![Penumbra](http://americanglassroots.com/cdn/shop/products/BRod-Penumbra-2T_a23e076d-7c15-440f-9b92-2779ba836ca7_large.jpg?v=1453250520)
Penumbra
Named for the shadowy edge of a lunar eclipse, Penumbra is a reactive “silvered” cobalt blue, reformulated from one of Paul’s old favorites. Different colors are produced from reduction or oxidation, primarily a wide variety of blues and greens. Reduction can create a luster that you can trap under a clear encasement. However, surface haze doesn’t burn off as easily as amber/purple type glasses.