For some strange reason I have always thought that Rolex 16613 winding crown is made out of solid 18K gold.

You too? Really? Small world...

Well have a closer look then. The guinea pig is Rolex crown removed from 16613 Sub (W serial).

... and here is the close-up:

Very strange indeed. The crown is actually not a solid piece at all!

It is actually a 'gold cap' over some other metal...

... which does not really look like gold at all :-( The top layer weighs just over 0.2 gram.

So what is the base metal? Maybe just a lower carat gold? Let's test it !

Small amount of metal dust from gold cap and crown body is taken as sample. Plus an amount of brass as control material - from a brass clock key :-)

To test the metal for it's gold content apply a drop of 'carat' test acid and watch for the chemical reaction. If the metal dust is 'eaten away' then it does not contain gold.

In our case the top 'cap' layer is 18K gold. Unfortunately for goold lovers the rest of the crown is not made out of gold at all.

Conclusion: since the total weight of base metal and 18K gold cap is 0.672 gram, the amount of pure 18k gold in Rolex Sub crown is approximately 33.6 %.

But is this good or bad news?
Good news indeed!

If the crown was made entirely of solid gold, then the locking tread would be way too soft - which could possibly compromise water resistance of your Submariner.

Update: here is the comment received from a Rolex serviceman:
In the production of the cases, bezels and bracelets (wheather full gold or TT, solid or hollow links) it IS SOLID GOLD, no plating, bonding etc.... All gold models tubes are also made of gold. The only time when gold is bonded in any way shape or form is on the clasps of TT watches and in the past in the production of winding crowns... As has been shown already the winding crowns of watches produced before approximately 2 to 3 years ago were "capped" with a thick gold cap. Models produced after this time are fitted with "monobloc" crowns. As the name suggests, these are made of solid single blocks of gold, NOT capped."

In order to confirm above statement, I have examined the latest model crown .

Crown removed from of Y5 serial 16613.

The new crown (monobloc) certainly looks different than the old one. However, in this case monobloc is fancy name for something that is .... hmmm.. how to put it...HOLLOW. Although the crown is made of solid 18K gold, it is really very lightweight.

I would hate to rip this one apart, but it is obvious that the gold mass is still under 1 gram. Hardly a MONOBLOCK to me.

Feel free to email your comments.