Tannic acid and iron

Deborah Wallsmith <deborah_wallsmith [at] mail__dnr__state__ga__us> writes

>...  Does anyone know what the
>consequences might be of using tannic acid on iron that may still
>contain salts?

I did some research into tannic acid a few years ago. Looking
through the literature there seems to be several cases where tannic
acid treatment was surprisingly successful in treating marine iron
that had not been completely desalinated. My feeling is that it
preferentially reacts with and helps to solubilise chlorides from
iron, though I did not test this. Anyway, it is not harmful to use
where salts are present (though the salts themselves may continue to
cause problems). Where very low chloride levels are present (as will
probably be the case with your objects), iron can be given
preliminary coat with tannic acid, rinsed with deionised water to
remove any solubilised salts and recoated with tannic acid.

Vanessa Roth


                                  ***
                  Conservation DistList Instance 14:60
                   Distributed: Tuesday, May 8, 2001
                       Message Id: cdl-14-60-001
                                  ***