It's hard to pick a favorite thing that you love about toning in a series; but for me, it has to be when you see this sort of "lava flow of color" into the recesses of a coin design. I am not 100% sure why this effect happens. I bet someone on this board might know the physics of this. It almost looks like the color melted and flowed into the low spots, like molten rock or some sort of colorful liquid element flowing like a river through the valleys. This is just beyond beautiful. I am not sure if this type of toning happens in other series, it probably does, but I seem to see it most of the time in the Morgan Silver Dollar series. Example #1: Pink molten lava flows around cool green mountains ... (PCGS MS63 OGH) Example #2: Cool turquoise blue water laps against the brown, gold, and green hillsides ... (PCGS MS64)
Beautiful! It all has to do with the thickness of the silver sulfide layer. It doens't "flow", it just deposits at a different rate.
Thanx for the link. Until I have it, FMI how does a black compound like silver sulphide reflect light in spectrum of colour? Is toning a not a combination of silver insoluble compounds including halides, nitrates and sulphide in combination with insoluble copper related compounds like copper chloride and carbonate (verdigris platina)? I mean, "coin chemstry", if you may call it that, does not supercede the broader field of metallurgy.
Yea, yea....LOL I wrote the book while I was laid off. These days I'm working my edited off. The time will eventually come to finish it up.
As I recall the reason for the coloration (which is dependent on the thickness of the silver sulfide layer) is called thin film interference. Here is a brief overview of the physics: http://www.physicsclassroom.com/class/light/u12l1c.cfm It is only after the silver sulfide layer exceeds a certain thickness that it becomes black.
Looks like a good read. It appears there is a 2004 and 2006 version, and just found a 3rd edition, 2010 here http://www.collectons.com/shop/item/58459/Coin-Chemistry-Book-3rd-Edition-by-Weimar-White Looking forward to reading it - thanks for the suggestion BadThad
