New to alchemy in general, apologies if I say something incorrect.
I used a Cursed Infusion on a +5 Bow (might have been +4?) and it didn’t upgrade it at all.
After drinking 4 Potions of Experience to get to Level 30, the Bow only levelled up to +6 and stayed there after I removed the curse.
I’ve seen people get to +8 so I must have done something wrong.
You need to keep the curse or the extra upgrade gets removed as well.
Exploding curse works really good with spirit bow as the explosion takes place next to the target rather then where you are.