Originally Posted by
M1011
Yes this is correct. To simplify, the alloy Rolex uses is the same colour right the way through the metal. Rhodium plated jewellery is not white throughout, it just has a thin white layer on top of the gold which can wear over time to reveal the natural colour beneath.
Yes and no.
You're correct that it'll always be an alloy (pure gold is too soft) and that Rolex uses 18ct on all modern watches.
However, whilst the purity and the size of the watch will remain constant (defined by the design), the weight will differ depending on the alloy used. Using a Palladium mix instead of a Nickel mix will result in a watch that's heavier overall despite having the exact same proportions, as Palladium is denser than Nickel. Therefore you end up with more gold in the 18ct item of the same proportions alloyed with Palladium than with Nickel, as the total item weight will be heavier and the proportion of that weight that is gold will remain constant at 75%.
None of this has any bearing on why watch manufacturers opt for this alloy, but interesting nevertheless.