Stronger: A boiling solution of potassium chlorate, 25 parts, in water, 250 parts, poured into a mixture of pure hydrochloric acid, 250 parts; water, 400 parts.
Very strong: A boiling solution of potassium chlorate, 30 parts, in water, 300 parts, poured into a mixture of pure hydrochloric acid, 300 parts; water, 300 parts.
For etching on copper a saturated solution of bromine in dilute hydrochloric acid may also be used; or a mixture of potassium bichromate, 1/2 part; water, 1 part; crude nitric acid, 3 parts.
The following are also much used for copper and copper alloys:
I.—A copper chloride solution acidified with hydrochloric acid.
II.—Copper nitrate dissolved in water.
III.—A ferric chloride solution of 30° to 45° Bé. If chrome gelatin or chrome albumen is used for the etching-ground, a spirituous ferric chloride solution is employed. The etching process can be made slower by adding common salt to the ferric chloride solution.