Metal Finishing Guide Book

2012-2013

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Table III. A Selection of Typical Acid Gold Color Baths for Thick Deposits Hamilton 22k Yellow 24k Yellow 1N 2N 3N Gold (g/L) 4-8 4-8 4-8 4-8 4-8 Conducting salts (g/L) 120 120 120 120 120 Nickel as nickel metal (g/L) 0.2 ��� 7-10 4-6 1-3 Cobalt as cobalt metal (g/L) 1 0.5 ��� ��� ��� pH 4.0-4.5 4.4-4.8 4.0-4.2 4.0-4.2 4.0-4.2 Temperature (��F) 90-100 80-90 120-140 100-120 90-100 Current density (A/ft2) 10-20 10-20 10-20 10-20 10-20 Required Required Required Required Required Agitation 5. Temperature. The effect is similar to current density. Low temperatures favor the gold yellows, and higher temperatures favor the alloy colors. Temperatures over 160OF should be avoided, except in the case of rose golds, because of the rapid breakdown of cyanide and the darkening of the color. 6. pH. It is rarely necessary to adjust the pH of a gold or gold alloy bath. They are usually buffered between pH 10 and 11. Only pink, rose, or red golds are favored by higher readings. BARREL PLATING (CLASSES A AND B) Gold as KAu(CN2), 0.4 g/L Free cyanide as NaCN, 30 g/L Disodium phosphate, 23 g/L Temperature, 100-120��F Anodes, stainless steel (1:1 or better) In typical jewelry barrel plating about 6 V is necessary. A decorative finish of 0.000002 in. is deposited in 3 to 4 min. If the parts are small and densely packed in the barrel it may be necessary to plate up to 8 min to get even coverage. The above formulation may be altered to achieve various colors. Champagne or light Hamilton colors may be achieved by adding 1.5 to 3 g/L of nickel. Lowering the temperature will also produce a lighter and more uniform color. ANTIQUE GOLDS (CLASSES A AND B) The art of the 19th-century platers was to produce a finish that looked as if it had been mercury gilt over silver or copper (vermeil) and buried or weathered by the elements for a century or so. Each master plater developed an antique finish that was his trademark. The basic modern method to achieve this effect is as follows: Table IV. Industrial/Electronic Gold Plating Plating Method Purity Knoop Hardness No. Surface Rack Barrel Continuous 99.95% 60-80 Matte Yes Yes Yes Printed/etched circuits 99.5-99.7% 120-180 Bright Yes No Yes Contacts/connectors 99.5-99.7% 120-180 Bright Yes Yes Yes Semiconductors 330

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