i. We do not know what makes these - the two theories are discussed.
ii. 1958 and 1959 are not the only two years these are known for.
iii. Other denominations can have the same "Black Beauty" appearance.
iv. A Black Beauty's luster/color is notoriously difficult to capture on film.
Resource (Likely the best on the internet):
Here is a long thread having everything you ever wanted to know about Black Beauty nickels from a specialist who collects/researches them:
https://www.coincommunity.com/forum/top ... _ID=288744
1. Best two theoretical causes (mentioned in first post at link above):
- a. Improperly annealed planchent.
b. Improper alloy mix with possible annealing oven variances.*
One note needs be mentioned before proceeding:
A main problem with Black Beauty coins is they are notorious for not being able to be photographed properly showing their dark luster (as is repeated in that link).
Following is a picture from the above thread of another specialist's collection of BBs which include a 1954 and a 1955 alongside numerous 1958s and '59's. Since the collector mentioned has so many legitimate Black Beauties and can compare the '54 ad '55s side by side, I tend to give ANACS the benefit of the doubt that they got it right with the 1954 and 1955 (not being facetious).
Here is one of the 1955 BBs:
3. There are also other coins with the same Black Beauty appearance that are not nickels! Here are old and lousy pics of my quarter I posted to that Black Beauty thread as well as a link to the where my post is:
http://goccf.com/t/288744&whichpage=8#2715180 Note the first two pics were taken with direct sunlight hitting the quarter , but the picture, somehow, killed the luster. The second set of pictures is the same quarter beside a normal one and better shows the "Black Beauty" looking quarter to have the black luster a true BB has (still not a good pic).
Looking at the first pic you actually can see the cartwheel luster making the typical hourglass shape from top to bottom. I think the unusual color makes the luster easy to miss in those two top pics.
Why the color difference in the two pics? Ask the camera. While it does have a slight bluish cast in direct sunlight I think the camera over-emphasized it.
Note - if the theory Black Beauty nickels are an allow mix problem and not an annealing error, then the quarter posted would likely, and technically, not be a Black Beauty b/c the quarter is most likely an annealing error (sintered planchet) and not an alloy mix problem.
* A Black Beauty might be a product of an incorrect annealing process, too much or too little oxygen in the coin, and maybe a trace element in the alloy mix. Sintered planchets are not colored all the way through but surface-affected only. An alloy mix error, by definition is all the way through the coin.