Glass and stone

Excavation

As always seems to be the case, in our last week of the school excavations we have made some of the most exciting discoveries of the season!

At the start of August, we had decided to wind down excavations work in Cutting 3 where the bulk of the burials have been identified*. The plan was to shelve that until next Season, summer 2013, in order to continue with some of the original research agenda for Season 3, to find the extent of the cloister. To that end, Cuttings 6 & 7 were opened to locate the north-east and north-west corners of the cloister. To our relief, they are located exactly where they ought to be!

Cutting 6, facing N; NE cloister corner identified

Cutting 6 is located c. 3 m north of Cutting 3; the north-east corner of the cloister has been identified, along with a bank of material to the east of the cloister wall, consistent with the destruction layers identified in previous cuttings – the 18th century ‘quarrying’ of the building stone.

Cutting 6, facing N; Laura & Ian excavating a sondage at the N end of the cutting

We excavated a sondage (a cutting within a cutting) east-west through this layer, and are hoping to find the wall of the ambulatory – results so far are encouraging as we have a line of large cut stones, slightly displaced but looking distinctly wall-like, and a metalled area, possibly part of the associated walkway.

Cutting 6, facing E; Lucas & Ian discussing stratigraphy

Cutting 7 is located 10m north of Cutting 5, and includes the north-west corner of the cloister. This cutting is slightly smaller than Cutting 6, having been opened just enough to identify the corner, and the surround.

Cutting 7, facing S; Rebecca working on a plan of the NW cloister corner

In both Cuttings 6 & 7 we have identified further architectural fragments in Purbeck marble, probably 13th century, including a beautiful double column base, arcade or window columns and cut sandstone pieces that may have been part of the arcade.

Cutting 7; Purbeck ‘marble’ columns and a double-ended carved column base

More exciting still is the discovery of medieval window glass! While we have identified glass in earlier cuttings, up until now we have only found crumbs of glass. The context in which the glass has been identified is full of lime mortar which is very dry, and not good for glass preservation. In Cutting 6 & 7 however, we have identified substantial glass fragments, with decoration!!!

Conservation

As the glass is in fairly poor shape, we turned to Archaeological Conservator Susannah Kelly for advice on excavating the glass, and conservation requirements. Susannah is based at the lab at the School of Archaeology, University College Dublin and has extensive experience in conserving medieval artefacts.

Susannah Kelly, Conservator (image from http://www.ucd.ie/~archdata)

Medieval glass, when excavated, is very vulnerable to drying out and de-laminating. Our primary aim when excavating the glass prevent it from drying out. So rather than excavating it, and then removing the soil from the glass, we must excavate it in as much of the surrounding soil matrix as possible and keep it damp for transport to the conservation lab. The glass will then require consolidation** using a water-based or acrylic lacquer, to ensure it will not (literally!) fall apart.

Rebecca prepares the medieval glass fragments to be sent for conservation

From the pieces excavated so far it looks as though some decoration survives to we are very keen to ensure that this glass is conserved. Similar or comparable medieval glass from other sites indicate that decoration can survive very well (we had a quick look at some glass finds from recent excavations at Dublin Castle, conserved and looking fantastic)!

Medieval glass fragments – being stabilised for transport using some card, the surrounding soil matrix, and cling film!
Medieval glass fragments – some decoration visible including lines on the large piece and cross-hatching on the smaller pieces – consolidation required to ensure these pieces will survive intact

*excavation may have been wound up but the post ex work on the burials is well under way; student supervisor Siobhan has been merrily managing the cleaning, drying and boxing of the burials, and carrying out some preliminary identification with some interesting results – blog post to follow by the bone-enthusiast herself!

**consolidation is a reversible process, intended to stabilise an artefact, so that it does not deteriorate further, but not permanently altering it.

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About blackfriary

The Irish Archaeology Field School (IAFS) is Ireland’s leading provider of university accredited, site based archaeological research and training. The Blackfriary research project is part of a community archaeology project, based in Trim, Co. Meath. Blackfriary is a 13th century Dominican abbey site; the archaeology includes the buried remains of the medieval abbey and graveyard. Students that participate in the excavation experience and practice all aspects of archaeological excavation processes, learning from experts and leaders in their field, and contribute to an established archaeological research project. IAFS have been excavating at Blackfriary since 2010; students participating have come from all over the works including the Australia, Canada, Europe and the USA.
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