Stained glass – from discovery to conservation

Since 2015, the IAFS has been collaborating with Cardiff University Conservation department, on the conservation of medieval stained glass from the Black Friary excavations.

The stained glass, we believe, was installed during original 13th century construction phase of the friary. It has been excavated over several seasons however, from contexts that were deposited around the time of systematic dismantling (quarrying) of the friary buildings in the 18th century. Excavation thus far suggests that the glass was forcibly removed from the lead cames, possibly hammered out, and most of the lead removed. The glass has survived in various states of repair, from flakes of degraded glass to shards with discernible colour and patterns.

The excavation strategy varies, depending on the size of the deposit; we have excavated individual sherds of glass, caches of glass, and large window fragments that include glass still contained in lead cames. The individual pieces, and caches are recovered by hand into finds trays, and kept cool and damp until all pieces from an individual context or cache are recovered.

The glass is extremely fragile, and is treated with a specific methodology, agreed with the conservation team, to ensure that it reaches the lab in the same condition, as excavated. This includes keeping the glass damp, packing it in sieved soil to prevent further abrasion, and maintaining it in a stable environment until it can be transported to the lab; we have a dedicated fridge in our on-site post ex lab for this.  The glass is also photographed, so the conservation lab has a visual reference to accompany the find record. This helps in planning the conservation process, and in assessing any deterioration in the glass between excavation and conservation.

The window fragments identified are excavated using a ‘block lift’ methodology, designed to allow the excavation and conservation of the fragment in lab conditions. In 2015, conservation staff of the National Museum came to the site to demonstrate this technique: the artefact is isolated by excavating around and below it, leaving the artefact partially exposed and sitting on a ‘pedestal’. Ideally, the artefact is excavated only enough to determine its size, leaving a protective covering of the soil matrix around it. This is then wrapped and sealed with film wrapping (cling film), cushioned with acid free tissue or bubble wrap, and wrapped again to secure this. Finally, this is secured and stabilised by wrapping it with fine gauze bandages infused with plaster – the type used to cast a broken limb! This last bit is a slightly messy process that involves immersing the bandages in a basin of water, and immediately wrapping it around the prepared artefact to ensure that it is secured in place before its starts to dry out. Several bandage wraps might be required to fully stabilise the object. Once the bandages have dried and hardened, the block can then be lifted. This last step requires that the block is carefully levered up, and a prepared board slid underneath it to lift it. Depending on the size and weight of the finished block, this is in then further wrapped, or boxed and sealed, to ensure its safe transport to the conservation lab. When in the conservation lab, it can then be excavated in controlled conditions by the conservation team.

Our first batch of glass was sent to Cardiff, under licence to export and alter from the National Museum, in late 2015. Post graduate conservation students have been working through the collection, and have almost completed the initial conservation, moving now to XRF and SEM analysis. We are really excited to see the finished pieces and to hear the results of the analysis.

Follow the story of the glass on the Cardiff University Conservation Blog, by research coordinator Meredith Sweeney:

What happens when 239 boxes of stained glass and lead are brought to conservators? We buy fridges!

Looking Through the Window Glass

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3 Responses to Stained glass – from discovery to conservation

  1. Denis Shine says:

    Great blog Bairbre. Special thanks to all at Cardiff for their support and great work – especially Meredith.


  2. Frank Scott says:

    Looks like a lot of work…good work..but lots of it

  3. Fascinating to see the process before it came to our lab. Thanks for sharing our blogs!

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