Thursday, February 09, 2012

The Principle of Stone Cutting

Steve Manuel demonstrating the inscribing of a line on stone.

Stone masonry is a skill that I was keen to learn, so when Heather Newton agreed to allow me into the workshop for some instruction, I was thrilled.  Today the conversion of rough quarry stone into wrought stonework is done by machinery, but that was not true when the cathedrals were erected.  As such it is important to understand the "ontology of stone cutting" if a thorough understanding of the cathedrals is to be articulated.

I met Steve Manuel the first day in the work room, and it was mostly under his instruction that the skills were demonstrated and practised.  Even though I learned only the very basic techniques, it would seem that the foundation is set for further technique development.  Working with the stone directly gives an intimate knowledge of the material than would otherwise be possible.  Chisel and mallet on stone cannot be replaced.

While I did not learn how to split stone at the quarry, it seems reasonable that I will be able to do so in the future given my skill level thus far.  I was able to cut stone using a tungsten saw blade, so I am not a complete novice of splitting stone.  While the stone I was using was "soft", I would not want to saw it by hand for long periods.  The work was not the easiest, and I would soon tire of sawing stone.

The technique of stone cutting with a chisel requires working away from the corners.
Converting a rough stone into a stone that fits into a building requires chiselling on the surface of operation.  My first task was to remove one half inch of stone from the surface of operation, and render the surface as smooth as possible without and twists or deformations, so that any surface may be squared true from it.  A guiding line on each side of the stone is drawn using a "scribe", and the groove created by the scribe is filled with graphite from a pencil to render it more visible to the eye.  Beginning with the corners of the stone, and a "drafting chisel", a marginal draft is created along the longest edge.  Careful attention must be paid to the inscribed line, and the drafting chisel must not remove too much stone.
The marginal draft created by the drafting chisel.
Cutting a corner into the stone requires the chisel to cut into the stone, rather than away.  The chisel cutting edge should travel towards the mass of the stone when cutting a corner, rather than away because the stone will gouge out other wise.  After the first two corners are cut, then the draft between the corners is cut, then a visual inspection is required.  The marginal draft is checked for straightness using a straight edge, and visually inspecting the contact between the straight edge and the stone.  It is evident where the high and low points are, and the extra stone should be carefully removed using the drafting chisel.
The marginal draft being checked for straightness.

After the initial marginal draft is completed, another corner should be cut.  Following the corner cut another marginal draft joins the two corners, and the entire procedure is repeated until the entire surface of operation is enclosed by a marginal draft.  All marginal drafts should be checked with a straight edge.
A marginal draft encloses the entire surface of operation.
 To prevent surface twisting it is important to sight in the marginal drafts using two straight edges, and visually confirming they are parallel whilst resting on the marginal draft surfaces.  The chisels can be a convenient item for holding the straight edge in place.
Sighting through the marginal drafts with straight edges held in place by a chisel.

To remove the superfluous stone enclosed by the marginal drafts, a series of furrows are worked through using a "punch".  The extra stone is knocked off, and careful attention is required so as to not drift below the final required surface.  Each punched furrow should be checked with a straight edge, and should be level before continuing.
The furrows created by the punch.

The surface is then "clawed" in parallel drafts using a mallet and claw chisel.  These drafts should be worked in the same direction as the furrows, and tested by applying the straight edge.  A series of drafts is now worked with a mallet and boaster.  These should be worked parallel to the initial marginal draft, and each one tested and worked until it is correct before the next draft is boasted.  Each draft is a guide for the working of the next, and so on across the surface.  The straight edge should be applied diagonally across the surface.  If the stone is round in one direction and hollow in  another direction, it is proof the the surface is twisting.  It is then necessary to rework the marginal drafts, and repeat the processes.
A draft begun using the claw chisel.

A draft using the bolster.

After the surface of operation has been worked true, the templates or moulds should be applied to the stone, the outline of the mould being scribed or marked on the surface by means of a scriber, after which pencil may be used to define the lines clearly.  The various surfaces may be worked square from the surface of operation, in stages.
A scribe and acrylic template sit atop the tone with profile inscribed.
 The procedure did not vary during the various stages of cutting a moulding profile.  First the corners are cut, then a draft between them using a drafting chisel, followed by the claw chisel, followed by the bolster.
A corner cut into the stone before a draft was cut to reveal the moulding lip.
 After the moulding lip was cut with the bolster and mallet, the large amounts of excess stone was removed using a pitching tool.  It is very good at splitting the stone and sending large pieces into the air.  It can be a precarious tool if not used properly as large unwanted cracks could develop.  Steve was quite confident, but I was not so much.  I didn't want the work completed thus far to be ruined.
The pitching tool which easily removes large quantities of stone.
 The corners are again cut using a drafting chisel, but are joined by carefully following the curved moulding profile.  Again this is followed by furrowing through the excess stone with a punch, then a clawed chisel, then a boaster.
The drafting chisel was used to cut along the curved moulding profile.

The curved moulding profile with marginal drafts defining the edge of the moulding curve.

A claw chisel removing excess tone after the punch tool was used.
 After the curve was finished I wanted to cut the stone in half because it was very heavy.  As I wanted to keep it, this was the best option.  The experience of cutting the stone was desirable as I was not able to quarry and rough cut the stone from the beginning.  If I had to cut many stones in the future a machine would be very desirable.
A tungsten saw blade used to cut the stone.

The finished stone.
What did I learn from this exercise?

Apart from the meditative and enjoyable nature of the work, the importance of progression from one step to the next is readily apparent.  Each step should be completed with full attention before continuing onto the next.  If the mind drifts, then mistakes are made.  The skill and method of working emphasises a series of steps, and each step depends greatly upon the step prior.  Stone masonry is an unfolding of sequences as determined by the stone itself.