the iron making/smithing divide did not exist for most of Scotland's iron making history. (see Photos-Jones 2000). It was not only the Highland smiths who were apparently self sufficient in their own resources, the iron smiths of medieval burghs like Perth appear to have been able to provide themselves with the raw material, thus "bringing down" the divide between town and country. This seems to have been true for access to bog ores (see Photos-Jones and Atkinson 2000).
SEM-BS image of a slag inclusion in an iron bloom from a 13th century context in Rothesay Castle, Isle of Bute.
Dendrites of wustite are shown in a matrix of iron silicate. Metal is ferritic.
Some castle smithies produced their own raw materials.
Scotlandís earliest dated (2nd - 1st centuries BC) furnace was recently excavated by Glasgow University Archaeological Research Division (GUARD) at Tarras farm, in Forres, near Inverness. A box-like furnace (figure below) of the Catalan type appears to have had the air supply directed from above. The slag was viscous and could not have been tapped; it appears highly unlikely that the furnace would have been manipulated. Bloomery furnaces and their associated slag heaps, the bloomery mounds, are a common feature in the rural settlements of the Scottish Highlands, the implications being that, like with all other necessities, iron had to be produced locally. No metal was found associated with the Forres furnace (SASAA Report 40, 1998).
The Forres bloomery furnace ( Will (1998) Tarras by Forres, GUARD 567 Internal Report).