I would contact the experts at the Paleontological Museums world wide, and find out how they remove rock from bones that turned to rock.  You first want to test to see if that acid dissolves the fossilized bone too.

Limestine is calcium carbonate.  Nature changes Calcium Carbonate to Calcium Sulfate by making a dilute Sulfuric acid solution from Hydrogen Sulfide and water.  The process makes Gypsum, and Cave Passages.  Gypsum is much softer than limestone.

Thanks Michael, i am working under the guidance of my supervisor here at the ANU who has experience in the technique. It does seem that the bones are a little harder so they stick out and can be coated with paraloid before they go back in the bath.

Hello Alex,

you have to find out if the acid-concentration is the best for your material. Usually formic acid is used for bones in concentrations between 4 and 10%. Please consider, that formic acid has to be buffered with tricalcium Phosphate ( min. 10 g per Liter), because the acid extracts the Calcium Phosphate out of the bones. so bones and teeth get brittle and blue.

The Maximum time to let the samples in formic acid is 8 hours. then the samples need ca. 4 times more watering with fresh water.

Covering the bones with Paraloid is ok.

If you are not satisfied with the Treatment of the bones maybe the use of acidic acid is  worth a try (same principle with buffering).

Yours

Angelika

Hello Alex, 

It would be strongly advisable for you to dilute the acid; the concentration of it should be of ~10% acid and ~90% water. With Chalk echinoderms I generally use slightly diluted acetic acid, but given the fact that this is bone, I confirm strong dilution would be necessary.

Hope this helps.

Christian.

Hi Alex,

another comment from me I forgot above:

If possible please use mechanical preparation to remove Sediment. In this way the treatment with acid needs less time. The watering and watering-time between the acid baths is very important for permanent good results.

If you have further questions please contact me

I always use acetic acid. In my experience formic acid damages the bones.

Thank you very much for your answers. I am using around 5-10% concentration formic - but i am interested in your note about brittleness Angelika, in fact i have noticed the bones are becoming brittle after treatment, i will get in touch about using Calcium Phosphate. Acetic is another option to explore. Thank you.

alex