I agree with John, 100%. :thup:
As to the pwt, how big is it? If it's fairly massive, (12+ cm in diameter) it likely is earlier too.
Does your ink pot have a round/oval polished pontil mark? Is it marked Mdina in any way? - and if so, what does the script look like?
These have been found with both Michael Harris' and Eric Dobson's writing on.
And is it amethyst?