I'm a first time poster trying to figure out what I have.
About 30 yrs ago when doing yard work I dug up a ceramic/stoneware jar. It's white in color, very heavy for its size, and it has an unusual clamp that secures the top to the jar. There's a metal label on the top, most of the name on the label is worn off, but you can read the words Stoneware Company. The bottom of the jar has the letters BOF stamped in it. Between the top of the jar and the jar is a rubber seal.
Inside the jar is filled with what I would call marbles. They are solid in color, sort of a dull off-white / tan color. They are smaller than a dime, and they are not perfectly round, but a little rough.
I've attached a picture, hopefully it will help.
thanks!