A cabochon is a gemstone, shaped and polished as opposed to faceted. The resulting form is a convex obverse with a flat reverse. Cutting en cabochon is applied to opaque gems, while faceting is applied to transparent stones. Hardness is taken into account as softer gemstones with a hardness lower than 7 on the Mohs hardness scale are scratched by silicon dioxide in dust and grit; this would make translucent gems unattractive—instead they are polished as cabochons, making the scratches less evident. In the case of asteriated stones such as star sapphires and chatoyant stones such as cat's eye chrysoberyl, a domed cabochon cut is used to show the star or eye, which would not be visible in a faceted cut; the usual shape for cutting cabochons is an ellipse. This is because the eye is less sensitive to small asymmetries in an ellipse, as opposed to a uniformly round shape, such as a circle, because the elliptical shape, combined with the dome, is attractive. An exception is cabochons on some watches' crowns.
The procedure is to cut a slab of the rough rock with a slab saw, next to stencil a shape from a template. The slab is trimmed near the marked line using a diamond blade saw—called a trim saw. Diamond impregnated. Most lapidary workshops and production facilities have moved away from silicon carbide to diamond grinding wheels or flat lap disks. Once the piece is trimmed it can be "dopped" or completed by hand. "Dopping" is done by adhering the stone with hard wax onto a length of wooden dowel called a "dop stick". The piece is ground to the template line, the back edges may be bevelled, the top is sanded and polished to a uniform dome. Cabochon Making 101
A coolant is a substance liquid or gas, used to reduce or regulate the temperature of a system. An ideal coolant has high thermal capacity, low viscosity, is low-cost, non-toxic, chemically inert and neither causes nor promotes corrosion of the cooling system; some applications require the coolant to be an electrical insulator. While the term "coolant" is used in automotive and HVAC applications, in industrial processing heat transfer fluid is one technical term more used in high temperature as well as low temperature manufacturing applications; the term covers cutting fluids. Industrial cutting fluid has broadly classified as neat cutting fluid. Water soluble coolant is oil in water emulsion, it has varying oil content from nil oil. The coolant can either keep its phase and stay liquid or gaseous, or can undergo a phase transition, with the latent heat adding to the cooling efficiency; the latter, when used to achieve below-ambient temperature, is more known as refrigerant. Air is a common form of a coolant.
Air cooling uses either convective airflow. Hydrogen is used as a high-performance gaseous coolant, its thermal conductivity is higher than all other gases, it has high specific heat capacity, low density and therefore low viscosity, an advantage for rotary machines susceptible to windage losses. Hydrogen-cooled turbogenerators are the most common electrical generators in large power plants. Inert gases are used as coolants in gas-cooled nuclear reactors. Helium has a low tendency to become radioactive. Carbon dioxide is used in AGR reactors. Sulfur hexafluoride is used for insulating of some high-voltage power systems. Steam can be used where high specific heat capacity is required in gaseous form and the corrosive properties of hot water are accounted for; some coolants are used in both liquid and gas form in the same circuit, taking advantage of the high specific latent heat of boiling/condensing phase change, the enthalpy of vaporization, in addition to the fluid's non-phase-change heat capacity.
Refrigerants are coolants used for reaching low temperatures by undergoing phase change between liquid and gas. Halomethanes were used, most R-12 and R-22 with liquified propane or other haloalkanes like R-134a. Anhydrous ammonia is used in large commercial systems, sulfur dioxide was used in early mechanical refrigerators. Carbon dioxide is used as a working fluid in climate control systems for cars, residential air conditioning, commercial refrigeration, vending machines. Many otherwise excellent refrigerants are phased out for environmental reasons. Heat pipes are a special application of refrigerants. Water is sometimes employed e.g. in boiling water reactors. The phase change effect can be detrimental. Phase-change materials use the other phase transition between liquid. Liquid gases may fall here, or into refrigerants, as their temperature is maintained by evaporation. Liquid nitrogen is the best known example encountered in laboratories; the phase change may not occur at the cooled interface, but on the surface of the liquid, to where the heat is transferred by convective or forced flow.
Water is the most common coolant. Its high heat capacity and low cost makes it a suitable heat-transfer medium, it is used with additives, like corrosion inhibitors and antifreeze. Antifreeze, a solution of a suitable organic chemical in water, is used when the water-based coolant has to withstand temperatures below 0 °C, or when its boiling point has to be raised. Betaine is a similar coolant, with the exception that it is made from pure plant juice, is therefore not toxic or difficult to dispose of ecologically. Pure deionized water, due to its low electrical conductivity, is used to cool some electrical equipment high-power transmitters and high-power vacuum tubes. Heavy water is a neutron moderator used in some nuclear reactors. Light water reactors, both boiling water and pressurised water reactors the most common type, use ordinary water; some designs, e.g. CANDU reactor, use both types. Polyalkylene glycol is used as high temperature, thermally stable heat transfer fluids exhibiting strong resistance to oxidation.
