The granular or matted finish given to the surface of brass clock parts prior to gilding. It is produced by dipping the parts briefly into a concentrated mixture of nitric and hydrochloric acid, after which they are rinsed and brushed in a circular direction with a scratch brush. A 'grey' surface on steel or brass is produced by rubbing the parts on the surface of a glass plate smeared with a paste of oilstone dust and oil.