Removing stains from stoneware

I am working on a children's stoneware ceramic tea set, decorated by
a pink transfer pattern.  The ceramic body was stained brown which
had entered the body through cracks in the glaze.  The treatment
steps included wetting out the objects with water prior to
poulticing with Laponite.  Soaking in water alone turned the water
tea brown and the ceramic body felt slimy.  Despite the large amount
of staining leaching from the object, staining was only slightly
reduced and several successive Laponite poultices were applied. The
Laponite gel also became very brown, however the staining was only
mildly reduced.

I am now considering what other methods I can try.  Both tea or
coffee stains are coming out of the objects and pustules of white
have also appeared.  I am assuming that this is milk fat? I have
looked into enzyme methods of cleaning, but feel that this will
damage the crazed glaze.

I am wondering whether an alkaline treatment would be suitable, but
am uncertain what strength I should use it at and should it be
poulticed or soaked? Has anyone had success with ammonia, I am
familiar with its use at a low percentage to cut greasy and fatty
residues, but cannot find any recommendations to use it at higher
strengths or whether soaking will damage the ceramic body.

Holly Jones
Objects Conservator
Artlab Australia


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                  Conservation DistList Instance 14:12
                  Distributed: Friday, August 11, 2000
                       Message Id: cdl-14-12-014
                                  ***