Agate Platter that I know nothing about!

This platter was my grandmothers and would have been acquired sometime before 1978 and possibly a long time before. It is 26cm x 16cm and is quite heavy. I can't see a mark although I have included a photo of an area on the base that is quite scratched and I can't decide if something is written there or it is just scratched. Its a long shot but i would love to know more about it

It looks professionally made, but I’m afraid without a mark it’s difficult to pin down to one particular potter or pottery. All the slipware potters used similar clays and dish shapes.

Thank you, both