It is thrown, then flattened to an ovoid shape and with a cut top to create an asymetrical form. Decorated with an icised pattern of psuedo runes ?
A very clever and well made monogram seal mark has been impressed in to the underside before firing. The monogram looks to read RC or CR or possibly RG or GR. A school room would not have gone to the trouble or cost of creating a seal, that might only be used once or twice. I have assumed that this is the mark of a potter set up to create "multiples" either a keen amateur or a more porfessional set up.
BUT WHO ???