After months of wrangling with the developers and years of rumors we finally have definitive information about the upgrade formula's that go into using stones and runes to upgrade items. Read below for all the juicy details:
Smelting Stones (regardless of level)
Chance to Upgrade = 50% - an increasing amount for each + past 0
Chance to Break = 50% + an increasing amount for each + past 0
Chance to Upgrade = 60% - an increasing amount for each + past 0
Chance of no change = 20% + an increasing amount for each + past 0
Chance to break = fixed at 7%
Chance to degrade (-) = fixed at 13%
Q: Do ROP I, II effect the %'s in any way?
A: No. The rates listed above are unchanged regardless of using a ROP.
Q: Is it possible to break an item at +14?
A: Yes the chance to break is fairly high with a smelting stone and fixed at 7% with a HS.
Q: So it's easier to upgrade items the higher the + is?
A: No it is harder, the % to upgrade reduces each additional + added to an item.
Q: So what about upgrade events? What does 200% Upgrade mean?!?
A: An upgrade event alters the initial % value (50% for Smelting, 60% for HS) but it does not alter the subtracted value. What this means is that beyond the first few +'s there is no 100% even during a 200% upgrade event.
I am in the process of getting the same information for the new upgrade runes (purified and devil) and will post them when I get a chance. We will be changing the website and in game descriptions to reflect these revelations ASAP. Until then please spread the word to your fellow players, let the truth be told