How does the cap on Materia work?

[LuBu]

I can't help but notice that when you meld stuff, there seems to be a hidden cap that once you reach over, you don't get stats for them anymore (For instance, a friend told me this ring can only be upgraded to have certain stats +4 control +4 craftsmanship and anything over would make the materia lose effect)

Can anyone chime in on this? Is there a list somewhere about all that? I have a feeling it is all based on ilvl...

[Urthdigger]

It's based on ilvl and the slot used, with different stats all having different caps (For instance, piety has a slightly lower cap than other stats).

The most important thing to keep in mind, however, is that these stat caps INCLUDE THE EXISTING STATS. In the case of a HQ item made for DoW/DoM, all the stats on the piece will already be at cap, so materia can only add stats that weren't on it originally. For HQ items made for DoH/DoL, the stat caps are actually fairly higher. NQ items are the same as HQ items, just with lower base stats, the caps are exactly the same.

Another thing to keep in mind is that if you, say, try to add a +4 materia when the cap is 2 more, you will still get the +2 stats. This can be useful to know in certain cases where a higher level materia is easier to get your hands on than a lower level one.