Odd, but this is the second of these I've found in the past month or so, perhaps both having come out of the same estate somewhere. It's a rare one—the 20th ball in a c. 1880s set of baseball pocket billiards, which is the only sort of billiards set that contains 21 balls. (Typically billiards and pocket billiards sets contain 15 marked balls plus a shooter.) I believe this ball was designed and produced by George H. Burt of Millburn, NJ. as I have found documentation of a few standard sets out there made of clay and engraved in just this manner (with individual balls going for $100+ a pop). So, rather special—and, again, I think a perfect birthday present, in this case for someone turning 20.
2 1/4” diameter, numbered on both sides. Both sides documented. Surface cracking and wear to the clay and to the black of the engraved numbers as evident. The color is a pale orange.