in my opinion, the item upgrade system is bad because it's too big too little chance for success
.we should add the opportunity bar to 100% success.my suggestion is as follows.
leave the stones that are but change the value they give.that is, add the minimum value that they give and the maximum.and eliminating the destruction of the item
and only leaving an unsuccessful one that lowers his level .
and forgot to add the possibility to lower the level of the item