Conserving the unique Porphyry Bowl at Anglesey Abbey

15th December 2017

Our Norfolk Workshop has completed works to the rare Egyptian Porphyry Bowl at National Trust’s Anglesey Abbey, near Cambridge.  

Earlier this year Cliveden Conservation was appointed by the National Trust to carry out work to the Porphyry Bowl, the largest piece of decorative porphyry in England. Formerly of Doughty House in Richmond, the tazza-shaped bowl, is believed to be Roman in origin and repaired in both antiquity and later, before its purchase in the 18th century. The bowl has a diameter of approximately 1.5m.

Pieces were missing from the ancient red Egyptian porphyry bowl, the grey porphyry stem and base of the decorative sculpture. There was also copper staining on the Portland limestone stepped base and some of the exposed Roman clamps had become corroded.

An initial analysis was carried out by the conservation team to investigate the condition, construction and material composition of the bowl. Samples were taken, and plaster casts were created for the areas of loss. The expert team of conservators then removed all the loose pieces and previous adhesive before carefully cleaning them and the correlating sections of the bowl.

A metal detector was used to find the location of the metal fixings, and the cramps which had become corroded were treated to prevent further damage. The conservation team repointed loose pieces of porphyry and fixed them back into position using a polyester resin with powder pigments to tint the resin so that it matched the original character of the porphyry.

To replace the missing areas of stonework, the team needed to source new porphyry and cut it to size using the new plaster masters. Each piece needed further shaping using hand tools and expert craftsmanship whilst being fitted to the bowl to achieve a seamless finish. Two types of porphyry were sourced to restore both the red Egyptian porphyry and the grey porphyry.

All the missing pieces have now been fitted and the bowl has been polished and given a final wax.  The copper staining affecting the base stone has been carefully removed. Trevor Proudfoot, our Managing Director, explains more about the complexity of the project:

“The conservation of the Porphyry Bowl is the culmination of both recent material analysis, and decades of perfecting methods of conserving garden statuary in the care of the National Trust. We have employed craft techniques that copy methods dating from the Roman period as well as the 18th and 19th centuries.”

As part of the project our Norfolk Workshop gave a talk to National Trust volunteers about the history of the Porphyry Bowl and the cleaning methods required to preserve the different fabrics of the sculpture. The overall programme of conservation has not only preserved the bowl for the present but has set up a means of monitoring future decay and will ensure effective repair for many years to come.