Touchstone for gold assay

Description

The cost of gold constantly gave occasion for forgery or misstatement of the gold content of gold products. The scraping test is an old and simple method of testing gold content, and is used by goldsmiths even now. The gold to be tested is rubbed on a black slate touchstone so as to leave a mark. The colour of the mark is compared to that of needles of precisely known gold content. The assay with acid is somewhat more exact. The mark on the touchstone is dabbed with several acids calibrated against the usual gold alloys. The acid that dissolves the mark indicates the fineness of the gold alloy. For very exact measurements the fire test (which cannot here be described in detail) is used. It has, however, the major drawback that a sample must be cut out of the object, involving a considerable intrusion. The touchstone shown here is a particularly finely made goldsmith's instrument from the mid C16. The gilt brass ferrule fitted to one end of the touchstone has two unidentified escutcheons on its narrow sides. On the wide sides floral ornament and the date 1546 are engraved. The narrow sides of the stone have relief decoration.