Irish Bloomery Sites: Johnstown I


Metallurgically speaking Johnstown I , part of  the KEK-M4 motorway scheme sites excavated by ACS Ltd. in 2002-2003 (Clarke 2003) was a unique site in terms of the surprisingly large quantities of metallurgical waste  in excess of 2metric tons that it delivered.  At Johnstown I  a number of features have been identified to include smelting furnaces,  hearths and refuse pits and yet more as slag spreads. At Johnstown I , the amount of metallurgical waste is unprecedented for a “primitive” bloomery  site. 

The purpose of SASAA's work is to shed light onto the nature and extent of metalworking activities on the basis of chemistry, mineralogy, and magnetic susceptibility testing between the various excavated features (pits, hearths, smelting pits, grave cuts).


The methodology for the examination and characterisation of the metallurgically related features at Johnstown I  is outlined as follows:

The methodology used for the examination of the metallurgical waste (to include slag, ores, residues  and metallurgical ceramics) is outlined as follows:


The staggering - as far as bloomery sites go, let alone early bloomeries - amount of slag recovered from the site, c.2000Kg, shows a consistent and determined approach towards making iron over two phases,  broadly classified as the Early  (C7th-10th) and Later (C11th-13th)) in an area which must have been designated as iron working and delineated by an enclosure ditch. Such an amount must represent the efforts of a number of people who, either as individuals or as a group, were undertaking to make iron for their own usage or on behalf of some centrally organised authority. The number of knives recovered from the site may suggest a “cutlery centre” but it is almost certain that all sorts of functional artefacts would have been produced there. 

Overall, Johnstown I  is a place where both raw material and artefact were produced, smelting and smithing taking place side by side. In that sense it qualifies as an industrial centre, where the entire process is seen through, from beginning to end.

Aerial photograph of Johnstown I.  Post excavation (ACS Ltd.).

Post excavation photograph of pit F39 (ACS Ltd.).



Soils were analysed by ICP-AES, and their chemical composition subjected to statistical treatment to attempt to identify any trends in the data. Two distinct groups were identified using multivariate discriminant analysis: smelting hearths and non-metallurgical features. The graph above shows the discriminant function (DF) scores for individual samples within the two groups. These groups are quite well discriminated, but there is a small amount of overlap between them. The arrows indicate the ranges of DF1 scores for the two groups.

For full report, click here (SASAA 88)