Plano-convex ingot Plano-convex ingot Plano-convex ingots are lumps of metal with a flat or slightly concave top and a convex base. They are sometimes, misleadingly, referred to as bun ingots which imply the opposite orientation of concavity. They are most often made of copper although plano-convex ingots of other materials such as copper alloy, lead and tin are also known. Plano convex ingots are found across a wide chronological and geographical range with the first examples known from the Near East during the 3rd and 2nd Millennia BC. By the end of the Bronze Age they were found throughout Europe and in
Compound refractive lens Compound refractive lens A Compound refractive lens (CRL) is a series of individual lenses arranged in a linear array in order to achieve focusing of X-rays in the energy range of 5-40 keV. They are an alternative to the KB mirror. For all materials the refractive index for X-rays is close to 1, hence a single conventional lens for X-rays has an extremely long focal length (for practical lens sizes). In addition, X-rays attenuate as they pass through a material so that conventional lenses for X-rays have long been considered impractical. The CRL gets its reasonably short focal length, on