Brooch – Scottish Pebble Jewel
An antique silver-coloured Scottish ‘pebble’ brooch¹ principally set with a rub-over round citrine and a radiating spray of jasper agates of various compositions and appearance set within a knurled ornamented edging. Secured with a pin and hook clasp. Circa 1860-1870.
Details of the Setting.
Measuring: 33.75mm x 32.60mm.
Unhallmarked and no stamps observed: tested and valued as sterling silver.
Assessment of the Gemstones.
Cut: round eight-main brilliant-cut crown over two-tiered step-cut pavilion.
Measuring: 9.11mm (depth immeasurable – closed back setting).
Estimated weight: 2.98cts.
Colour: deep orange yellow (7.5Y.14/6).
Species: two ‘bloodstones’ (heliotrope), two red jaspers, one grey banded agate and one brown banded agate (all microcrystalline quartzes²).
¹. They were a speciality of the Edinburgh workshop. The silhouette of the jewel was cut out in thin metal. This space, or background was repeated in thicker metal with holes fretted out to admit the stones. The two were then hard soldered together, one on top of the other. The stones - jasper from Ayr, bloodstone from Perth, Pentland pebble from Arthur’s Seat, jasper from Midlothian - were sliced up on a rotating disc charged with oil and diamond dust. They were then nipped roughly into shape with pincers. For ease of handling each stone was cemented to the top of a stick and ground to shape on a lead disk smeared with emery and water. The stones, still unpolished, and set in the mount with shellac. The rough face was then ground flat and polished on a lead disc with ‘rottenstone’ (a decomposed siliceous limestone, used a power or paste for polishing) and water. The brown or yellow cairngorm that so often occupies the centre of these jewels were set last of all (Peter Hinks, ‘Victorian Jewellery', 1991).
². Microcrystalline varieties of quartz are divided into two types depending on their structure: fibrous and granular.
Chalcedony is the general term applied to fibrous varieties. It is generally a brown to grey, translucent variety, with waxy lustre, often mammillary and in other imitative shapes. Chalcedony has been deposited from aqueous solutions and is frequently found lining of filling cavities in rocks. Colour and banding give rise to various varieties.
Agate is a variety with alternating layers of chalcedony having different colours and porosity. The colours are usually in delicate, fine parallel bands. The bands are commonly curved, in some specimens concentric. Some gates have the different colours not arranged in bands but irregularly distributed.
Heliotrope or bloodstone is a green chalcedony with small amounts of red spots of jasper in it.
Jasper is a granular microcrystalline variety of quartz usually coloured red by included haematite.
Microcrystalline quart is a common and abundant mineral occurring in a wide variety of geological environments. It is present in many igneous and metamorphic rocks and is a major constituent of granite pegmatites. It is the most common gangue mineral in hydrothermal and metal bearing veins and in many veins is essentially the only mineral present (Cornelis Klein and Barbara Dutrow, ‘Mineral Science’, 23rd Edition, 2007).