Here is a pretty easy question to answer and I am little embarrassed to ask this late in the game. On Proof coins what exactly is cameo? I have always thought of it as the frosted devices sometimes found on proof coins, but now I have had two dealers refer to cameo as the mirrored field portion? Could it just be contrast between the mirrored field and any frosted devices? Let me hear some guidance.
You are correct. You may also see things like "Deep Cameo" or "Ultra Deep Cameo" on slabbed coins. Both of these are equivalent terms and simply mean the contrast is even stronger that would be seen on a "Cameo" coin. Generally, new modern proofs from the US will have the "Ultra Deep/Deep Cameo" appearance.
No need to split hairs. I think of the entire coin as a cameo coin, rather than split the coin into devices and fields. IOW, both you and the dealer are right. If forced to choose just one, I suppose the frosty devices would be the "cameo" portion, not the fields. And it's not just proofs. Proof-like coins are also Cameo and Deep/Ultra Cameo.
No the dealers are not right. Brilliant Proofs have deeply mirrored fields and they are not cameo in any way shape or form. For a coin to be considered cameo or deep cameo you have to have mirrored fields AND frosted devices. A coin cannot be considered cameo if either is missing. The term comes from ages ago, a cameo was a piece of jewelry. It was usually a lady or man's head/bust carved in a white or very light colored piece of material and then set into a darker and very smooth piece of surrounding material. Cameo Jewelry That is where the term comes from. And as you can see, it is the contrast between the devices and background that creates the effect. It is the same thing with coins. The devices will appear white and the background as black if you tilt the coin just so.
Now thats in insightful answer. Doug, Are there many frosted devices on proofs without mirrored fields?
None that I ever saw. But there are plenty of them with the mirrored fields and no frosted devices. Among coins manufactured as brilliant Proofs, cameo and deep cameo examples can be found for virtually all dates, even back to the 1850's. But some are exceedingly uncommon for it wasn't until the early 1970's that the mint made a concerted effort to only issue Proofs that were cameo/deep cameo.