I saw a 640 on the big G auction site that is "etched". Just looks "engraved" to me.

I understand that etching implies a chemical process, but I'd never heard of it on guns before - is that what this is, or is the seller just confusing etching and engraving?

Quite a few people refer to engraving as 'etching'. It's not the same as you point out.
Just a simple mix up in terminology when expressed that way.

Etching these days is typically done with lasers rather than chemicals, and depending on how it is done, can actually produce markings with some depth to them which will not wear off easily.

Still, traditional engraving/stamping tends to look nicer and is obviously more wear resistant.

Typically speaking, laser etching is used as a cost saving measure because it's obviously faster, cheaper, and easier to do than engraving. However, it also doesn't look as nice.

The difference between the two should be obvious at a glance, so if the gun you're looking at appears to be stamped or engraved, then it most likely is and the description identifying it as etching is merely an error.

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Most etching today is laser etched; more precise and less messy than other types, which usually use chemicals and most times is referred to as acid etching.

Acid etching is an old technique, but still does a fine job when the craftsman knows what they're doing. S&W acid etched one commemorative, where most designs were roll stamped or engraved. My NCHP 50th Anniversary M29-2 is acid etched on the side plate. I think it limits what kind of restoration can be done, depending on the finish. This commemorative is nickel plated, not sure if it could be re-plated without affecting the detail of the etching. I don't think it would be an issue on a blued gun.

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