Acid

If a thief is faced with a lock which his best efforts cannot pick open, metal-eating acid is one alternative. Such acids will eat through locks if the locks fail a saving throw (for metal) vs. acid (this save is 13). If the save is made, the lock cannot be opened, but it will be ruined (and unopenable!) if a second save (metal vs. acid) is failed. Use of such acid is difficult and avoided by most thieves, for various reasons.

Use of metal-eating acids is difficult because only acids of great strength will do the job effectively. The DM should greatly restrict the availability of such acid; acids of the strength of black dragon acid and thessalhydra acid (possibly also giant slug spittle) are among the few known effective metal-eaters. Thus, availability is very low (and cost very high).

Thieves usually avoid such acids in any event. First, the acid is very hazardous to carry. While it may be contained in glass containers (and possibly ceramic), such vessels are fragile. Imagine falling down a pit and hearing the sound of breaking glass as double-strength acid begins to seep through clothing and over one's back . . .

Second, if the acid does not do the job it may ruin the lock and any hope of opening it in another way, as described. Third, it is a calumny on the professional reputation of a thief to have to resort to such means as acids!