BIDDEFORD — One of two copies of the oldest known recording of a black vocal group in the U.S. is up for auction.

The recording of the Unique Quartet from 1893 is so old that it pre-dates vinyl recordings. The song, “Mama’s Black Baby Boy,” was recorded on a wax-covered cylinder using technology invented by Thomas Edison. It can be played only on a cylinder player that was a predecessor to phonographs, which played flat, vinyl discs.

Troy Thibodeau from Saco Bay Auction Co. in Maine says it’s the oldest recorded African-American music in the U.S. The cylinder came from the collection of a Portland man. The only other copy resides in the Library of Congress.

Thibodeau says there are so few of these rare cylinders that it’s difficult to place a value on them. Also up for auction on Saturday is an 1896 recording of the Unique Quartet.