Just learned this:
Concentric rings base (CR), circ: 1840-1880
This base type appears on pottery bottles and was formed when the thrown bottle was separated from the potter's wheel. A wire was looped around the bottle's base and crossed. As the wheel spun, the wire was pulled and sliced the bottle off the wheel and created a series of concentric rings on the base of the bottle.
from: http://www.sodasandbeers.com/SABBottleBasesBeer.htm
Concentric rings base (CR), circ: 1840-1880
This base type appears on pottery bottles and was formed when the thrown bottle was separated from the potter's wheel. A wire was looped around the bottle's base and crossed. As the wheel spun, the wire was pulled and sliced the bottle off the wheel and created a series of concentric rings on the base of the bottle.
from: http://www.sodasandbeers.com/SABBottleBasesBeer.htm