26 June, 2015

Waste not, want not.

David McIlreavy discusses recent evidence for a previously unrecorded crown glass manufactory in 18th century Rathgar

In January 2015 archaeological monitoring undertaken at Orwell Park, Rathgar in Dublin 2 revealed evidence for a previously unrecorded small-scale 18th century crown glass manufactory. The greenfield site at Orwell Park, measuring c. 30 x 20m, had remained undeveloped despite the relatively intensive growth of housing in the area during the early 19th century. The site had however been heavily disturbed by the insertion of 19th century drainage features, including a stone filled ditch which partially respected the eastern boundary of the property.

This ditch contained a range of ceramic artefacts, mainly attributable to the 19th century; however, at its northern extent a range of 18th century objects were also recovered. This earlier assemblage included ceramics, corroded metal and glass. A concentration of heavily degraded hand-made brick, coal, charcoal and cinder inclusions was also recorded in the surrounding ditch fill. These objects have been interpreted as the remains of a small-scale industrial midden which had been partially disturbed by the later drainage feature. Monitoring did not reveal any further 18th century material or features to the west of the drainage ditch. It was therefore postulated that any potential remaining in situ midden deposits extend to the east and north under the modern road and outside of the current development area.

The artefact assemblage included several sherds of locally made brown glazed ceramics, fragments of probable 18th century clay pipe bowls, some unidentifiable corroded iron objects, some possible slag tap and several pieces of glass. The recovered glass assemblage included a hand blown bottle with obvious extrusion marks on the neck, a fragment of a clear drinking glass, a fragment of glass bullion and two green bottle bases including a possible decanter base. Examination of the cinder and charcoal was not undertaken, but the coal fragments would seem to have been coked to reduce the sulphur released during burning, which would be consistent with even small-scale industrial use.

The most interesting object from this assemblage comprised of the heavily damaged shard of crown glass bullion. The fragment which appears to date to the first half of the 18th century is bluish green in coloration with a very distinctive domed profile, visible in section. The shard measures 118mm x 78mm with a maximum depth in the domed area of 9mm and 4mm in the peripheral edges. The object has been heavily affected by alkali salt accretion and some of the original surface has sloughed due to consistent water exposure. The domed area of the bullion is surmounted by a heavily faceted knob of glass of 28mm diameter.

The name crown glass derives from the mark used by an early London manufactory in the late 17th century however the manufacture of crown glass was a specialised development of the window glass which only emerged in Ireland during the early 18th century. It is produced by hand blowing molten glass into a hollow globe at the end of an iron blow pipe using a horizontal bullion bar to facilitate shaping. After a process of heating, shaping and re-heating, the globe is transferred to a punty rod, which is used to spin the flattened globe in front of a flashing furnace. This encourages the globe to expand, into a large flat disc of almost perfectly even thickness, typically around 1.5m in diameter. The heat of the flashing furnace was responsible for polishing the surface of the glass contributing to its final appearance; a result that was almost impossible to achieve by other means.

The skills required for the handling of crown glass after production were just as specialised. The cutter required knowledge of mathematical angles and a keen eye for the qualities of individual crowns, to avoid wastage of valuable glass. By the 19th century complex diagrams for economical cutting of crowns can be seen in glazier publications. The final panes cut from crown glass discs were known as firsts, seconds, thirds and fourths according to quality. Glaziers usually purchased pre-cut standard pane sizes and grades from a warehouse before going to site. Fixed window panes produced by this process can usually be identified through a ripple effect produced when hit by light. Higher quality bullions were also used in window settings, with the concentric patterning becoming popular in its own right until the 19th century.

In Ireland the majority of the ingredients for high quality crown glass were imported from England and so the majority of manufacturers developed in Dublin near to the quays and usually in conjunction with existing glass manufacturing premises. However, whilst some indication of the scale of the industry in the immediate Dublin area exists, as shown by publications such as the Historic Town Atlas, little specific research into its development has been undertaken.

The glass bullion fragment recovered from the Rathgar site is a particularly interesting example in that it does not seem to have been used for glazing. As noted above the production and subsequent cutting of crown glass was optimised to reduce waste. While the thickness of the glass around the edges of the dome may have been suitable for sale, it would seem that the majority of the artefact may be designated as a waste piece. It is highly unlikely that a waster would have travelled far from the place of manufacture. Also the relative thickness of the glass, even at the ‘saleable edge’, raises the possibility that the Rathgar bullion is an apprentice or tester piece.

There are elements of the bullion which could be considered a production signature. Most obvious is the blue colouration of the glass which may indicate a fairly low iron chemical content within the sand used in the manufacturing process; not low enough for clear glass. This may indicate that the sand was obtained from a local source and not imported as many of the Dublin manufactories used. Whilst the source of the sand used may not be precisely identifiable, the source of the limestone bonding element within its manufacture probably came from the quarries close to Highfield Road in Rathgar. Charcoal for some of the heat processing would probably have been readily accessible from local woodlands that surrounded the site prior to development.

The matter of who would have been responsible for the establishment of such a manufactory in the Rathgar area is another element to investigate. Interestingly Rocque, in his 1760s map of Rathgar (shown above), notes that the site was within the ‘Lord Justices Lands’. The map is certainly of the right date to suggest who would have owned the land during the suggested period of production. However, it is likely that the site was sub contracted to a private individual for the purpose of constructing a glasshouse; designed to take advantage of the expanding Highfield Road on the fringes of Rathgar. It would be interesting to speculate that given that the bullion was mixed with 18th century domestic waste that glass works lived on site as this would indicate a large scale manufactory.

Just how successful such an enterprise may have been remains to be researched however this bullion fragment allows a tantalising glimpse through the looking glass into industrial development on the fringes of 18th century Dublin.

David McIlreavy, Licenced Archaeologist, dmcilreavy@iac.ie


Further Reading

Bailey, F. and McIlreavy, D. 2015 Archaeological Monitoring at 59 Orwell Park, Rathgar, Dublin 2 (Licence Ref.: 14E0380). Unpublished Report, Irish Archaeological Consultancy Ltd.

Douglas, R. W. and Frank, S. 1972 A History of Glass Making. Foulis, London.

Horning, A. and Brannon, N. 2007 Ireland and Britain in the Atlantic World: Proceedings of the Irish Post-Medieval Archaeology Group 2. Wordwell, Dublin.

Hearne, J. M. 2012 Glassmaking in Ireland: From the Medieval to the Contemporary. Irish Academic Press, Dublin.