The question of copper and silver sticking to each other (bonding or adhesive was the question?) came up in that other thread but I'm starting a new one here for it. This denarius of Domitian Caesar is not a fourree. The copper you see is on top of the silver not the other way around. Making a photo that makes this clear is a real problem but a stereomicroscope allows the diagnosis with ease. My best guess is that the coin was hoarded with copper coins and they once were corroded together into a solid block. This was probably separated chemically dissolving away the very corroded copper coins leaving some copper tightly adhered/bonded to the silver. This coin survived harsh cleaning pretty well probably because the silver used for it was relatively pure. I do wonder if the attachment is if fact aided by a naturally formed eutechtic (72/28) bond between the two. I suppose that would require cutting the coin to see a cross section so we won't know. I bought this coin as a solid coin from a dealer who actually knew the difference or was so blind that he didn't notice the situation. This was in 1989 and I doubt I'll ever know. A collection of plated coins needs one of these.
Not seen this before, I would have disregarded this if I hadn't been looking for a fouree. Learned something else.
I don't think that eutectic bonding would be the reason. The temperature for the 72/28 Au-Ge is above 360 degrees C. I also couldn't find any bonding info on Cu-Ag in such a reaction. Cu, Ag, and Au use metallic bonding for reactions, and since they delocalize the outer electrons ( S and P ) to make a "sea" of electrons around inner nuclei, Quantum theory gives them interesting bonding ability with each other.
i'll be darned, that's interesting. would have never have guessed that's what it was from the pic. I do have some Chinese cash coins I've separated where some of one coin is fused to anther...but both are AE.
Nice denarius, Doug! Looking closely at the photo I can believe that the copper is actually above the surface, but without any explanation I would probably believe it was plated as well. The following victoriatus has something similar going on on the surface, particularly on the reverse. I purchased it in this state from an eBay seller who apparently tried to clean it but was not able ot make any further progress. It's currently in the hands of an expert coin cleaner I know. He said the surface has a layer of some sort of copper or zinc compound that is requiring a combination of chemical and mechanical cleaning to clean. It's unfortunately still not done but I will be sure to share an "after" picture when it's finished.
I find this a bit hard to follow also......Are you saying the melting points are not reachable for bonding so some other process is involved??? Quantum mechanics??
