I picked up this Vespasian denarius for like $12 or something. I tend not to go for silver too much, but it was cheap so why not. I got it and i noticed it has some interesting shiny blue toning on the edges of the coin. The coin may be been overheated at some point - would this heat or flame cause the blue color?
My guess is that the coin was stored in a paper envelope for a long period. If the envelope was manila, as most were many years ago, the sulfur in the paper could cause the silver to tone blue and yellow/gold. That's a nice buy at $12!
Sulfur tends to do that. Earlier, I tried to repatinate a super shiny silver coin with elemental sulphur. I heated it in the oven, then forgot about it, only to find a 200 C completely black coin with molten sulphur attached. After some cleaning (the coin did not turn out nice), some similar blueish patina remained as on your coin. Do not bake your coins.
Yes, silver is extremely reactive to sulfur. Exposure to it can turn it black very quickly, especially if the coin is heated in the oven. Controlling the process is key. Liver of sulfur will darken metals, except gold. This is especially true for silver, copper and bronze. Using the correct concentration is very important. Generally speaking, it is best to use a more diluted concentration to have more control with the process. If any heating is done, it is to the "bath" and not the coin or object. The purpose of the heating is to achieve better dissolving of the sulfur in the water, which should be distilled water. The coin or object should be room temperature. Heating it with the sulfur solution on it will create an undesirable black (unless that's the objective). I recently got a nice Philip II coin of Naples. Unfortunately it was cleaned to the point of being extremely shiny. I applied a very diluted sulfur solution to it for only a minute at the most. This process darkened the coin somewhat, but the fact is the cleaning remains. However, given time, the coin will assume a somewhat more attractive appearance, although the label includes the notation "harshly cleaned".
