1975 $100 Cayman Isle Gold Pc.-360 Deg. 1/3 Rim Layer Discoloration Diagnos

Finally, here are three additional shots that better represent the dark blue color that goes completely around the coin's rim.

That dark color is covering about 1/3 of the coin's thickness from the rev. side (five queen portraits) out toward the middle of the rim.






At this point I would be more than happy to know if this coin is 0.050 AGW. The grading details are secondary at this point in the discovery process etc.

I have done some calculating. Basic lower high school math.

Density of pure gold 19.32 g/cc
given: diameter 3.4cm, weight 22.681 g.

If pure gold, average thickness calculates at 1.174mm.
If pure silver**, average thickness calculates at 2.33mm.

I would assume that the density of .500 fine gold of around 16g/cc for this coin should yield a calculation of average thickness of around 1.75mm
Check measurement for thickness.


** density of pure silver 10.5 g/cc.
density of copper 8.93 g/cc.


Some guesses as to why the color banding:
1. The color band may be due to improper mixing of copper in the alloy.
2. Finely divided Silver on a photographic plate is black. Finely divided gold happens to be purple in color.