Odor in cow hide

On behalf of a private owner, Sue Valis <suev [at] austmus__gov__au> writes

>    I have recently purchased an African drum with a cow hide
>    playing surface. It appears that every time there is higher
>    humidity, the drum develops a particularly nasty odour.
>
>    I have gone back to the place of purchase, only to be advised
>    that I should rub some salt into the skin. Can anyone offer an
>    explanation for the smell and a way of getting rid of it.

At a guess, the hide was urine tanned. From Lotta Rahme's book,
Leather: Preparation and Tanning by Traditional Methods, The
Caber Press, Portland, OR 2001,  p.92:

   "Urine tanning chemistry

   "Within the leather trade, urine has been used for dehairing
    skins, for tanning skins and for washing skins.

   "Urine contains formic acid and urinase, and uric acid, among
    other things.  These acids have a preservative effect on the
    skin.  When urine is left to stand ammonia is formed, which is a
    strong base.  If a hide sits in urine for some time, the basic
    environment will begin to have a dehairing effect.

   "The ammonia influences the skin by splitting the naturally
    occurring fats, to form glycerol and free fatty acids.  These
    free fatty acids can penetrate the hide and react with the
    fibers of the dermis; the skin is tanned.  When ammonia is used
    as a cleaning liquid, it is it's saponifying properties that are
    being exploited."

Jack C. Thompson
Thompson Conservation Lab.
7549 N. Fenwick
Portland, Oregon USA
503-735-3942  (phone/fax)


                                  ***
                  Conservation DistList Instance 15:69
                  Distributed: Tuesday, April 9, 2002
                       Message Id: cdl-15-69-002
                                  ***