This is one of the seven Anglo-Saxon disc brooches found within a silver vessel discovered by a metal detectorist in September 2014 – one of more than 100 objects that were subsequently excavated and are now known as the Galloway Hoard (see CA 297 and CA 376). Made of silver and copper-alloy, the brooch – thought to have been buried c.AD 900 – was heavily corroded on discovery, and needed to undergo a careful conservation programme, carried out by Bethan Bryan, Assistant Artefact Conservator for National Museums Scotland.
The brooch was first recorded in minute detail, which included taking X-rays and photomicrographs of the surface. Once recorded, cleaning tests on other samples of silver and copper-alloy were carried out to determine the best methods to employ. These tests found that using a scalpel manually under a microscope was the most successful way of removing the corrosion from the back plate. In this way, everything could be carefully controlled, which would have been impossible using chemical methods. In areas where the corrosion had caused significant thinning of the plate, the acrylic polymer Paraloid B72 was used to consolidate it.
The scalpel could not be used on some areas on the front of the brooch, however, where the decoration was too intricate and the thin layer of gold too delicate. A porcupine quill was found to be a great substitute, able to get into the tight corners of the vine-scroll decoration without doing any damage. Once as much of the corrosion as possible had been removed, the whole brooch was consolidated using a protective layer of a stronger acrylic polymer, Paraloid B48N.
Find out more about the Galloway Hoard at https://nms.ac.uk/gallowayhoard.
Text: K Krakowka / Images: National Museums Scotland