|one stone in 1 slot|
I put my gems inside items and then put those items in 1 slot. In that way I can hold 4 gems in 1 slot (+ 1 item). Maybe a screenshot will make it more clear. The only disadvantage is that you need to pay gold at the jeweller to get the gems out. But for high level players, gold isn't a real problem I think.
|several gemstones in 1 slot|
It's seems obvious to pick an item with 4 slots. But writing this article I learned something myself, while reading the wikia page of drakensang. Adding one slot to a plain item only costs 10 andermant, to an improved item 20 andermant. So I think it's worthwhile adding one slot to these items. You can see on the screenshot I hadn't done that (only 4 plain slots). But after realizing this, an extra slot was added quickly ;)
I hope this helps those who have a shortage of inventory or vault space.