The base photo does not show the detail needed to determine how it has actually been finsihed. Is the "ground" area all grinding or is it at least partly age wear? Is the central area a simple, single cracking off scar or is there more to it than that? Are there any "cutting in marks" visible in or around the "ground" area? Is the base flat, indented or raised in the middle?
Too may queries to make any guesses.
As for the orange ... there were many variations in the shade of orange seen in finished Ysart items and there was also variation in how "smooth" or "crunchy" the grounds were. I suspect that much of the reason was a difficulty in maintaining a "standard" orange colour as it was apparently quite hard to control when being worked.
Different shades and textures of "Ysart orange" could be a good collecting area for somebody.