this exposed them to the risk of being copied by competitors. Boulton wrote in 1771, "I am very desirous of becoming a great silversmith, yet I am determined not to take up that branch in the large way I intended, unless powers can be obtained to have a marking hall [assay office] at Birmingham." Boulton petitioned Parliament for the establishment of an assay office in Birmingham. Though the petition was bitterly opposed by London goldsmiths, he was successful in getting Parliament to pass an act establishing assay offices in Birmingham and Sheffield, whose silversmiths had faced similar difficulties in transporting their wares. The silver business proved not to be profitable due to the opportunity cost of keeping a large amount of capital tied up in the inventory of silver. The firm continued to make large quantities of Sheffield plate, but Boulton delegated responsibility for this enterprise to trusted subordinates, involving himself little in it. As part of Boulton's efforts to market to the wealthy, he started to sell vases decorated with ormolu, previously a French speciality. Ormolu was milled gold (from the French or moulu) amalgamated with mercury, and applied to the item, which was then heated to drive off the mercury, leaving the gold decoration. In the late 1760s and early 1770s there was a fashion among the wealthy for decorated vases, and he sought to cater to this craze. He initially ordered ceramic vases from his friend and fellow Lunar Society member Josiah Wedgwood, but ceramic proved unable to bear the weight of the decorations and Boulton chose marble and other decorative stone as the material for his vases. Boulton copied vase designs from classical Greek works and borrowed works of art from collectors, merchants, and sculptors. Fothergill and others searched Europe for designs for these creations. In March 1770 Boulton visited the Royal Family and sold several vases to Queen Charlotte, George III's wife. He ran annual sales at Christie's in 1771 and 1772. The Christie's exhibition succeeded in publicising Boulton and his products, which were highly praised, but the sales were not financially successful with many works left unsold or sold below cost. When the craze for vases ended in the early 1770s, the partnership was left with a large stock on its hands, and disposed of much of it in a single massive sale to Catherine the Great of Russia—the Empress described the vases as