Valuing Old Coins
Lightly circulated coins
While the same grading principle applies from XF40 to AU58, that being we're still measuring wear, not every coin is struck with the same level of detail. At these grade levels the variance in detail from the strike depth is similar to the variance in detail from wear, so relying on detail alone to grade these is inaccurate.
XF40:
AU50:
AU53:
AU55:
AU58:
While it can be seen that detail still goes up with each grade, the areas which show missing detail vary considerably due to striking differences and it can be the case where coins show considerably less detail in higher grades due to being struck weakly. For this reason, the level of wear on the exposed surfaces need to be considered. This is best measured through how much original lustre remains.
Lustre refers to how a coin's surfaces reflect light. It is not to be confused with how much brilliance a coin has - brilliance is the original colour of a coin, so a toned coin has lost its brilliance, but its lustre should not be affected, except to the extent that the toning has worn the top layer of the coin.
The reason lustre is effective at measuring wear is because original lustre is shaped by the way light reflects of tiny grooves in a coin's surface formed there from when the coin is struck, and when a coin is worth, these grooves too are worth so a coin's lustre is lost with wear. Environmental exposure also wears away these grooves, particularly on more reactive alloys such as bronze, but such cases are the exception rather than the norm when it comes to coins in the XF-AU grade range.
Once a coin has full lustre, it means its unworn and should make an MS grading though care must be taken to look at how lustre flows over the coin's high points. In the case of the AU58-graded 1928 florin, lustre is full in the surfaces but breaks on the top-left of the emu, and the leg and shoulder of the kangaroo. The obverse is unworn but nonetheless this wear is enough to preclude a mint-state grading. It is still a respectable coin and if we look up its value we get a value of $190.
