Roger Weller, geology instructor
Leticia L. Basurto
Cutting and polishing a Raw Gemstone
Where did gem cutting get its start? In prehistoric times 70,000 BCE man banged and hammered away with his tools of stone, rubbing one stone against another, polishing the stone by using sand, also man chiseled and carved out symbols and primitive writings on hard rock and cave walls. In doing so, man learned the great secret that some stones are harder than others and they are capable of inflicting scratches on other less hard stones.
This is how drilling and butting became possible. Drilling was the first of the lapidary arts, and it shows itself as far back as 1,000,000 years ago. In these times people learned that rocks could be broken or fractured. Butting was the shaping of a gem through rubbing one gem against another harder mineral type
At one time man compared the smooth polished effect from the stones that came out of a river and a stream. Man concluded that something was bringing a smooth and polishing effect to the stones in these streams. It was believed that other particles in the river working to complement the action of the constantly running water.
By 3,000 BC man had developed lapidary skills to such a level that cylinders made of serpentine, were commonly used. Before Christ, lapidaries had pretty much conquered the challenges of sawing, chipping, drilling, and faceting. The work was crude but there is much work that is still with us today.
Photo is from “The History of Lapidary”
Many diamond cutters used a small box beneath their manipulations, as in the picture on page one. This was called a butters box to catch the rubbings or diamond dust, whose grit was so tiny it was later used in the polishing process. The technique was used until more refined techniques were introduced.
In the 1400’s was when the breakthroughs went into full swing. Louis de Berquen, of Bruges, Flanders, was acknowledged as the Father of Modern Diamond Cutting, in 1476. His introduction of absolute symmetry, improvements in the polishing process and the development of the pendeloque shape. He developed the horizontally mounted metal grinding wheel (skeif).
He covered the metal wheel with diamond dust suspended in oil. The oil, kept the diamond particles on the rotating wheel rather than allow centrifugal force to sling them away. This led to great advances in polishing technology and control of the stones that had been cut.
The Bead and Cabochon known as “Glyptic” was the first gemstone cuts used by man. It was the first choice for jewelry making and ornamentation. These stones were shaped by rubbing them with other stones and polished by using sand as an abrasive. These cuts go back to the 7th millennium. The examples below are some of the early Roman gemstone cuts with several variations of cameo and intaglio.
Photo is from “Lapidary History Early Gemstone Cuts”
A cabochon is a shape that is simply rounded as opposed to a faceted cut. In the 1400’s, gem cutters were limited to the cabochon, due to the limited technology available. A cabochon is used to describe a cut of a gemstone that is not facetted. When cutting a cabochon, the small amount of light that is able to pass through the stone is due primarily to its crystalline structure and optical qualities. Cutting a stone cabochon is usually applicable to opaque gems, although transparent semi-precious gemstone can also be cut cabochon cut. Below are some more examples of cabochon cuts. Cabochon cutting, or cabbing, is often done by simply holding the stone with the fingers of both hands. This allows the twirling of the stone to form smooth curves and avoid flat areas during grinding, sanding, and polishing. A typical cabbing machine holds several wheels representing different series of diamond or silicon carbide grit (80, 220, 280, 600, 1200, 14,000) turned by an arbor and motor, and a water supply that provides a
coolant/lubricant to wash away debris and keep the stone from overheating as it is ground and sanded on progressively finer wheels.
Photo is from “Lapidary History Early Gemstone Cuts
Other types of cuts are facetted cuts, which are usually done on transparent stones. Facetted gemstone and diamond were introduced in European jewelry during the late 13th and 14th centuries. Flat facets usually in a high symmetrical pattern, are cut and polished over the entire surface of a stone.
A stone that is faceted, is dopped, usually with adhesive wax, on a metal dopstick to control the positioning of the cutting angle. The facets are then ground, sanded, and polished on a rotating lap, while rotating water acts as a coolant /lubricant. When one side top or bottom of the stone is finished, the other side of the stone is transferred to a dopstick on the opposite side. In recent years faceters have acquired techniques such as concave facets, grooves, and combinations of faceting and cabbing to produce new forms in faceted stones. Below are some photos of the construction of the gem cutting machine. Next is the model of the gem cutting machine and the image of the diamond cutters engraving using his books in 1694 and using a foot powered cutting wheel.
Photo is from “Gem Cutting &The History of Faceting Gemstones”
CUTTING AND POLISHING
The steps to cutting and polishing a stone are:
Marking: A rough stone is always marked to determine the direction of the grain or cleavage. The natural shape of the stone will be important in deciding how to cut the stone.
Cleaving: When a stone is struck along its grains to split it.
Sawing: The stone is cut closer to the shape of the finished cut without any facets. When sawing the stone there is water or oil moving at all times to prevent overheating. The sawing can also give stone unwanted fractures. Sawing is when all the unwanted material is removed from the stone to get closer to desired cut. The next page is an image of a saw cutting a raw stone close the shape wanted.
Grinding: The stone is on a dopstick or held with the fingers to move around to each wheel. Each wheel has a different grit ranging from 80, 220, 280, 600 grit. This process is for shaping and sanding of the stone. This machine also needs coolant to prevent overheating.
Sanding: Sanding the stone is the same process as grinding, but with finer abrasives
1,200 and 14,000 grit. This step is to remove deep scratches.
Lapping: Lapping is similar to grinding and sanding. The process is usually done on a
rotating or vibrating flat disk known as a lap, this is to create flat surfaces on a stone. Laps are usually made of cast iron, steel, or a copper-bronze alloy.
Polishing: Polishing the stone is done on a felt, leather, cloth, cork, wood, tin, tin-lead or lucite laps. The wheel is wet with a polishing agent such as a metal oxides - aluminum oxide (alumina), cerium oxide, tin oxide, chromium oxide, ferric oxide (jeweler's rouge), or silicon
dioxide (tripoli). This is the last procedure and it is to remove any rough marks left by coarser grits.
I marked and cut my stone closer I sanded off parts of I heated the stone, put wax,
to finished shape. I used a tile saw raw stone remaining. placed it on dop stick.
in place of a saw for cutting This is a rough
Stone is on dop stick ready to be Final step is to polish, I used cerium
sanded and shaped from wheel oxide on leather wheel, needs to be
to wheel (80, 220, 280, 600, wet to remove any rough marks.
1000, 14000) grits. This is a