You need to stabilize the rust before putting any coating on the cast iron
stove. To simply coat over it will allow the deterioration to continue -
probably at a slower rate.

Cast iron contains core metal that has a stable grey oxidation (Fe3O4 -
magnetite) from it's thermal history of manufacutre in a foundry. Additionally
historic cast irons can have patinas of iron oxides ranging from brown to
reddish-brown and black, as well as historic coatings, and soot and ash deposits from
use. So all this must be taken into account before cleaning - you never-ever
want to clean below the stable grey magnetite into the core metal.

You also need an experienced eye to examine the stove to see if this really
is "rust".

Get a very bright direct light on the surface and look for various shades of
brown, orange, and red that are associated with surface features like pitting
or even delmaination (in severe examples). Using low-power magnification helps
(even one of those magnilights on extention arms).

You may notice a bright orange layer that goes over and covers details and
over pittting - this is often seen under or at the edges of paint or coating
layers. This is NOT corrosion, it is most likely a red lead paint primer - and as
such it is HAZARDOUS and should only be removed by someone who is trained.
Red lead was used ubiquitously on metals from the 18th century up until the
1970's (at least in America). I have often seen it on architectural metals
(hinges, crossties, weathervanes, etc) and sometimes on cast iron wares (pans,
stoves, firebacks, etc.).

In terms of coating cast iron stoves much depends on if a historic coating is
present, the condition of the object its environment, if the stove will be
used, and the sort of appearance (aesthetic) that is appropriate. The coating
choices can range from non-ionic oils, to pigmented micorcrystalline waxes, to
stove blacking (an historic coating appropriate for stoves in use - contains
graphite usually bound up in a parrafin/solvented base).

I try to stay away from paints on stoves or firebacks because their thickness
clogs up and obscures decorative details and paint removal can sometimes be
difficult in future years. In these situations you need to understand what
coatings were applied historically and to find its comparable modern counterpart
that has the stability that we conservators like to see in the materials we use.

Cheers!
Dave

David Harvey
Artifacts
2930 South Birch Steet
Denver, CO  80222
303-300-5257
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