Slate question

Quoted text begins.inevitably, a large chunk will break off - or the whole piece will break in
two
End of quote.

Taunya,

I have produced edges on capping stones by stacking them flat, one atop the
other, wetting the stack and chipping the edges with a sharp 75mm bolster.

3/4" - 1" thickness stone will 'edge chip' best if the tile is sawn oversize
so that the excess material is between 3/8" - 5/8". Too little and the edge
will preserve the sawn surface, too much and the tile will break.

Mark the ends of vertical stack to the finished width and chip with hammer
and bolster while they are still in place, or stand each tile on a piece of
carpet to chip the ends across the thickness. Mark the face of the top tile
by joining the end marks and lay the tile back on the stack. Wet the stack
(I keep a hose trickling nearby) and chip the top surface of the top tile
to the line. Turn the tile over, join the end marks, wet the tile again and
chip the bottom surface.

The tricks are:
1. The correct amount of wastage in proportion to thickness of stone
2. Full support for the stone with a flat, heavier stone or a stack of
similar stones
3. Using water to help support the stone and transfer the shock to the stack
4. Striking the bolster with a confident blow
6. Chipping the ends first across the thickness of the stone
7. Chipping the face line by working from the outside of the stone to the
middle
8. Chipping the face surface first, then the back surface

Regards,
Simon