Two types of air hammer with two chisels.
No evidence is available for this source.
Roundel and tooth chisel fittings for air hammers are shown here. The air hammer is a pneumatic device into which the carver inserts a range of chisel types. Rather than hitting these chisels any harder than a carver would, the air hammer hits them faster and allows the carver to work for longer before tiring.
No images in current category.