Metal Finishing Guide Book

2011-2012 Surface Finishing Guidebook

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tin, has a pewterlike finish. This alloy is known as speculum. A typical formulation is as follows: Sodium cyanide Copper cyanide Sodium stannate Sodium hydroxide Rochelle salts Temperature 5 oz/gal (37 g/L) 2.7 oz/gal (20 g/L) 7.5 oz/gal (100 g/L) 11.5 oz/gal (10 g/L) 5 oz/gal (38 g/L) 160° F (70° C) Operation of this solution is very similar to the standard bronze solution. Control of the alloy depends on analysis of the deposit since the color does not vary with minor changes in analysis. Fairly frequent addition of stannate salts is necessary due to the large tin content of the deposit. 176

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