I recently used a dilute aqueous solution  (5%) of thioglycollic acid to
remove hematitic encrustations from a chert tool.  I adapted Francis
Howie's method for removing iron compounds from vertebrate fossils, but
left out the buffers Howie used to protect the bone from phosphate loss.
 Anybody see any problems with using this method to remove iron
deposits from chert?  Any other methods used by archeological
conservators?