Removing tide lines from leather

In Cons DistList Instance 9:48 Sue Maltby wrote :

>I was wondering if anyone on the list has had any experience/success
>removing tide lines from leather.

As "one of the book people", I indeed encountered this problem many
times. The problem you describe is exactly similar to what happens
to books when they have been standing for a period of time in water
or on a moist surface (like soil or cellar floors). Being a
hygroscopic matter, leather soaks up the moisture, transporting all
kinds of particles which seems to be pushed forward to the
borderline between dry and wet parts of the leather. This is one
explanation. Some people suggest (mainly people concerned with paper
investigation) that it is not the particles transported by the fluid
but merely an oxidative reaction taking place exactly on the
dividing-line where the substance (i.e. leather) is drying. The
result should be a discoloration.

Now, what to do ? As from here I'm not able to see and feel the
object, it is hard to give any substantial advice but from my own
experience I know that (as you mentioned) when the leather is soaked
it becomes hard, darkish and most times brittle. Furthermore it
seems that this kind of leather takes up water even faster than it
did before (it seems some of the tanning agents get washed out...);
which means that it is even more difficult to treat.

I once had a case in which the leather was drenched and after
drying, showed a white cloudy line. Although the leather had been
severely wet, it was not affected as described earlier. The (tide)
lines which were there could not be wiped of with a cloth so that
indicated that the problem was in the leather, not on the surface.
Remarkably I could remove it with a little bit of starch-paste on a
piece of cloth/paper. Repeatedly rubbing and changing the cloth did
the job. It left no stains, but I'm sure this only works with
unspoiled, "virgin" leathers.

In cases were the leather was not in
such a good condition I sometimes tried to lubricate the concerned
spot with leather-greasing compounds like the "British Museum
Mixture" or the CLKB-recipe (developed by the Central Laboratory
for the Investigation of Artifacts of Art and History in Amsterdam,
and the Royal Library in The Hague). The main purpose of these
products is to refill the amount of natural fat to an initial level.
They are not intended to be a cleaning agent but still they
sometimes work that way--or the substance softens the leather in
such a way that the particles that form the tide lines are set free
so that they can be removed easier afterwards.

For all the methods I mentioned: be careful. Always do a little test
on a spot which will not show, and be aware of the consequences of
adding substances to leather. There is no ready-made solution for
this kind of problem, I guess..

Cor Knops
Knops Boekrestauratie
Groenstraat 8
6151 CS Munstergeleen
Netherlands
+31 46 529643
+31 46 511822
Fax: +31 46 529643

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                  Conservation DistList Instance 9:49
                Distributed: Thursday, December 14, 1995
                        Message Id: cdl-9-49-006
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