From Mumepedia

[edit] CORRUPTING

If you are darkie and got some anti-evil item into your hands, then it's not just crap anymore. You can corrupt them on black altar at ABR, or give to BN sage, and make them serve you as true servants on your evil paths.

Original	Result	'Place'
white robe	black hooded cloak
grey tunic	black hooded cloak	Sage
sapphire ring	banded ring	Altar
bright red amulet	black amulet	Sage
mithril circlet	twisted crown	Altar
crystal phial	?
necklace	increasing of Sauron's darkness	Altar
pale blue stone	azure scroll	Sage
ancient dwarven shield	defiled dwarven shield	Altar
whitie legend staff	charred staff
dunadan blade	wightblade