Tools for very hard stone

["Jane Mortimer" <jane@zzzzzzzzzzzzzzzzzzzzzzzzzz>]

I am currently working on a sculpture in Kilkenny limestone, which is
extremely hard.  I have resorted to roughing out with an angle grinder and a
heavy duty punch, which is working quite well, but for the more detailed
carving I don't know what best to use.  I did an earlier sculpture in the
same stone and broke the teeth on an ordinary replacable head claw, and also
broke a very sturdy 1/2 inch tungsten tipped masonry chisel. The tools I
normally use are a set of marble / limestone tungsten-tipped masonry
chisels, and a set of tungsten-tipped fine carving chisels.  I am wondering
if the solution is to get hold of some granite chisels, or whether there are
other options.  For example, would using pnuematic chisels make any
difference?  I got on quite well using a small tungsten-tipped point after
the grinder, but I want to be able to polish the sculpture once it is
finished, so I need something that will smooth out the rough marks without
breaking.  Any ideas / suggestions would be most gratefully received.Thanks

Jane