4.14 The Ancient Monuments Laboratory
Technology
Understanding how local resources were exploited is an important part of studies of ancient technology. Recent work in South Lincolnshire has emphasised the area's importance as a major producer of iron in the Roman period. Quantification of this output requires both fieldwork to estimate the quantities of debris used and laboratory-based analysis. The latter, by determining the composition of ores used and slag produced, enables the output sites to be estimated. At Creeton Quarry good quality ore survived on site and a reasonably efficient regime typically produced 61kg of smelting slag and 25kg of bloom iron from 100kg of roasted ore. Using these figures, a total output of 300 400 tonnes of iron during the life of the site can be calculated, and the environmental impact of such a charcoal-demanding industry could be considered. These results contrast with the small scale of ironworking from the Iron Age to Roman site at Thorpe Lee Nurseries, near Egham, Surrey. Iron-rich material, which had been suggested as a possible ore, was found to be too silica-rich to have ever produced iron by traditional smelting methods. However, some unusual iron-smelting slag was found on site, which shows parallels with Norwegian slag-pit furnace technology and demonstrates that smelting was successfully carried out. Analysis showed this to contain high levels of phosphorus, suggesting the exploitation of bog ores.
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An unusual metallurgical study sought to reexamine a 51kg section of an iron beam, excavated from a Roman bath house at Catterick Bridge, North Yorkshire in 1959. The size of the object had required a number of individual iron blooms to be welded together, a crude but metallurgically demanding procedure. The original beam had fractured in use, as a result of oxide penetration, probably after many years in service. The function of the beam is assumed to be as a support for a water-heating tank. Like other beams from Britain and the continent, the iron was found to be largely carbon-free, but contained significant quantities of slag inclusions.
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Evidence for metalworking, in the form of a casting sprue and other manufacturing waste, came from a large assemblage of recycled late Roman lead and pewter from Ickham, Kent. While tableware conformed to previously defined compositional groups, there were examples of alloys that contained only low levels of tin. Such alloys have not often been recorded but might offer certain advantages in terms of mechanical properties, or might represent the recycling of tin alloys with increasing amounts of lead.
The assemblage of window glass from Eynsham Abbey was exceptional in its size and that it could be precisely phased and attributed to a structure. Extensive analysis of over 100 samples has begun to reveal some differences between glass from different phases as well as differences in the glass used in different structures. Glass from some structures appears to show great compositional similarity while that from other structures shows great variability.
Restoration work at Palace House Mansion, Newmarket, recovered the earliest sash window ever found. Analyses of glass from the various panels showed that two types of glass had been used. These compositional differences correlated with the shape (either rectangular or diamond) of the window panes. It is thought that the latter were more frequently used in servants quarters although in the case of the Palace House Mansion window both were used in the same window, although the diamond pane appeared to be a repair.
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The tops from a pair of Georgian side tables, which have recently been returned to Chiswick House, are solid slabs of white statuary marble inlaid with thin veneers of well over 250 geometrically shaped and polished polychrome marbles (a term used here to describe any decorative stone that can take a high polish). This technique is called 'stone intarsia', a form of 'pietre dura', which was popular from the Renaissance period onwards. The many different types of marbles that were used have been identified. It is clear that a large number of the marbles are of classical origin and come from quarries that were long out of use by the Renaissance period; they must therefore have been 'acquired' from the remains of extant Roman buildings. A good example of this is shown in the large central starburst in each tabletop, which is largely formed from Imperial porphyry, quarried from the eastern Egyptian desert. This was a deeply symbolic stone in Roman and Byzantine times, its unique purple colour indicating imperial power and authority. Another 'imperial' stone, the 'granito del foro', is also present in the geometric patterning, along with classical marbles from Greece, Spain, Egypt, France, North Africa, and Asia Minor. Renaissance marbles are also well represented. The eye-catching ribbon border is made from Sienna Brocattello, a rich yellow veined stone. The wide range of classical marbles used, together with what appears to have been an understanding of their symbolism, supports an Italian origin, while [not?] precluding a possible English source of manufacture.
Archaeometry
Environmental Studies
Technology
Conservation