Dear Eugene Morin,

When confronted with the problem of bones encrusted with what is also known as ‘calcrete’, I use dilute acetic acid (vinegar).

If done with care, the bone or tooth will not be damaged, I generally immerse the bone in vinegar and wait until the fizzing stops – generally after an hour or so. Then brush to clear away the clay particles and re-immerse in fresh vinegar if necessary. You may have to repeat this several times.

Then leave several hours in fresh water to extract all traces of acid. Then leave the bone to dry. And if the bone is fragile you may need to consolidate with a conserving agent like ‘Rhodopas’ (poly-methyl methacrylate or Perspex).

An alternative solution is to mechanically remove the calcrete with a ‘graver’ – a hard steel nib or needle (rather like the old 78 rpm gramophone needles) mounted in a hand-held machine that vibrates the needle in and out at high frequency and also used to mark metal products. My experience with gravers indicates that you have to be very careful as it can damage the underlying bone and even explode the enamel on teeth.

I know that vinegar was used with great success by Roger Miles at the British Museum of Natural history in the 1960s to prepare complete and articulating jawless palaeozoic fish skeletons from the limestone pebbles found on Gogo Farm in Australia – he showed me the spectacular results!

I’m afraid I have no idea what damage acid causes ancient DNA or Carbon isotopes, but I would guess that radiocarbon dating may have to ruled out. You will need to ask a chemist!

Hope this helps,

Simon Davis

Dear zooarchers, I’m currently looking at a collection that comprises a few specimens that are partly covered with calcareous concretions. I was told that these concretions will dissolve in a water-based solution that contains acetic acid (vinegar). Does anyone knows if this can damage the bone or affect subsequent analyses, including radiocarbon dating and DNA analyses?