After spending over 1,000 years within the soils of Galloway, it’s no marvel objects from the Galloway Hoard wanted some critical work earlier than happening show. Bethan Bryan talks by the complicated strategy of conserving a silver brooch, from mending “mini-volcanoes” of copper erosion to utilizing porcupine quills and algae-derived gels.
It has been a delight and privilege to preserve one of many brooches from the Galloway Hoard. My background is in early medieval archaeology, and so it was a dream come true to be provided the prospect to work on such a stupendous and traditionally necessary object. The work concerned detailed scientific examination and evaluation of the corrosion and supplies of the brooch, after which conservation of the brooch itself.
The Galloway Hoard, found in September 2014 by a steel detectorist, accommodates over 100 objects together with silver jewelry and huge portions of silver ingots. Lots of the hoard’s objects, together with a number of silver brooches, have been contained inside a silver gilt vessel buried originally of the tenth century. Clearly, silver makes up a substantial a part of the Galloway Hoard’s story.
The thing I labored on was a silver and copper-alloy composite disc brooch. It’s the smaller of a pair of very related brooches throughout the hoard, which general contained 5 Anglo-Saxon disc brooches of a form not discovered earlier than in Scotland. An identical brooch was discovered within the Pentney Hoard from Norfolk, England.
The entrance of the brooch is a disc of silver with pierced or/lower open-work vine ornament and a central, equal-armed cross. The gilded entrance floor of the copper-alloy again of the disc may be seen by the lower. The entrance of the brooch is adorned with 4 open-mouthed beasts’ heads, every adorned with niello inserts. Niello is a black metallic alloy of sulphur, often alloyed with silver or copper. It’s used to fill designs which were lower into the silver floor. There are additionally 5 silver, spherical bosses. The silver and copper-alloy discs are riveted along with silver pins. On the again of the brooch is a spring-hinged pin and catch plate additionally riveted on to the copper-alloy disc.
The adorned entrance has been lower by hand. Imperfections can enable us to really feel a human reference to the maker; software lower marks are seen in locations on the silver, and the vines are irregular in form and dimension. The 4 beasts’ heads have additionally been adorned individually, every bearing its personal distinctive sample of niello-inlay.
Earlier than any conservation work may start, the brooch was absolutely assessed, recorded and photographed. This included taking X-rays and photomicrographs to report the floor intimately, small samples of the corrosion merchandise, and evaluation underneath the Scanning Electron Microscope.
As soon as the brooch was absolutely recorded, it was time to preserve it. The again of the brooch was closely corroded across the edges. Cleansing exams have been carried out on samples of copper alloys and silver by Dr Mary Davis, the lead conservator for the Galloway Hoard mission, to evaluate their potential impact on the brooch.
It was determined from these exams that the easiest way to take away the corrosion from the copper-alloy back-plate of the brooch was to take action manually with a scalpel, underneath a microscope. This fashion the corrosion elimination may very well be fastidiously managed, and no chemical compounds would probably change the underlying floor situation and color of the copper-alloy.
The copper-alloy back-plate was very skinny and delicate in lots of locations, particularly across the edges. Some areas needed to be consolidated with Paraloid B72 to present them sufficient power to forestall lack of materials in the course of the conservation course of. Paraloid B72 is an acrylic polymer and is used quite a bit in conservation as each an adhesive and a consolidant. In some locations it was found that the back-plate had corroded by fully, and so elimination of the corrosion revealed small holes. The sides of those holes have been additionally consolidated with Paraloid B72.
There was a lot much less corrosion on the entrance of the brooch, and the silver was in a greater and extra steady situation than the copper-alloy of the again plate. The corrosion on the gilt floor of the entrance of the back-plate was eliminated with a porcupine quill tip, underneath a microscope. The porcupine quill was robust sufficient to manually take away the copper corrosion spots, however tender sufficient to not scratch the tender and skinny layer of gold.
The softer areas of inexperienced copper corrosion on the entrance silver disc of the brooch have been additionally eliminated manually with a scalpel, underneath a microscope. The more durable corrosion spots on the silver have been first softened with an agarose gel, after which eliminated with the scalpel.
Agarose gel is constituted of agar and is non-toxic and eco-friendly. Agar is derived from sure sorts of algae and is a kind of carbohydrate (for instance, starch or cellulose) known as a polysaccharide. It’s soluble in scorching water, can be utilized to type a gel and is steady in each alkaline and acidic situations. The gel acts as a molecular sponge and solubilises impurities, drawing them away from the floor, after which holds the impurities throughout the gel matrix. The gel I used included within the combine alkaline Rochelle answer (a mixture of sodium hydroxide, potassium sodium tartrate and water). This answer has been used on the British Museum for the previous 50 years for cleansing debased silver cash (silver which has a big copper content material).
In some elements, you’ll be able to see the place the copper-alloy back-plate has utterly corroded, even creating small holes by the gold layer on the entrance the place the corrosion merchandise have pressured their manner by. Many copper corrosion merchandise take up extra room than simply pure copper steel or the copper-alloys utilized in metalwork; they’re extra voluminous. The results of that is what I wish to name ‘mini-volcanoes’ of copper corrosion bursting by the gold layer.
As soon as the corrosion merchandise have been faraway from each the silver disc and the gilt surfaces, I consolidated the gold entrance of the copper-alloy back-plate this time with Paraloid B48N. That is stronger than Paraloid B72. I used this to supply further power to the gold on the corroded copper-alloy disc and the entrance of the disc itself. Doing this, would hopefully enable for additional elimination of corrosion from the again of the brooch.
As soon as the gilt entrance of the copper-alloy disc had been consolidated, extra of the voluminous copper corrosion may very well be eliminated safely from the again to disclose the unique surfaces. This was a time-consuming and delicate job with a scalpel and dental instruments, because the copper-alloy disc was nonetheless very fragile.
As soon as the corrosion had been eliminated to an appropriate stage and the conservation course of was full on the brooch, I consolidated the entire of the brooch with a protecting layer of B48N. This acts as a consolidant, lacquer and moisture barrier to guard the brooch. The brooch was now prepared for show.
