We do not provide specification information for materials as these are formulas developed by our artisans.

looks like American Clay

Maybe American Clay "porcelina" or similar. I find it incredibly asinine that you would post your work here, and then deny an inquiry for the origin of the most prominent part of your photo. Disclaimer or no, it's rude.

is the fireplace material cement plaster? or render? hoping to do the same around my wood burning fireplace and still be safe materials with no toxins emitted when heated?

Idea, how about you recommend your artisan than, instead of spilling their "secrets"? You should be able to provide some kind of information if you are posting here.