Plexi vs. Crystal?

Here is a photo of Rolex Submariner 16610 that was dropped on a tiled floor. Due to the impact, the crystal glass cracked. Number of small glass particles went through date display window and found their way into the movement.

One not-so-small bit was lodged between sweep seconds wheel and centre wheel bridge which caused the watch to stop.

The owner was lucky that apart from a bent escape wheel pivot, no other damage was found. To my surprise, the balance wheel and escape wheel shock absorbers were not 'activated'.

Conclusion: If you crack the crystal, complete overhaul is MUST - even if you have a brand new watch or one that has been recently overhauled. For that reason watch fitted with plexyglass would be more useful under tough conditions (military or sport activity).

[Q]: Can I trouble you to explain or point me to some info on how the shock absorbers are supposed to activate?

In electrical circuit, the circuit breaker's job is to cut off the circuit whenever the current jumps above a safe level.
In mechanical watches, an equivalent of circuit breaker is shock protection system. The shock protection system is there to protect the critical alignment of components in the event of an unexpected physical shock, such as being dropped.
The pivots and jewels of the balance wheel are fragile in comparison to the mass they need to support, and without shock protection are the most likely part of the watch to be damaged under impact.

The Incabloc (or Kif in Rolex) system uses a specially shaped spring to allow the delicate jewels and pivots to shift in their settings under impact . When the impact is over, the springs guide the parts back to their original positions. If the impact is excessive, the shock protection system is activated and it needs to be reset by watch repairer.
Unfortunately shock protecting system is not perfect and it's efficiency and ability to protect vital parts is not always all that great. Angle of impact, G-force and surface play their role. In some cases, a relatively small drop could cause major damage and in other substantial drops cause very little or no visible damage.

[Q]: What is the difference between plexi glass, mineral glass and sapphire crystal?

Plexiglass is a clear, lightweight type of plastic. Mineral glass is ordinarily glass hardened by a tempering process. Synthetic sapphire crystal is a very hard, transparent glass made of crystallizing aluminium oxide at very high temperatures. When it is heated, the synthetic sapphire forms round masses that are sliced into pieces with diamond-coated saws. These disks are then ground and polished into watch crystals.

Plexiglass, as one would expect, is the least expensive. It is also the least likely to shatter and the most likely to become scratched. Mineral glass, even though it has been hardened by a tempering process, is more likely to break than plexiglass. But it is also more scratch-resistant than plastic plexy. Synthetic sapphire is the most expensive glass crystal and the most scratch resistant. Watch crystals made of synthetic sapphire are often marketed as "scratch resistant", meaning they are very difficult - but not impossible - to scratch. Diamond can scratch them; so can man-made materials that incorporate silicon carbide. As pointed out by other forum members, due to the hardness of sapphire crystal, it is also brittle and shatters more easily than mineral glass or plexiglass.

Unlike plexy, mineral and sapphire crystals can not be re-polished.

Which crystal is fitted to your Rolex watch? An easy way to tell this is by model reference number: in general, watches with 4 code reference number (like 5513, 1680 etc) are fitted with plexy and 5 digits (16233, 16610 etc) are fitted with sapphire crystal.

"Brand new in a box"

This Rolex just came in today. An "E" serial NOS ca. 1991, apparently new old stock, unworn watch. Note the absence of any wear under the lug (yellow arrow). Even internally, the watch looks as good as brand new however this could fool only a novice watch collector.



The auto rotor assembly reveals a different story- the watch is long time overdue for complete overhaul. Note the 'saw dust' all over the rotor bridge: this mixture of dirt, gummed-up oil and metal particles would kill the watch in just few months.



Beware of NOS ! All NOS do need complete overhaul before they could be worn again. Buying an expensive timepiece from a fellow collector could be problematic, even when the seller is completely honest. "Never worn" or "worn only on special occasion" usually means overdue for an overhaul! If you really like the watch then offer the seller to split costs of having it overhauled.

[Q]: What is the difference between BNIB and NOS?

BNIB (Brand new in box) and NOS (new old stock) are commonly abused terms in watch trading. In my books, BNIB means only one thing: a brand new in box, purchased directly from dealer, where the definition of a dealer is "person who sells watches for a living". The very moment you leave dealer's shop, it is no longer BNIB.

If you are buying something from someone who is not a dealer then you are not buying BNIB. At the best it is LBNIB (like brand new in box) and you are not necessarily the second or third owner either. NOS apply to OLD / VINTAGE unsold watches that are no longer in production. Unfortunately, this means different thing to different people.

In this particular case, the watch was possibly wound manually or was sitting on watch winder, or worn on a different bracelet or leather strap. Maybe just for a day or two. The point is this: it EXTERNALLY looks like NOS yet internally something has happened in the past to cause the wear as shown on photo.

Rostfrei Rolex ?

A heavily corroded and pitted Rolex steel case, as demonstrated in the area under the case back seal. Ref 16233, E serial. Fairly common with watches that are 20+ years old. This particular watch has never been exposed to salt water, and has been worn only occasionally as a dress timepiece.