The Bartell company was formed by former Rickenbacker, Magnatone, and National employee Paul Barth (engineer) and Ted Peckels (owner and company president, shown in the pic below) in the mid 1960s after Barth returned from Magnatone's facilities on the East Coast. Bartells were produced from 1964 to 1969, and Peckels estimated that around 2,000 instruments were produced. The Bartell company also rebranded their products for Hohner, St. George, and Lancer. This was Paul's second guitarmaking venture, with the first being Barth guitars in the mid to late 1950's.

Probably a good 90% of the Hohner-branded basses I've seen so far have been black but I have seen a few natural finish and even 1 or 2 sunburst ones. 99% of those have been fretless basses.  All featured a plain black vinyl pad on the back.  The 2 Bartell basses I've seen so far have both been fretted instruments with a yellow-green vinyl pad on back, the same material I remember being used for kitchen chairs when I was a kid.