The periapt of proof against poison is indistinguishable
from ony of the other periapts.

The character who has one
of these magical gems is allowed a 10% saving throw per plus of periapt
against poisons which normally disallow any such opportunity, o normal
score for poisons which usually are at penalty, and a plus on all other
poison saves:
 

Die Roll	Plus of Periapt
1-8	+ 1
9-14	+ 2
15-18	+ 3
19-20	+ 4