Hi,
the light coin to the left doesn't really look or feel like cu-ni, but what could it be?
Light coin: weight 2.63 grs, 19.97 mm in diameter and 1.38 in thickness
Normal coin: weight 2.73 grs, 19.99 mm in diameter and 1.33 in thickness
Those differences fall well inside the normal tolerances.
Ole
Unless the two coins are significantly different in thickness, they must be of the same metal, because the weight and diameter are the same. I suspect that the one on the left is over-cleaned and under-neutralised after cleaning and that a sharp acid was used.
Peter