We are preparing to restore an historic covered bridge, built in 1881 and
according to the original specs, painted with "brown fire-proof paint".

Has anyone researched fire-proof paint?  We have found several references
to it and even a few recipes (all with very different ingredients I
think--one based on lampblack, graphite, manganese oxide, , turpentine,
linseed oil etc.--another on slaked lime, alum, rock salt, copperas,
potash, sand or hickory ashes).

Is there a common thread here??  Any ideas about what pigments would be
mixed with either of the above to produce brown?  Any suggestions would be
appreciated.