Patent ID: 7481872

Claim:
A process for making a bath composition, comprising the steps of: (a) dissolving the following in water (i) aluminum sulfate at a concentration of about 10 to about 30 grams per liter of solution, (ii) oxalic acid at a molar ratio of oxalic acid to aluminum sulfate in the range of about 1.5 to about 4, (iii) nitrobenzenesulfonic acid at a concentration of about 2 to about 4 grams per liter of solution; (b) adjusting the pH into the range of about 3 to about 5 by adding sodium hydroxide after the aluminum sulfate, oxalic acid, and nitrobenzenesulfonic acid are fully dissociated in the water; and (c) adding ferrous sulfate at a concentration of about 0.1 to about 0.5 grams per liter of solution.