A Charrette and a Plinth Block

The Charrette

This week the design for the Jacobean fireplace surround underwent a few final revisions regarding details. Two versions, each representing one half of the surround were presented full scale as a charrette. The one on the right was universally decided upon as having better proportions and more amenable to carving in limestone. At full scale, it is evident this is a large fireplace surround and a sizeable project for two students to take on for a semester.

Templates

Knowing what we are going to do allows the work to begin in earnest. The approved conceptual drawing is drafted unto heavy duty card stock and cut out for use as templates.






Carving a Plinth Block

Rough cut block

Best to start off with something easy. The plinth block provides a good way to warm up with a simple geometric form. After locating an appropriately sized leftover block in the yard, I cut it first in two using a mechanical grinder, as well as some additional waste. To the right is the raw block that has only two flat, parallel sides.

Establishing the lines

Using a combination square, a tungsten carbide tipped scribe and a 6H pencil, lines are used to delineate an orthotope (3 dimenstional rectangle) in successive steps. Tungsten carbide is about twice as hard as steel and is used as tips for many of the carving tools. Limestone has a relatively coarse grain. Without a hard lead, we would go through pencils rather quickly.

Pitch and Hammer

Once you have established a trustworthy line the first step is pitching. The "pitch" is a heavy chisel with an outwardly angled chamfered edge, designed to remove copious quantities of stone with a heavy blow. That blow is delivered with a steel hammer that transfers maximum impact into the pitch.

1/2" Chisel and Mallet

The next step that is repeated again and again is to "protect the line". This is done with the 1/2" chisel, an ideal size for controlled line working. By carving above the line in this way there is protection from heavier strikes creating fractures that reach the edge of the stone. Stone will almost always consistently fracture at the point of least resistance. You'll notice many of the tools are struck with a nylon mallet that absorbs much of the impact, offering greater control.

Punch and Hammer

The other "power" tool used to remove large quantities of material at a time is the "punch". Whereas the pitch has a flat surface and removes material from the edge, the punch digs in and removes stone directly from the face. Like the pitch, a steel hammer is used with the punch to transfer maximum force. This is done in rows so as to provide an unrestricted side to fracture towards.

Claw and Mallet

Once the surface is roughly evened out, a series of tools are used to approach the line. The first of these is often the "claw".  The heavy impact is distributed across a row of "teeth" and further softened by the use of a mallet. Claws are generally considered medium impact tools. The texture they create can be intentional and a finish unto itself.

Bolster and Mallet

A broad 2" chisel, the "bolster" is the tool used for the fine removal of material approaching and eventually reaching the finish surface. The bolster was the bane of my existence last year. Stone carving like a lot of craft skills require practice to "dial in", to feel the connection between yourself, the material and the tools. Almost like magic, it has clicked for me recently and I feel totally comfortable with the bolster.

Applying the Template

With my dimensionally correct orthotope completed I'm ready to apply my template. The profile of this plinth is simply a rectangle cut by a chamfer. The next few images show the template applied, a progress photo and the final result:

Progress on the Chamfer

The completed Plinth Block

Contributed by Patrick Webb