| Nitric acid | 200 volumes |
| Sulphuric acid | 100 volumes |
| Sea salt | 1 volume |
| Sulphate of zinc | 1 to 5 volumes |
The duration of immersion in this bath varies from 5 to 20 minutes, according to the dullness required. Wash with plenty of water. The articles will then have an unpleasant appearance, which will disappear on plunging them for a moment into the brightening bath and rinsing quickly.
The pieces are next treated with the nitrate of mercury bath for a few seconds.
| Plain water | 10,000 parts |
| Nitrate of mercury | 10 parts |
| Sulphuric acid | 20 parts |
It is necessary to stir this bath before using it. For large articles the proportion of mercury should be greater. An article badly cleaned will come out in various shades and lacking its metallic brightness. It is better to throw a spent bath away than attempt to strengthen it.
The various pieces, after having passed through these several processes, are then ready for the plating bath.
A few words on the subject of gilding may not be amiss. Small articles are gilded hot, large ones cold. The cold cyanide of gold and potassium bath is composed as follows:
| Distilled water | 10,000 parts |
| Pure cyanide of potassium | 200 parts |
| Pure gold | 100 parts |
The gold, transformed into chloride, is dissolved in 2,000 parts of water and {287} the cyanide in 8,000 parts. The two solutions are then mixed and boiled for half an hour.
The anode must be entirely submerged in the bath, suspended from platinum wires and withdrawn immediately the bath is out of action.