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How To Recognize Corrosion in Vintage Rolex Watches

The stainless steel used in vintage Rolex watches is an alloy recipe made from Iron Ore, Chromium, Nickel, Molybdenum and a few other trace elements. Its these trace elements that give the iron ore its stainless, corrosion-resisting properties.

Metallurgists call this alloy 300 Series Austentic Stainless Steel. 316 is considered standard marine grade stainless steel, but despite the name is not resistant to warm seawater corrosion (specifically, Chloride, Fluoride, Iodide and Bromide).

304L and 316L (316L being the low carbon version of 316) is derived from this 300 Series and is used in many pre-1987 Rolex Oyster cases. Later Oyster cases use 904L steel with subtly different properties.

The common misconception is that 904L was adopted for its “hardness” and better scratch resistance. The fact is, 316L has a higher Rockwell Hardness Rating (HR B 95) than 904L (HR B 70–90) and 316L is harder, more scratch resistant and tougher to mill than 904L. It’s said to hold a better polish too. 904L does however have better salt and acid resistance.

Urine attacks all austentic stainless steel, so don’t pee on your watches(!) and rinse well after swimming. Bromide is just as bad so keep your watches out of the hot-tub and away from the salt water spa.

Image Source: Google Image Search. Oyster case back pitting

Rolex selected 904L as a solution to the pitting and crevice corrosion it observed on the Oyster mid cases of its sport and tool watches.

It’s said that stainless steel needs to breath and that regular cleaning with fresh water is necessary.

When two pieces of stainless steel touch one another (such as a case back and mid case) cleaning and breathing is inhibited and despite the trace elements, corrosion will occur. Waterproof gaskets can accelerate this by trapping and retaining salts and oxidants which with time will almost certainly trigger a galvanic reaction.

Image Source: Google Image Search

Like seawater, human sweat is highly acidic and rich in halides. Osmosis and capillary action will draw these corrosive elements into the case. With repeated exposure and evaporation the concentration of halides and oxidants accumulate and concentrate, giving rise to a reaction that compromises and penetrates the stainless protection offered by the trace elements.

Image Source: via Google Image Search

This is a chain reaction that once started is almost impossible to halt. It is observable as pitting and once started it can not be stopped, short of grinding out the pit and filling with laser welding. Even this drastic intervention is controversial as it may not entirely halt the corrosion and may only serve to weaken the geometric lattice structure of the surrounding steel (through heat expansion and cooling contraction).

Pitting is bad news and will shorten the life and destroy the value of a vintage watch. It is a slow and progressive chronic condition and while some collectors enjoy the Wabi-Sabi aesthetic others consider it a cancer.

While it shouldn’t prevent you from enjoying the life left in a beautiful vintage watch, you should know that it will negatively affect longevity, collectability and value.

This and much, much more is discussed in the book, The Vintage Rolex Field Guide. To learn about offers, give-aways and opportunities, join our mailing list.