10 Measuring devices
The various devices used to measure the stone allow the stone to be visualised, and adapted to fit its eventual location.
The straight edge is not only for drawing straight lines, it also used by the mason to test for flatness— the most useful straight edges have a beveled edge, because the narrow edge makes it easier to spot any inaccuracy.
The blade can be adjusted and locked into virtually any angle. Once the shape is made, this tool can be used repeatedly to test the bevel on several carved stones for alignment and accuracy.
A tool that confirms or corrects a right angle. With an L-square a block can be squared up as an aslar or to prepare the stone for easier use of templates.
The Spirit Level and Plumb Line
Both the level and plumb line use natural forces to determine the horizontal and vertical axes: the surface water flattens, and the gravitational pull on a suspended weight will make it hang straight. No doubt the Cartesian co-ordinates were inspired by these two principles.
Templates involve a specific thinking in which two-dimensional silhouettes are projected in order to create three-dimensional forms. Multiple templates require skills of visualisation and translation as the carver moves the form into deeper space.
Calipers can be used with great skill to measure or divide a stone into equal parts. Calipers are also used to enlarge a sculpture from a maquette or on occasion to reduce it. A ‘master line’ is established on a maquette to serve as a constant reference point for all subsequent measurement. An equivalent line is established on or in the stone that is going to be carved.
The Pointing Machine
The pointing machine was invented in France in the mid 18th century although it is likely that the Greeks had a similar devise. For ancient Greeks stone had no intrinsic value. It was used as a secondary material and for copies. We know the existence of bronze sculptures long ago destroyed only because the stone copies that were made still exist.
The introduction of the pointing machine changed the nature of stone work in many respects. By the late 19th century stone once again became an imitative material. Carvers with less experience or innate skill could produce reasonable results.
The pointing machine is a three dimensional pantograph able to reproduce points proportional between smaller and larger models. In its simplest form the pointing machine was a movable cross-shaped armature with three sharp points – two on the cross beam and one on the vertical with a hook to hang over the top of a block of stone.
To keep the work accurate and resist wear on the maquette, three places are prepared with small metal plates – usually indented to precisely anchor the contraption.
In its simplest form the carving is based on a full size model and the measurements are transferred one to one. Enlarging and reducing require slightly different tools. Different methods can be used but the principle is to enlarge or reduce each measurement proportionally.
Like all tools, the pointing machine embodies a particular principle of action. Establishing strategic points into which the work nestles is an application that can be applied elsewhere and in other approaches to working, such as drawing, surveying or carpentry. The principle of certain points in one place that correspond to points somewhere else is also one of the ideas of metaphysics. In the Pointing Machine, speculation becomes practical.
The pointing machine is used at least three times in the completion of a sculpture. The three stages can be summarised this way:
Stage one: Pre-pointing or primary blocking
Holes are drilled or the marble carved away to the depths indicated. To allow for a margin of error, the rough form is established approximately 3 cm (or 1 inch) larger than the finished sculpture. The first points of reference are at the highest relief points. Points have to be placed as needed, but for a 1,50 m — or 6 foot — block of marble the points might be about 15 cm —or 6 inches— apart.
Stage two: The pointing itself
The entire sculpture is now brought within about 1 cm — a third of an inch— of the finished form. The proximity of the points depends on the detail of the areas being carved. Something like an ear or delicate foliage might need many points, a fairly uniform area needs fewer.
Stage three: Details
The work is finished and polished. The pointing machine can be also be used at this stage, especially for extremely delicate areas. Parts of a face, for instance, might need many points quite close together.
The pointing machine uses a principle that is also at the heart of contemporary animation techniques, specifically motion capture. In motion capture specific facial movement markers are established and then tracked. There are apparently 70 poses of the human face that can be mapped and used in surface capture. The face can also be carved up into smaller components, a kind of map that is composed of hundreds of composite polygons looking as if the surface is composed of a net that adjusts itself to changing positions. Once mapped, transposing data onto another mode is relatively simple. The use of this technology is particularly helpful for research into dance and animation,
Digital stone carving is another variation of this principle. Like the simple pointing machine, points are established and these points then guide the carving. The apparently modern is in reality only an old technique.
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