Modern PAGs can be non-toxic and non-hazardous. Cutting fluid is a coolant that serves as a lubricant for metal-shaping machine tools. Oils are used for applications where water is unsuitable. With higher boiling points than water, oils can be raised to higher temperatures without introducing high pressures within the container or loop system in question. Many oils have uses encompassing heat transfer, pressure transfer, sometimes fuel, or several such functions at once. Mineral oils serve as both lubricants in many mechanical gears; some vegetable oils, e.g. castor oil are used. Due to their high boiling points, mineral oils are used in portable electric radiator-style space heaters in residential applications, in closed-loop systems for industrial process heating and cooling. Mineral oil is used in submerged PC systems as it is non-conductive and therefore won
Hardstone carving is a general term in art history and archaeology for the artistic carving of predominantly semi-precious stones, such as jade, rock crystal, onyx, serpentine, or carnelian, for an object made in this way. The objects are small, the category overlaps with both jewellery and sculpture. Hardstone carving is sometimes referred to by the Italian term pietre dure. From the Neolithic period until about the 19th century such objects were among the most prized in a wide variety of cultures attributed special powers or religious significance, but today coverage in non-specialist art history tends to be relegated to a catch-all decorative arts or "minor arts" category; the types of objects carved have included those with ritual or religious purposes, engraved gems as signet rings and other kinds of seal, belt hooks and similar items and purely decorative objects. Hardstone carving falls under the general category of glyptic art, which covers small carvings and sculpture in all categories of stone.
The definition in this context of "hardstone" is unscientific and not rigid, but excludes "soft" stones such as soapstone and minerals such as alabaster, both used for carving, as well as typical stones for building and monumental sculpture, such as marble and other types of limestone, sandstone. These are not capable of a fine finish in small carvings, would wear in prolonged use. In other contexts, such as architecture, "hard stone" and "soft stone" have different meanings, referring to actual measured hardness using the Mohs scale of mineral hardness and other measures; some rocks used in architecture and monumental sculpture, such as granite, are at least as hard as the gemstones, others such as malachite are soft but counted as hardstones because of their rarity and fine colour. Any stone, used in jewellery is to count as a hardstone. Hard organic minerals such as amber and jet are included, as well as the mineraloid obsidian. Hardstones have to be drilled rather than worked with edged tools to achieve a fine finish.
Geologically speaking, most of the gemstones traditionally carved in the West are varieties of quartz, including: chalcedony, amethyst, onyx, heliotrope and quartz in its uncoloured and transparent form, known as rock crystal. The various materials called jade have been dominant in Mesoamerican carving. Stones used for buildings and large sculpture are not used for small objects such as vessels, although this does occur. For example, in the Uruk period of Sumerian culture heavy vases and ewers of sandstone and limestone have been found, but were not for common use, as the people of Uruk had well-developed pottery; the art is ancient, going back to the Indus Valley Civilization and beyond, major traditions include cylinder seals and other small carvings in the Ancient Near East, which were made in softer stones. Inlays of semi-precious stones were used for decoration or highlights in sculptures of other materials, for example statues had eyes inlaid with white shell and blue lapis lazuli or another stone.
Chinese jade carving begins with the carving of ritual objects, including blades for ji and dagger-axes never intended for use, the "Six Ritual Jades" including the bi and cong, which according to much literature represented heaven and earth respectively. These are found from the Neolithic Liangzhu culture onwards, blades from the 2nd millennium BCE Shang Dynasty on. Traditional Chinese culture attaches strong powers to jade; the Chinese and other cultures attributed specific properties for detecting and neutralizing poison to gemstones, a belief still alive in the European Renaissance, as shown by the works of Georgius Agricola, the "father of mineralogy". The English word "jade" derives from the Aztec belief that the mineral cured ailments of the kidneys and sides; the Han period saw the beginning of the tradition of fine decorative jade carving which has lasted until modern times, though the fine carving of other hardstones did not develop until the 17th century, appears to have been produced in different workshops and styles from those for jade.
