If you're wearing a lot of armor that causes bungling, or under the effects of some spells, your chance of botching the spell increases. The more armor you have on that can cause bungling, the higher your chance of bungling the spell. Some special kinds of armor allow you to cast spells without penalty.
Bungling the spell still charges you the spell points for the spell.
All non-cloth armor (aside from girdles and any boot), bungle. All gold, except for helm of brilliance, do not bungle. Most mages wear (crown/circlet/wizard hat), golden breastplate or wizards robe, or robe.
Don't affect spellcasting:
- Crown / circlet / golden breastplate
- Fancy white gloves
- Body armor
- Non-cloth gloves (gauntlets of dexterity, power etc)
- Helm of Brilliance (gold but still bungles)
- Leather armor aside from girdles, bungle slightly