Rust dust looks like a fine metallic powder
similar to dust of appearance or other
magical dusts. It is usually contained in
small silk pouches for dispersal by hand, or
in hollow bone tubes for spreading by blowing
through the tube. If it is shaken out by
hand, one pouch will cover a 10' radius
area; dust blown from a tube will create a
20' long cone, 1' wide at the start and 15'
wide at the end. From 1-10 containers of
either sort may be found at one time.

Any non-precious metallic materials
within the area of effect of rust dust will rust
(or otherwise deteriorate) and fall into useless
scraps one round after being contacted
by the dust. Precious metals (gold, platinum,
and silver, for instance) are not affected.
Objects of iron, copper, bronze, tin,
and similar metals or alloys thereof --
including mithral and adamantite -- will be
affected automatically if the item of which
the metal is made is non-magical.

Magic items (swords, armor, shields,
rings of protection, etc.) must save as if
struck by a rust monster, gaining a 10%
chance to withstand the dust for every
"plus" of enchantment; thus, a +4 sword
has a 40% chance of not corroding. Magical
items or objects without a "plus" rating,
such as an iron flask, iron golem, or ring of
spell storing, have a 10% chance to save
against the dust. All such saving throws
must be re-rolled every time a new dose of
rust dust is encountered.

Experience Point Value: 1,000
Gold Piece Sale Value: 5,000

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Undispellable
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Dear Dragon: 
I have a question about rust dust (issue #86).  If 
a dispel magic is used upon the object that has 
been deteriorated by the rust dust, will the spell 
alter the effects of rust dust? 

Jason A. Dunham 
Delmar, N.Y. 
(Dragon #91)

Sorry, Jason -- that seems like something that's 
beyond the power of dispel magic to accomplish. 
If the dust has taken effect and run its course 
(which only takes 1 round), the rusting process 
cannot be reversed, except possibly by a limited 
wish or wish spell.  Dispel magic won't undo the 
effects of magic once they have taken place; for 
instance, it won't un-burn something that's been 
hit with a fireball spell. 

Dispel magic might be useful if an object has
just been introduced to rust dust. If the spell can
be gotten off within the one-round period when
the rusting is occurring, it will (if successfully
cast) negate the effect for that single round. If, at
the same time, the item is quickly moved outside
the dust’s area of effect, it would be saved. To
determine whether the casting of dispel magic
succeeds in a case like this, figure that it’s being
used against 5th-level magic (since a rust monster
has 5 hit dice). Or, you can avoid the whole
question by ruling that something affected by rust
dust falls into the category of “a specially enchanted
item” (as per the dispel magic spell
description), and thus dispel magic can‘t affect it
in any event. 

— KM
(Dragon #91)