Murray--

Clawhammer banjo is as you describe it--using the nails (actually a particular nail, usually a bit longer than the others) to brush the strings--usually two down strokes and then a pick-up with the thumb on the fifth string. No picks are required. Clawhammer style is not limited to open-back instruments. In my part of the country, folks played whatever was available through the Monkey-Ward or the Sears catalogs or from local sources, and it was availability rather than style which ruled one's decision. Many of the old-timers I knew growing up provided their own resonators in open-back banjos by inserting a pie-pan in the pot. Old-time fiddle players, especially the older ones, seem to prefer a clawhammer banjo as a back-up instrument, as the style accentuates the down-beat, and provides a percussive sound not unlike a brushed drum. I learned the style from a fine gentleman known as Uncle Arthur Kuykendall, who used a "drop-thumb" style in which he used his thumb on all strings rather than just the fifth.