“…5c). We ascribe such compositional heterogeneity to compositional cords, well-known in industrial glass synthesis (Geffcken, 1957;Bondarev, 1965;Shelby, 2005). Compositional cords are often ribbon like in three dimensions and can be created by either differential volatilities of some metals, incomplete melting and homogenization of glass chips, or possibly by deformation during formation of miniscus of the melt-gas interface.…”