I think I spent about 20 minutes using the sand blaster or air scribe on this Mississippian period blastoid. It is from Sulphur, Indiana and about 5 cm in length. It was given to me with one side exposed in a rock but after I cleaned it with a water jet it came out of the rock revealing a flattened specimen.
I think the formation is Indiana Springs and the matrix is soft so the jet of sand/dolomite slowly began removing material from the fossil. Below are before and after images of each side. I took these in a workshop at night in fluorescent light so the detail is not great.
This is a very cool tool that requires patience and attention to detail.