What Causes Discoloration in Metals When Using a Butane Torch?

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A new butane torch was acquired, leading to experiments with melting coins. A penny melted easily due to its zinc core, while a dime, composed of a nickel-copper alloy, did not melt despite color changes occurring on its surface. The discoloration, referred to as the hazing effect, is attributed to the metals reacting with oxygen as they heat. The melting points of copper and nickel are significantly higher than that of zinc, explaining the difficulty in melting the dime. The discussion also touches on how heating metals can excite electrons, causing them to emit light in various colors as they return to their ground state.
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i got my new toy today(bought it on ebay sunday). it is a small butane torch.
i melted a penny with it. the coating completely vaporized and the inside(zinc?) melted and such. when i tried to melt a dime, however, it didn't melt. every part of the dime, except where the flame actually touched it, changed colours(multiple times). what causes the discolouration?
 
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I think that disscoloration is called the hazing effect of something like that, when metals heat and change colors. It might have something to do with the metals reacting with the oxygen in the air.

I believe the current composition of a dime is now a 75-25 alloy of nickle and copper. When you make an alloy with different metals, it does some strange things with the metling points, sometimes lowering it, sometimes raising it.
But if you just look at each metals individual melting point,
Copper:1981 F, 1083 C
Nickle: 2651 F, 1455 C
Each one is pretty high, so that might explain why it is so hard to melt.
A pennty however is just copper coated zinc, and zinc's melting point is only 787 degrees F, so it is much easier to melt than a dime.
 
I would also guess that by heating it with an intense flame you are exciting the electrons in the metal causing them to reach a higher state of energy. when the electrons go back to their ground state they emit energy in the form of light (w/ different wavelengths i.e colors).
 

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