Also some amount of yellowing and crazing (crackling of the glaze) are all normal for such an old piece and should not affect the value. You've got multiple hallmarks there, and we're really going to need big, high-resolution pictures to make them out. Those blue circular ones and the text above the maker's name. I can't tell in the last image if those are letters or numbers, but I'm old as dirt and blind as a bat, LOL
There is a impressed rectangle above the green hallmark, which says "Iron Stone China" [middle] and below that "Warranteed". Above Iron Stone China, it possibly says Elkin Knight & Co.
Because it's white on white, I doubt it won't show up with a macro pic.
I have no idea why the Flow Blue type dots are there.
Thanks again to all, for the information.