Doctoring
American Watchmaker and Jeweler (1892)
Important: Safety Warning
This page describes trade processes that use dangerously toxic materials such as cyanide solutions, mercury amalgams, or strong acids. These processes require training, equipment, and precautions far beyond what the text describes.
This information has been left in for historical purposes but should not be acted upon.
This term is applied to plating defective places which occurred either by accident or negligence on the part of the operator. It is equally applicable to gold, silver or nickel plated articles. Take a piece of the anode, be it gold, silver or nickel, about the size of your little finger and connect it with the positive pole by a thin copper wire. Around this anode wrap a piece of ordinary muslin several times; hold the defective article on the top of the positive pole, and after dipping the anode in the solution until the muslin is thoroughly soaked, move it to and fro over the defective place, and a coating is thus formed. Recovery of Gold from Bath. To recover gold from bath evaporate the bath to dryness, mix the residue with litharge and fuse the mixture. A lead button is thus formed in which all the gold is contained. Dissolve the button in nitric acid, and the gold will remain behind in the form of small flakes. Filter off and dissolve the flakes in aqua regia. Recovering Gold from Coloring Bath. Dissolve a handful of sulphate of iron in boiling water, and add to it your "color" water; it precipites the small particles of gold. Now draw off the water, being very careful not to disturb the auriferous sediment at the bottom. You will now proceed to wash the sediment from all traces of acid with plenty of boiling water; it will require three or four separate washings, with sufficient time between each to allow the water to cool and the sediment to settle, before passing off the water. Then dry in an iron vessel by the fire and finally fuse in a covered crucible, with a flux. Recovery of Silver from a Bath. To recover silver from cyanide bath; evaporate the bath to dryness, mix the residue with a small quantity of calcined soda and potassium cyanide and fuse in a crucible, and the metal will be found in the form of a button in the bottom of the crucible.
What Has Changed in the Last Century
The technique the American Watchmaker and Jeweler described in 1892 — wrapping muslin round a small anode, soaking it in solution and rubbing it over a bare patch — is still in everyday use, now under the name brush plating or selective electroplating, with purpose-made swab tools, rectifiers and pre-packaged solutions instead of a wire and a scrap of cloth. What has changed is the chemistry and the law: cyanide baths of the kind casually handled here are now tightly controlled workplace hazards in most countries, and non-cyanide gold and silver formulations are common, while nickel is a recognised skin sensitiser and is restricted in items meant to touch the skin. The recovery methods — cementing gold out with iron sulphate, fusing residues with litharge, dissolving the lead button in nitric acid — are recognisable assay-office chemistry, but scrap and spent baths now normally go to a licensed refiner rather than being boiled down at the bench. The instructions read as sound trade practice for their date; only the safety and disposal assumptions have moved.
Written for this edition, 2026.