The simplest method of colouring gold jewellery is to bring it to a uniform heat, allow to cool (and thus become annealed), and then boil until bright in a pickle of 8 oz. of rain water and 1 oz. of sulphuric acid. Another method is to anneal the gold, boil it in a pickle of nitric acid and water, again anneal, and dip in the following colouring mixture. Two parts (by weight) of saltpetre and 1 part of table salt are heated in their dry state in a colouring pot or blacklead crucible; when hot, make into a paste with hot water, boil, add 1 1/2 parts of muriatic acid, and stir well- Use at boiling point; leave the gold in the solution for not more than 90 seconds, as the solution removes more or less of the gold. On taking the gold from the colouring solution, rinse it in a pickle, dip it in hot water, and dry in hot sawdust: the gold will be spotted if not thoroughly dried. This method may be used with gold ranging between 12 and 20 carats fine, the best results being obtained with L5-carat gold.

The following pickle has been found very satisfactory for imparting a rich colour to gold rings, scarf-pins, etc. Alum (powdered) 1 oz., common salt l oz., saltpetre 2 oz., and water l0 oz. Wash the article to be coloured in warm water to which a few drops (say fifteen to twenty drops to a breakfast-cup full of water) of ammonia have been added, using a soft brush and soap. Rinse in cold water, and dry in hot sawdust. Then immerse the article in the pickle for about two minutes, and again dry in hot sawdust. Finally polish with rouge.