It's actually quite interesting how careful handling of pottery can be done with hopes of recovering uncontaminated carbon residue for radiocarbon dating certain pieces. Sometimes blood residues from stone tools can identify the animal being butchered and some stone tools can hold info. on which plants were being processed. The data recovering process is not within my playing field here for sure.
A lot of things have changed recently, always be on the safe side and look to the future when washing/handling artifacts. Not sure why you got rejected, but it's not cheap and many have very limited resources, unfortunatly.
Thanks for posting,
BCI