Preserving in stone jars

Similar but not quite the same, I have a Rumtopf (which you fill gradually over the season with layers of different fruits and keep covered in good strong spirit at all times to use at Christmas) and the lid doesn't fit that tightly. I seal it with clingfilm then put the lid on top and this works well.

You might try clingfilm with a weight on top of it, but brown paper and string might work just as well for a sealed once until you use them preserving.

Thanks for your replies. I suppose it won't need to be airtight will it.