In general whiteish nephrite jade was the most regarded in China until about 1800, when the deeper and brighter green of the best jadeite became more favoured. There are related Asian traditions of Korean jade carving, in Southeast Asia and, to a much lesser extent, Japan. Smallish Sassanian carvings are known for seals or jewellery. Egyptian carving of rock crystal into vessels appears in the late 10th century, disappears after about 1040. In 1062 the Cairo palace of the Fatimid Caliphate was looted by his mercenaries, the examples found in European treasuries, like the one illustrated, may have been acquired as the booty was dispersed; the rock crystal used in Egypt was traded from East Africa. Until it was thought that jade carving was introduced to the central Asian Islamic world in the Timurid period, but it is becoming clearer that archers' thumb rings, knife hilts, various other objects had been carved for centuries millennia before, though in limited numbers. Islamic jades and other carvings reached a particular peak in th
A diamond blade is a saw blade which has diamonds fixed on its edge for cutting hard or abrasive materials. There are many types of diamond blade, they have many uses, including cutting stone, asphalt, coal balls and ceramics in the construction industry. Diamond blades are available in different shapes: Circular diamond saw blades are the most used type of diamond blade. A diamond gang saw. Tens or hundreds of diamond gang saw blades are used together to saw raw stone blocks. A diamond band saw blade is a flexible closed steel band with diamonds fixed on one edge of the band. Diamond blades designed for specific uses include marble, concrete, asphalt and gem-cutting blades. General purpose blades are available. Blades using diamonds embedded in a metal coating of nickel electroplated onto a steel blade base, can be made to be thin—blades can be tens of micrometres thick, for use in precise cuttings. Vacuum brazed diamond saws are manufactured by brazing synthetic diamond particles to the outside edge of the circular saw blade in a vacuum brazing furnace.
All of the diamond particles are on the exterior cutting edge of the blade, with no metal-diamond mixture. Depending on the manufacturer's recommended blade application, vacuum brazed blades will cut a wide variety of material including concrete, steel, various irons, tile and glass. Finer synthetic diamond grits will reduce the chipping of tile and burring of steel and provide a smoother finish. Larger diamond grits will provide a higher cutting speed, but will be more to cause chipping, burring, or cracking. Fire departments require blades to be made with a large diamond grit, to tear through material quickly. An intermediate grit size is used by the production industry. Sintered metal-bonded diamond blades are the most common type of blade; these blades consist of a steel core and diamond segments, which are made by combining synthetic diamond crystals with metal powder and sintering them. The diamond segments are known as the "cutting teeth" of the blade; the steel core can vary in design. Some cores have spaces between segments to provide cooling and slurry removal, while others have a single continuous rim for smoother cutting.
The type of core that can be used depends on the type of materials that the diamond blade is designed to cut. There are three types of sintered metal-bonded diamond blades according to their manufacturing methods: wholly sintered diamond blades, silver brazed diamond blades and laser welded diamond blades. A wholly sintered diamond blade is made by putting the steel core, together with the diamonds and the metal bond materials, into a mold and sintering it in a sintering furnace equipment; the diameter of wholly sintered diamond blades is not large not more than 400 millimetres. Because it is participating in the sintering process, the steel core cannot be quenched, so the hardness and strength of the core are not high; this means that these types of diamond blade may deform in high-load and high-intensity cutting processes and can exhibit low cutting efficiency. Silver brazed and laser welded diamond blades do not have this weakness because their diamond segments and steel core are treated separately.
The steel core can be quenched and processed with other heat treatments, so its hardness and strength can be high, meaning that the blade can be used in high-load and high-intensity cutting processes with high cutting efficiency and a smaller degree of deformation. Silver brazed; these blades can only be used in wet cuttings. If they are used in dry cuttings, the silver solder may melt and the segments can break from the steel core and become a serious safety hazard. A laser melts and combines the metal of the diamond segment and the steel core creating a stronger weld, which can hold the segments in high temperatures, meaning that laser welded diamond blades can be used to cut many types of stone without water cooling. However, when cutting hard or abrasive materials, e.g. concrete containing reinforcing rebar, laser welded diamond blades should be used with adequate water. Otherwise, it is possible for the diamond segment itself to break or the steel core below the segment to wear and break, creating serious safety hazards.
