Earthenware ceramic

Helen Privett <helen.privett [at] ngv__vic__gov__au> writes

>I am currently treating a Tang dynasty cream coloured earthenware
>figure of a horse.  The figure has previously undergone extensive
>restoration including the insertion of approximately 4mm diameter
>ferrous dowels into each of the legs; each leg having been broken in
>at least three places.  ...
>... removal of the plaster layer has revealed ferrous staining
>to the cream coloured earthenware.  Has anyone any experience with
>removal of ferrous stains from unglazed earthenware ceramic?  Is
>this possible?  ...

You might try 2-5% ammonium thioglycolate (mercapto-acetic acid and
ammonia brought to neutral pH) for removing the iron stains. I've
not tried it on ceramic, but it sometimes works well on marble and
porous stone. The ammonium thioglycolate will turn the stain purple
and will flush out easily with water and/or dilute hydrogen peroxide
(3%). It smells nasty like hair remover (Nair) but sometimes works
like magic.

Susan White
White Conservation Services, NYC


                                  ***
                  Conservation DistList Instance 16:30
                Distributed: Wednesday, October 30, 2002
                       Message Id: cdl-16-30-007
                                  ***