Core band 1 color should be 10R 4/2 Weak Red only. This fragment is likely a bread mold or oven fragment. The rectangular shape combined with the very large, really grit inclusions combine to suggest bread mold. This sherd in fact consists of two mending fragments. Black staining on the internal surface also supports the baking/cooking use. There are wavy, linear markings on both surfaces. The more concave surface is considered here to be internal. A very long void in the internal surface appears to be from the burning out or removal of a large piece of straw or string. Breaks are fresh and rough.
From Interior to Exterior