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Here Comes Treble: Lapidary – Art From Tribology

"Cutting, polishing and shaping stones is an ancient art, known as lapidary. Lapidarists, sometimes known as lapidaries, are not only artists, but are experienced Tribologists, applying their knowledge of friction, wear, materials and lubrication to create exquisite gems from raw rock,'' writes Isabel Bradley.

Since prehistoric times, people have adorned themselves with all manner of decorative items, stringing feathers and shells, bones and stones onto necklaces and sewing them onto clothing. They placed them around caves, shelters and houses, either for purely decorative purposes, as protection from illness and evil spirits or to encourage spiritual well-being.

Lapidarists were among the first artisans. During the stone-age, which lasted about 3.4 million years, drawing to an end between about 4500 BC and 2000 BC, tools were chipped and flaked, or knapped out of rough flint, chert and obsidian. Such tools were used for domestic chores such as hammering, chopping, cutting, scraping and building. Weapons such as spears, arrow-heads and clubs, were made for killing animals for food, or for defence.

Cutting, polishing and shaping stones is an ancient art, known as lapidary. Lapidarists, sometimes known as lapidaries, are not only artists, but are experienced Tribologists, applying their knowledge of friction, wear, materials and lubrication to create exquisite gems from raw rock.

Over the centuries, ‘rock-hounds’ improved the methods of smoothing and shaping stone. Although the discovery of bronze ended the necessity for stone weapons and tools, shaped and polished gems were inset into metal bracelets, rings, brooches, necklaces, sword-hilts and handles, daggers and shields. Gemstones became items of value and beauty.
Lapidarists use three main techniques to bring out the shine in stones: tumbling, cabochon-making (cabbing) and faceting.
Tumbling is possibly the simplest form of smoothing and polishing stones, and historically dates back to Ancient Egypt, where slaves would carefully chip basic shapes from stone and then tumble them back and forth in troughs filled with sand and water. The friction thus created would gradually wear the edges off the stones and smooth and polish them. In India, lapidarists used tumbling bags made of goat-skin into which they placed the pre-shaped stones with a mixture of finely-ground rock and water. They then rolled the bags on the ground, gradually smoothing and polishing the stones inside. Use was made of ‘teeter-totter’ boards on which jars filled with stones or beads, some form of abrasive and lubricated with water, were rolled back and forth.

These early methods were very labour-intensive, taking many months before stones reached an acceptable standard for use in jewellery and other forms of decoration.

In the mid-20th Century, tumbling of semi-precious gem-stones became popular as a hobby. People began tumbling their rock ‘blanks’ in barrels made of paint cans, a noisy and inefficient process. Eventually, tumblers were manufactured specifically for the purpose. Modern tumblers are run by small, electric motors and are often made of, or lined with, rubber to enable a quieter process.

Today, lapidarists use a variety of abrasive materials other than just sand or ground rock. Rough grades of silicon carbide are used for initial shaping of stones, removing corners and edges. The stones are processed through a series of perhaps a week’s tumbling, followed by a thorough cleaning of the barrel and washing the rough grit off the stones, before tumbling again with increasingly fine grades of grit until, for the final polishing, cerium oxide powder is used in the tumbler. Stones polished by tumbling make colourful displays in bowls, can be incorporated into beautiful pieces of costume jewellery, or used in any position where adornment is required.

Creating a cabochon is a very different technique from tumbling. A cabochon usually has a flat base and a rounded, highly-polished dome, though it can also be made completely spherical. Cabochons are frequently shaped as an ellipse, and are mostly used for showing opaque stones to their best advantage.

First, a slab-saw is used to cut a rough ‘slab’ or basic shape from the rock. The required pattern is then stencilled onto the rough slab using a template, making use of interesting shapes, patterns and colours within the stone. Excess material is cut away with a small, diamond-bladed trim saw, creating a ‘preform’. The preform is attached, with hard wax, to a ‘dop-stick’, or wooden dowel. Using a diamond-impregnated grinding wheel, the stone is gradually ground to the exact shape of the template line. The edges are then bevelled, or smoothed and rounded, using increasingly finer grades of diamond-impregnated laps, starting at 170 grit and ending with 1200 grit, ensuring that at each change of grade, the machine is properly flushed out, the laps are cleaned and the developing cabochon is washed clean and dried so that no debris remains. The final stage is polishing the dome of the stone to a smooth and silky or shiny finish, with the aid of cerium oxide on a felt lap.

Faceting stones is, once again, a more complex process. This process is used on harder, crystalline stones that are transparent or translucent, such as tourmaline, garnets, citrines, amethysts, rubies, emeralds, sapphires, and of course, diamonds, though diamonds require specialised skills.
Faceting is cutting ‘small faces’ in the stone, using reflection and refraction of light to bring out the colours and shapes. This method of cutting and polishing gems began in Bruges in the mid-1400s. Repeating geometric forms are used as a basis for all styles of faceting, which are becoming increasingly complex.
A typical faceting machine consists of a flat, rotating table holding an abrasive disk; an electric motor to turn the table, an arm and mast to hold the gem against the disk, a bottle to drip water on the disk and positioning controls on the arm and mast.

Once again, laps of varying grits are used to grind, cut and polish the stones. The lapidarist must orient the rough crystal so that its best colour will be revealed and enhanced by the facets. Using a grinding wheel, the ‘rough’ is sized and shaped by hand. The resulting stone is shapeless and frosted in appearance, and is called a preform. It has a relatively large flat spot, by which the preform is attached to a dop stick made of metal. The dop stick slots into the arm of the faceting machine. Sometimes dopping wax is used, though if the particular stone being faceted is sensitive to heat, glues can be used in place of the wax. In modern machines, calculations of the angle and position of each facet is computer-assisted.
The lapidarist performs a series of first coarse-cutting the lower or ‘pavilion’ facets then returning to each and polishing it to a highly-reflective finish, taking care that all facets meet with precision. The partially-faceted gem is then removed from the dop-stick and re-positioned on a different dop-stick, to allow work on the crown, or upper facets. Taking care that the new dop-stick is positioned to ensure symmetry, the lapidarist cuts and polishes the crown facets, where the initial flat spot magically becomes the ‘table facet’, large and horizontal, that ‘acts as a window into the interior of the gem’.

Lubrication of machines and blades, which are often water-cooled, is essential. Lubricants and additives are available in many forms: in both powder and liquid, they are biodegradable, hypo-allergenic, synthetic, petroleum-based, refined mineral-oils, silicone-based, or non-toxic food-grade mineral oils. These compounds are variously harmless to skin, contain wetting agents and rust inhibitors, are non-flammable, they eliminate surface tension and prevent hydroplaning and suppress the undesirable mists of oil coolants.

A successful lapidarist has an innate ability to recognise the potential beauty in a rough stone or crystal. He then needs to acquire a thorough knowledge of the qualities of the stones, the operational and maintenance aspects of the machines he will use, an understanding of the effects of friction and the ability to control it. Time and experience will bring him the skills required to create gems that will be universally admired and desired.

Lapidary is Tribology in Action from start to finish.

Until next time…. ‘here comes Treble!’


















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6 November 2012 by Isabel Bradley


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