Serial#: 17938. The Martin 0-21 was the first (and smallest) of the company's three 0-series, or "Concert Models." This is a slot head instrument having the twin rounded slots on the headstock that many associate with classical guitars, but in fact it is braced for extremely light gauge steel strings. Its headplate is derived from Brazilian Rosewood veneer; the back and sides are solid Brazilian Rosewood, and so is the heel cap. The back stripe is wood mosaic in the herringbone pattern and so also the center ring around the round central sound hole. The top is bordered in four-plies (thin inlaid lines) of ebony and what might be spruce, while the back is decorated with only one-ply of spruce.

The ebony unbound fingerboard is inlaid with the short pattern of four etched diamonds in Mother-of-Pearl on frets 5, 7, and 9 (double diamond on the 7th). The bridge is carved of ebony and has a wooden carved "pyramid" on each side. The back of the neck is "V-shape." Since Martin did not make the transition to a decal headstock logo until the early 1930s, this guitar instead has "C F Martin & Co., Nazareth, PA" stamped on the back of the headstock.

VG; refinished; endpin missing, period correct bridge replacement, original bar frets, several cracks on back