Hello! 1st of all you do not mention if the ring is yellow or white
gold. 2nd you did not mention if it (the ring) was breaking the
finger out as to an allergy, along with the color of her finger. Next
you should take it back & have it cleaned & steamed again to make
sure that they (the maker) just did not leave a little polishing
compound inside the ring. (the simple problem) If this does not help
& the ring is white gold your wife may be allergic to white gold
(nickel). A change in medication can also cause this. Some hand
lotions with skin softeners, which contain small particles of
abrasives that smooth hands, can abrade the metal as well, that will
appear as blackish smudges (actually the particles are so small they
do not reflect light) & they appear blackish. Many things other than
a poor product or jeweler can cause this. After 35 plus years as a
bench jeweler, I have seen & cured this problem and many more!
Been there, done that.