Keeping a lid on it

By marketing on 4 Jul 2012
Fig. 1 The coffin lid as it was displayed at St Bride’s (underside visible)
Fig. 1 The coffin lid as it was displayed at St Bride’s (underside visible)

After our recent Initial Investigations blog post, Jill Saunders tells us more about the conservation work on the iron coffin from St Bride’s, this time focusing on the coffin lid.

The lid of the coffin had key features relating to the object’s anti-theft function with iron pegs all the way around which would spring and catch under a ledge on the coffin base, keeping the casket locked tight. Though the main pegs were quite robust, the catches were more vulnerable and we had to be mindful of them during treatment and any manoeuvring. In addition to small corroded losses and a build up of corrosion products (which would be expected), the lid displayed signs of damage appearing to be caused by force. There was a missing peg revealing a circle of fresh iron and potions of the sheet metal were caved in and curled round. Though we cannot be certain how or when this damage occurred we suspect that it was caused at the time of excavation or shortly afterwards by archaeologists forcing the coffin open. The peg could have also been knocked off at a later date. Eg moving the object around the tight paces and stone walls of the crypt.As mentioned in my first blog, Conservation Introduction, we knew that this object had to be prepared for display and then long term storage back at the crypt so we were concerned with its general appearance and aesthetic features and wanted to offer some protection against wear and tear and environmental conditions. After preliminary dust removal using a brush and vacuum, there remained a great deal of unsightly bulbous orange/brown iron corrosion products which disrupted the flat surface and obscured manufacturing features such as join edges, rims and the pegs too (Fig. 2). In order to minimise the risk of damage it was important to approach the object with the least possible force and work up until a successful result was achieved. We began simply brushing and found that stiff brushes were able to remove a significant amount of the very bubbly upper-most corrosion.

Fig. 2 Bulbous corrosion products along the inner lid rim

Fig. 2 Bulbous corrosion products along the inner lid rim

 Fig. 3 A region of the rim where bulbous corrosion has been removed

Fig. 3 A region of the rim where bulbous corrosion has been removed

However some lower levels were more stubborn. We used a type of rubber named Garryflex which contains abrasive grit to work more on these areas and the action also helped to reduce the pale corrosion dust created by the brushing which was trapped between the crevices of the uneven surface.

Fig. 4 Garryflex rubber blocks

Fig. 4 Garryflex rubber blocks

 Fig. 5 A portion of the coffin lid inner surface with corrosion brushed and Garryflex abrasion

Fig. 5 A portion of the coffin lid inner surface with corrosion brushed and Garryflex abrasion

Because of the pegs, the lid had been placed on its board front side down with the inside cover visible and pegs sticking up. However from brief visual examination during transportation we knew that the other side had some traces of decoration. We were hence careful not to press down too hard and tried to minimise movement in the object during our corrosion reduction on the inner lid.

We reached a point where we were making little difference to the appearance of the object so that the possible damage to the outer side by vibrations of the cleaning action and amount of time spent reducing corrosion could not be justified to continue work. We did consider using a harsher abrasive such as sand paper to further wear down remaining compacted corrosion products which caused irregularities in the surface but this seemed unnecessary. We were happy with the appearance achieved, having removed the orange/brown bulbous pale corrosion which is generally considered undesirable. It was not our intention to remove all signs of degradation from the lid as its age and history were fundamental to its perceived values and its status as ‘archaeological object’ admits imperfection and signs of object biography. Also we wanted to avoid risk of revealing fresh metal as this would be unsightly and could create active corrosion cells. Though we felt that we would want to lacquer the object and this side was now ready for that process, we were concerned for the features on the outer side and wanted to investigate and secure them ASAP.

Watch this space for the next entry covering the outer side of the coffin lid with decorative remains: Turning over a new lid.

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