Carving Stone ??
Planning:
There are two basic approaches to carving. The
first is to find a stone with a distinctive shape or color pattern that
suggests sculptural forms. This approach frees the carver to follow the
natural forms within the material. The qualities of the stone itself
become a major influence in determining the direction of the sculpture.
The second approach is to begin by working out an
idea for the sculpture in drawings or by modeling a maquette in clay or
other easily worked material. Modeling in clay first, when you can add
and subtract material, push and twist the forms around, and try
different form combinations, frees the carver to develop the sculptural
idea without worrying about taking off a chunk of stone that, as ideas
change, he might later wish to have back.
Lay Out:
Before you begin carving, look at the stone to
determine the direction of the bed, or grain (similar to wood). In
sedimentary, metamorphic, and to a lesser extent, igneous stone, the
stone was formed by the accumulation of roughly parallel layers of
material built up over time. Wetting a sedimentary or metamorphic stone
with water will help display these bed lines, often appearing as
distinctive color patterns.
Stone will tend to break more easily when split
along these bed lines, like opening the pages of a book. And, like
trying to tear a phone book, it is more difficult to break (or tear),
and breaks less predictably when the direction is perpendicular to the
bed lines.
As in laying out a design for a wood carving, with
stone you must also consider the direction of the grain to ensure the
structural integrity of the parts of the carving. Try to keep the grain
running with the length of the design, and avoid thin projections that
protrude parallel to the grain.
Once you have determined the direction of the bed,
check to see if there are any hair-line cracks in the stone that could
open up and break off later during carving.
Now begin drawing your design on all sides of the
stone. Make sure to project the same height and width of each form on
to the other sides of the stone.
Roughing out:
The quickest way to remove a lot of stone form a
block is with the pitching tool. To use this tool, the stone must have
a flat surface and squared corners. Place the pitching tool about 1
1/2" from the edge of the stone. Hold it straight up and down, then
tilt it back slightly so that the force is directed towards the area
you want to break off. With one sharp blow, break off the edge.
After removing as much material as possible with the pitching tool, begin to define the shapes with the point chisel.
Hold the chisel with your thumb on the outside. It
feels awkward at first, but prevents accidentally striking your thumb
with the hammer.
Start carving by cutting parallel rows about an
inch apart in the stone, creating ridges and grooves. Hold the chisel
at an angle that just bites into the stone, but not so steeply that it
will bury the tool. Try not to direct the chisel too deeply into the
stone, which will result in pulverizing the stone directly under the
point and producing a white blemish, or 'stone bruise.' These white
marks require a lot of additional work to remove.
Now go back over the same area with a cross-hatch
pattern of cuts to knock off the ridges of the first cuts. Place the
point so it catches under the ridge and the force pops the chip off.
Using this technique, begin defining the geometric planes of the large forms.
Work all areas of the sculpture simultaneously so
that the entire carving is always at the same stage of completion. In
this manner you can make more accurate visual judgments about
proceeding.
All of the hand-carving chisel shapes, the point, tooth, flat, and rondel, are also made to work with pneumatic hammers.
The pneumatic hammer's multiple-strokes-per-second
saves time and reduces some of the physical work of carving. Its smooth
action can cut a more flowing line through the softer stones.
The pneumatic hammer's rapid fire action, when
used with bushing chisels (4 point, 9 point, and cup chisel), make it a
very effective tool for shaping the harder stones like granite.
Pneumatic hammers come in different size from the
large 1 1/4" hammer for roughing out, to the 1/2", or smaller, for fine
detail work. The air pressure to the tool can also be increased for
more power or reduced for finer control.
Defining the Forms:
Once the large forms have been established with
the point chisel, begin refining them with a tooth chisel. The point
chisel has left a rough texture of grooves and ridges which can be
smoothed down with the tooth chisel.
The tooth chisel closely follows the contours of
the forms. Hold the chisel at about a 45 degree angle. A higher angle
only bruises the stone; a lower angle just skips over the surface. As
with the point, try to catch the tool under a ridge of stone to pop it
off.
A flat chisel is now used on flat or convex forms
to remove the texture left by the tooth chisel. Use the curved edge of
the rondel to clean out concave shapes.
During this cleaning up stage, you will discover
if you have bruised the stone and need to do extra work to remove the
white marks.
Finishing:
On the softer stones, rasps and rifflers are used
for the final smoothing and shaping of the carving. The coarse teeth of
a cabinet maker's rasp or round rasp, when used in long sweeping
strokes, produces graceful flowing forms.
On harder stones, a flat chisel is used to remove the ridges left by the tooth chisel.
The 9 point bushing chisel can be used on granite
to smooth the surface. A diamond cup wheel on a mini grinder will
remove the rough surface left by the bushing tools.
The smaller rifflers with their varied shapes can
get into small areas or complex shapes. On the softer stones, much of
the detail carving can be done with rifflers.
Final smoothing is done with wet/dry silicon carbide sand paper.
Polishing:
Polishing brings out the beautiful color and
pattern of a stone. With the softer stones, continue hand sanding with
the wet/dry sand paper under running water. Work through the grits (by
roughly doubling the number of the last grit) from 150 grit to your
desired degree of polish (somewhere between 600 to 3,000 grit).
On the harder stones, I use a pneumatic grinder
with a center water feed and diamond pads in an assortment of grits
from 40 to 3,000.
After you are finished thoroughly going over the
piece with a particular grit, let the stone dry. Check to see if there
are any scratches or other imperfections that were not removed by the
last grit. Mark the blemishes with a colored pencil and go over the
area again with the last grit until all the blemishes are removed
before proceeding to the next finer grit.
If you have gone through all the grits, but did
not stop and dry the stone to check for scratches, at the end you may
be shocked to find scratches left in the otherwise beautiful finish.
You have to start all over again from the beginning.
