Some myths and misunderstanding about toning

Well, it's been a while since I've done anything with this post so I decided to add a little more here...



Above is a pic of a star on a naturally toned Morgan Dollar. It shows the common shadow effect due to the atomic restructuring of the metal alloy due to excessive pressure from the striking of the coin.

The interesting thing is the toned line that runs out from the tip of the star from the 7 o'clock position. If your look closely, you will notice that the very tip of that star has die wear on it, somewhat visible from the flow lines running out from where the tip of the star touches the field. This natural die wear causes the metal to flow smoothly into the field in a way where the metal experiences less pressure than metal in the areas of the star that are perpendicular or squared off with the fields.

These squared off areas (like the arms of the star where the contact between the star and field are sharp - perhaps from a fresh die polish) cause the metal to undergo increased pressures and are enough to change the metal's atomic structure to become toning resistant. See how the toning looks all stretched out from the strike? Even though the toning occurred many years after the coin was struck.

Here's a great site about thin films and optical colors... it's a little geeky and technical but lots of interesting info there:

Understanding Interference Patterns in Soap Films

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