Metal finishing Q&As since 1989

-----

Testing for discolouration of plated parts - Watch Dials especially

2003

Sir,

We are currently conducting "sulfide Test" for our Wrist Watch Dials to check the quality of plating for discolouration. We are using 20% Ammonium sulfide solution along with 1N sulfuric Acid in the ration of 5:1 ( 20ml of Amm. sulfide solution and 5 ml of sulfuric acid). The test is conducted in a desiccator for a period of 6 minutes.

The base material is Brass and the base plating is 3 micron of Nickel. Gold plating of 0.1 micron follows.

I would like to know the following.

1. The chemistry of the reaction
2. Whether this test is appropriate to check discolouration of plating.
3. If not suitable, which other accelerated tests can be conducted for checking discolouration besides UV Test.

Regards,

Suresh. P
- Hosur, Tamilnadu, India

I want to know whether UV TEAST is recommended for the coloured finish of the metal, as per I know it is for the silver finish , to check the discolouration of the silver finish.pl. suggest. if yes what is the chemistry .

Anil Gupta
head prod - Chandigarh, India
April 16, 2008