Watch plates are prepared for gilding in the following manner. After being rubbed smooth with water-of-Ayr stone, the plates are immersed for a second or two in a mixture of i parts of hydrochloric acid and 5 parts of nitric acid, both at full strength. They are then thoroughly rinsed and scratch-brushed, after which they are ready for gilding. Sometimes the plates are heated before dipping them in the gold solution: this softens them, but enables a good colour to be got with a very little gold.