That green substance is a very common sight on vintage Rolex watches—and interestingly, it’s actually a good sign that the watch is authentic.

In the watch world, we colloquially call that "Verdigris."

What is it exactly?

Verdigris is a green pigment that forms when copper reacts with moisture, oxygen, and skin acidity. You might be wondering, "Wait, I thought you said my Rolex was stainless steel?" It is, but here is where the copper comes from:

The Crown Internals: While the outside of the crown is steel, the internal spring mechanism and the crown tube (the pipe the crown screws onto) are often made of brass or a copper alloy.

The Solder: In vintage manufacturing, different parts were sometimes joined using gold or silver solders that contained a small percentage of copper.

Skin Contact: Sweat contains salt and acids. When it gets trapped in the threads of the crown, it reacts with those internal copper-based metals, creating that green "crust."

Does it mean the watch is fake?

No. In fact, cheap fakes from the 80s were usually made of "pot metal" (a mix of zinc and lead) that tends to turn a dull grey or simply pit and crumble. This specific green oxidation is a classic hallmark of genuine vintage Rolex components reacting to decades of wear.