Brown-Grey Burnished (BGB) is a Cypriot Iron Age ware that is highly polished and may or may not have an actual applied slip. It may simply be a highly burnished plain fabric. Or some pieces could be a lightly reduced Cypriot Red slip (Iron Age) that is highly burnished. When found in the form of a tiny sherd it can be hard to tell.
Polis/Marion, Peristeries (Princeton Grid Area B.D7) (Cyprus/Chrysochou Valley)