Letter from Plenderleith to Schaeffer answering his various requests and his technical report on the sectionHarold James Plenderleith

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… but at least no parts were missing. The cup had received a knock in antiquity, doubtless, at the time of fracture; it was somewhat distorted and it was a question whether a satisfactory reconstruction would be possible by reason of this deformity.

In dealing on a course of treatment, experiments were first carried out on laboratory-made niello** and these showed the substance to be remarkably stable in the presence of formic acid, a reagent that dissolves copper compounds while leaving silver and gold unaffected. Before proceeding to the main task, the broken fragments of the bowl were treated individually with formic acid at different strengths and temperatures, and the following procedure which was discovered to be the most satisfactory was applied to the cup itself - immersion for about 20 minutes in a boiling solution composed of 1 volume of commercial formic acid and 2 volumes of distilled water. By this treatment the green incrustation was removed leaving patches of oxydes and reduced copper which were eventually eliminated by local applications of ammonia (.880) and by washing. By such treatment the ornament around the cup was revealed in surprising freshness (Fig. 3)); the niello, for the most part, was in remarkable condition - lime-black, and still preserving its characteristic dull shine in a ground work of silver - and the gold inlays had recovered their rich sheen without any evidence of blanching.

Where corrosion of the underlying metal had opened up the niello, removal of the incrustation caused the gold inlays to become detached, but this was not a serious matter as a complete X-ray record existed showing the position of all the surviving gold inlays and these could be re-set, in due course, in their appropriate positions.

The cup was repaired by making soft solder to join the broken fragments together and unite them to the main place, but narrow gaps created along some of the joints caused by deformation in antiquity. Those were filled with a microcrystalline adhesive ("Amorfix")

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