I believe the black is a type of pitch used in metalworking. I have several old sets that still have the pitch in the form. Often you'll find menuki with most of the pitch carved out, sometimes there is a signature under the pitch other times not. When I watch metalworking videos it is seen throughout the carving and shaping as the item is stuck in place, heat is then used to relieve the piece when completed.
To the age, I don't care if they are recent as many fine contemporary works are currently being made. There was a recent peacock kozuka handle made last year by a new artist that took a very high award and the piece sold for around 20,000 euro/dollars. I currently follow the artist and he is currently making a matching version for submission again.
I do not have an XRF gold x-ray, but by weight for size, they appear to be solid gold.
The rest is unknown, it was purchased based on the perceived quality, and my research has ended up short on the artist.