Because it's an item, like i've explained you earlier, goto the +.. item and put in refine_proto the new item (after upgrading).
For an example, the stone goes with itemA+1 to itemB+2 with (x)refine_vnum (the item where it turns into) and refine_set (upgrade material list)
Open in your database Player -> Refine_proto and add a new line with the (x) refine_set you had setup in your item, and choose which vnum, items and coins are needed to make the upgrade, in this case coins only because it's a stone.
Succes Mor