Last week I mentioned that I would carry out some tests with a fellow watchmaker to confirm whether or not the rose-coloured plating on vintage Omega watches contained any gold, as a follow up to a discussion that sprouted off of this post on the Omega 321. Following are the results from the samples we tested.
J.Peter made a very good point in stating that the acid used to carry such a test is very strong and, if the plating did contain any gold, it would chew through any impurities very quickly to attack the base metal. To overcome this problem, we took rubbings from the samples in question on a mildly abbrasive, flat, black stone. We chose black because it would allow us to more easily distinguish any traces of gold that may be left from the sample deposits following the acid treatment. The acid we used to carry out the tests was nitric acid, which does not attack gold but quickly dissolves most other metals.
Using old stock parts for the samples we took from watches, we tested four samples from the following sources:
- Oscillating mass of an Omega 565
- Mainplate from an Omega 861
- Mainplate from a generic ETA quartz movement
- One sample of 18K gold
The 18K sample of gold was employed to serve as a reference to which the other samples could be compared. The reason we also chose to test a sample from a generic ETA quartz movement, was to either confirm or dispel the myth that these rather cheap and disposable watch movements are plated in gold. To our surprise, this particular sample led us to believe that they are, in fact, plated in a low karat gold to keep the base metal used in these movements from oxidizing.
Below is an image of the four metal deposits that we tested.
Once the metal deposits had been collected, they were then subjected to nitric acid. The results were rapid and the samples taken from both Omega movements were dissolved almost instantly. Checking under strong magnifaction afterwards yielded no traces of metal left from either Omega sample, while a small amount of the sample taken from the ETA quartz movement remianed unharmed by the acid. The sample of 18K gold showed almost no visual difference prior to and following the acid treatment.
In the end, the myth bust has been confirmed. Vintage Omega movements are not plated in rose gold.
I will continue to hold my stance, however, that Omega’s movements are not plated in pure copper, but rather a form of beryllium-copper, or similar alloy, that keeps the copper content from turning green through oxidization.