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TARNISH TEST The tarnish test provides an indication as to whether the metal will discolour in the mouth over an extended period of time. The test requires the cold mounting of two corrosion samples followed by standard metallographic polishing techniques. One of these mounted samples is then fixed into a device which dips the specimen into a freshly made aqueous solution of mol/1 sodium sulfide (analytical grade) at 23 ± 2°C for a period of 10 to 15 seconds every minute. After 72 hours, the test sample is rinsed thoroughly with alcohol and distilled water and then dried before visually examining the surface without magnification. Tarnish is determined by visually comparing the tested and untested samples. |
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