Pam,
If you can do so, look at an affected area under a microscope (30-100X
should be fine).  It is possible that what you are seeing is fatty spew
or wax from a leather dressing.
 
If it is a leather dressing, VM & P naptha should redissolve it,
returning some to the leather and removing some.
 
If it turns out to be mold, treatment with swabs dipped in isopropyl of
ethyl alcohol will sterilize the mold and begin removing it.  Do no use
methyl alcohol on leather (or parchment) as it will begin breaking down
the collagen.  But first test to insure that the painted surface is not
alcohol soluble.  The leather dye may be an alcohol stain, but unless the
leather is flooded with alcohol, there will probably not be much movement
of the dye.
 
Jack C. Thompson
Thompson Conservation Lab
Portland, OR
 
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On Fri, 10 Feb 1995, Pam Endzweig wrote:
 
>   Yesterday our museum received a painted leather carrying bag from
> Mauritania (about 16 inches long and 7 inches in diameter).  Portions of the
> bag are appear to have gotten damp and exhibit a light shadow of mould.  The
> leather is otherwise in good condition, i.e. quite supple, and not at all
> stiff and brittle.
>
>   Could someone please advise me on a good course of action to deal with the
> mould?  I'm not sure whether to take a cold or a warm approach (though I'm
> much more favorably inclined towards low temperatures, given the condition
> of leather and the very detailed, painted designs).  I have not been able to
> find a solution that seemed appropriate in the reference sources I checked.
>
>
> Pam Endzweig
> Collections Manager & Staff Archaeologist
> University of Oregon Museum of Natural History
> Eugene, OR 97403-1224  [log in to unmask]
>
>                            Pam Endzweig
>              Collections Manager & Staff Archaeologist
>                 Oregon State Museum of Anthropology
>           University of Oregon Museum of Natural History
>          Eugene, OR 97403-1224, USA   Phone (503)346-5120
>                     [log in to unmask]
>