This photo below is quite experimental and symbolizes the current financial crisis in the Euro zone.
Especially difficult was the light. I mounted my LED torch on a separate tripod to the right of the coin - so that only the burner at the left and the border and backside of the 1 Euro was illuminated but not its glowing front side. Otherwise the red color from the glowing metal would have disappeared.
Difficult was also the short distance of my lens to the fire - my only macro is the the 60mm Nikkor Micro from Nikon. I was glad that the coin was glowing and not my glass.
Last but not least: The span of time until the coin got black from the burner's unburned carbon was relatively short. It took me a pile for 1 Euro coins until I was successful.
Needless to say that I heard this "What have you done with that coins that they are so black?" when I wanted to pay...