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archaeologist interested in CaCO3 stability on ancient terracotta

Question asked by Drew Brisbin on Mar 6, 2014

Hi, I am an archaeologist investigating some ancient terracottas and I have a chemistry question regarding the stability of CaCO3 at high temperatures.

 

Here's the story: I am looking at materials that have been white washed in preparation for the application of pigments. X-ray fluorescence spectrometry picked up high Ca peaks, so calcium carbonate was suggested as the source of the white wash. Limestone and travertine are common in the area, so perhaps it's in the calcite form? I am trying to figure out if the terracottas were white washed before or after going into the kiln. The kiln would have burned at 750-950 degrees C (and at atmospheric pressure and composition), and the pieces would have been fired for many hours.

 

Would a calcareous white wash survive the firing process? Or would it have necessarily been applied after baking?

Thank you!

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