Posted September 24th, 2008 by admin
The influence of time and weather have almost certainly dulled or marked their surfaces, and it is the work of the lapidary to produce a beautiful stone from the piece of unattractive rough material which he is handed. Badly flawed pieces are not usually cut; cleavage, optical properties, and hardness must be considered, and the cutting of stones into definite shapes with definite proportions calls for considerable skill and experience.
Abrasives,” very hard, substances used in the working of gem materials in order to grind away .or polish rough surfaces, are a most important factor in lapidary work. In recent years, several artificial abrasives have been produced, many of which are far superior to natural substances which have long been used. Diamond, however, still remains the hardest substance known, and carbonado and boart, two types of this stone which are used almost exclusively as high grade abrasives, are of great importance in many industries outside of gem cutting.
Corundum, emery, and garnet are also used, as well as the artificial carborundum. Other abrasives are artificial corundum and boron carbide. Corundum is now made by fusing bauxite in the electric furnace, and it is marketed in various forms under different trade names. Boron carbide, or Norbide, is made from a mixture of borax and coke, and it is considerably harder than either corundum or carborundum.
Posted September 24th, 2008 by admin
We usually see gem stones set in some form of jewelry when they are cut and polished. In order to present them in this form so that their natural beauty is brought out to the best advantage, various work has to be performed by the lapidary, and cutting, polishing, and drilling are all highly skilled crafts. The final use of the finished stone is the concern of the manufacturing jeweler or the mounter.
When found, precious stones are almost always in forms unsuitable for immediate use. Their shapes are usually irregular and their surfaces dull; they may be broken or flawed, or associated with matrix which has to be cut away. The final shape should exclude all large and obvious flaws and at the same time exhibit the fundamental color and brilliance to the best advantage. As the value of all stones depends largely on size, or weight, no good material must be wasted. The broken crystals, slabs, or pieces must be individually studied before they are shaped and fashioned.
Posted June 2nd, 2008 by admin
The stone cutting industry has been carried on here for a great length of time. The Romans knew of the agates which were to be found in the neighborhood, and they took the rough stones to Italy for cutting. In course of time, Roman craftsmen settled locally and carried on the grinding and cutting of these stones in order to save their transport to Italy. With the fall of the Roman empire, the invaders withdrew, and the craft was almost forgotten. It was not until the Fifteenth Century that stone quarrying in the lands of the Counts of Oberstein was mentioned.
Methods of communication to neighboring towns were gradually improved, and the finished stones were taken to the trade fairs at Frankfurt-on-Main and Leipzig, where they soon gained an international reputation. In the early years of the Nineteenth Century, the processes of staining agates were exploited, and continual new sources of rough stones being discovered, the industry increased enormously. Fashion played a great part in the demand for certain stones at different times, the local merchants no doubt having a great influence in directing fashion as new fields were discovered. The engraving on stones as well as cameo cutting were once very fashionable, and some fine work was executed. The Germans learned much of this craft from the French, with whom they came in contact during the Franco-Prussian war of 1870. There has been little demand for engraved stones in recent years, and the number of skilled engravers is now small. Much more emphasis is placed on the mass production of faceted and cabochon stones, which are normally turned out in huge quantities in definite sizes for the American and other markets.
Posted March 16th, 2008 by admin
For the final polishing, the stone is soldered firmly into a holder, a hollow cup called a “dop,” and then held against a fast rotating mill or lap of soft iron. The dop is usually a hemispherical bronze cup on a copper stem, and the stone is held in the dop and almost embedded in it by melting lead and tin in the proportions of three to one respectively. Mechanical dops Which hold the stone by screw adjustments are now usually used. Lines across the surfaces and edges of cleavage planes are eradicated by the disc moving across the grain; otherwise polishing follows the grain.
The dop is placed in a flexible copper arm reaching over the polishing lap, and additional lead weights are placed on the arm to increase the pressure when so required.
Since the laps are rotated at high speeds, they quickly become hot and the oil in the paste soon dries, leaving powdered diamond on the metal. The dop is occasionally immersed in water, and inclined at different angles for the different facets. The stone must be re-set in the dop for each new facet, which is quite a lengthy process requiring some skill. Adjustments are made by the eye only. If the stone contains flaws, a dry disc is used for polishing to obviate the risk of the dirty paste creeping into the cracks and thus discoloring the stone. The polished cut stone is finally cleaned by boiling in a solution of strong nitric or sulphuric acid to free it from oil and grease. In its process of being fashioned from the rough stone to the finished gem, it has lost from one-half to two-thirds of its original weight.