A diamond blade grinds, rather than cuts, through material. Blades have rectangular teeth which contain diamond crystals embedded throughout the segment for grinding through hard materials; the bond is a term used for the softness or hardness of the powder metal being used to form the segments. The powdered metals hold the diamonds in place; the bond controls the rate at which the diamond segments wear down allowing new diamonds to become exposed at the surface to continue grinding with a "sharp" edge. An important step in choosing a blade is to match the bond to the specific material to be cut. Additional factors to consider are the type and power of the equipment to be used and the availability of water. Harder materials need a softer bonded segment to allow for continuous diamond exposure. Softer materials like asphalt or freshly poured concrete can use a harder segment to resist the increased wear that softer, abrasive materials create. In addition, the diamonds' grit and concentration should match the nature of the material to be sawed.
A lapidary is an artist or artisan who forms stone, minerals, or gemstones into decorative items such as cabochons, engraved gems, faceted designs. A lapidarist uses the lapidary techniques of cutting and polishing. Hardstone carving requires specialized carving techniques. Diamond cutters are not referred to as lapidaries, due to the specialized techniques which are required to work diamonds. In modern contexts a gemcutter is a person who specializes in cutting diamonds, but in older historical contexts it refers to artists producing engraved gems such as jade carvings. By extension, the term lapidary has sometimes been applied to collectors of and dealers in gems, or to anyone, knowledgeable in precious stones; the etymological roots of the word lapidary is the Latin word lapis. In the 14th century, the term evolved from lapidarius, meaning "stonecutter" or "working with stone", into the Old French word lapidaire, meaning "one skilled in working with precious stones". In French, English, the term is used for a treatise on precious stones that details their appearance and properties—particularly in terms of the "stones' powers"—as believed in medieval Europe.
The beliefs about the powers of stones included their ability to prevent harm, heal ailments, or offer health benefits. Lapidary appeared as an English adjective in the 18th century; the earliest known lapidary work occurred during the Stone Age. As people created tools from stone, they realized that some geological materials were harder than others; the next earliest documented examples of what one may consider to be lapidary arts came in the form of drilling stone and rock. The earliest roots of drilling rocks date back to one million years ago; the early Egyptians developed cutting and jewelry fashioning methods for lapis lazuli and amethyst. The lapidary arts were quite well-developed in the Indian subcontinent by early-1st millennium CE; the surviving manuscripts of the 3rd-century Buddhist text Rathanpariksha by Buddha Bhatta, several Hindu texts of mid-1st millennium CE such as Agni Purana and Agastimata, are Sanskrit treatises on lapidary arts. They discuss sources of gems and diamonds, their origins, testing and polishing, making jewelry from them.
Several other Sanskrit texts on gems and lapidary arts have been dated to post-10th century, suggesting a continuous lapidary practice. According to Jason Hawkes and Stephanie Wynne-Jones, archaeological evidence suggests that trade in lapidary products between Africa and India was established in the 1st millennium CE. People of the Deccan region of India and those near the coast of East Africa had innovated their own techniques for lapidary before the 10th century, as evidenced by excavations and Indian and non-Indian texts dated to that period. Lapidary was a significant tradition in early Mesoamerica; the lapidary products were used as status symbols, for offerings, during burials. They were made from shell, jade and greenstones. Aztec lapidaries used string drills made of reed and bone as their lapidary tools. There are three broad categories of lapidary arts: tumbling, cabochon cutting, faceting. Most modern lapidary work is done using motorized equipment. Polishing is done with resin- or metal-bonded emery, silicon carbide, aluminium oxide, or diamond dust in successively decreasing particle sizes until a polish is achieved.
In older systems, the grinding and polishing powders were applied separately to the grinding or buffing wheel. The final polish will use a different medium such as tin oxide or cerium oxide. Cutting of harder stones is done with a diamond-edged saw. For softer materials, a medium other than diamonds can be used, such as silicon carbide, emery, or corundum. Diamond cutting requires the use of diamond tools because of the extreme hardness of diamonds; the cutting and polishing operations are lubricated with water, oil, or other liquids. Beyond these broader categories, there are other specialized forms of lapidary techniques, such as casting, carving and mosaics. Another specialized form of lapidary work is the inlaying of marble and gemstones into a marble matrix; this technique is known in English as pietra dura, for the hardstones that are used, like onyx and carnelian. In Florence and Naples, where the technique was developed in the 16th century, it is called opere di commessi; the Medici Chapel at San Lorenzo in Florence is veneered with inlaid hard stones.
The specialty of micromosaics, which developed in the late-18th century in Naples and Rome, is sometimes covered under the umbrella term of lapidary work. In this technique, minute slivers of glass are assembled to create still life, cityscape views, other images. In China, lapidary work specializing in jade carving has been continuous since at least the Shang dynasty. There are lapidary clubs throughout the world. In Australia there are numerous gem shows, including an annual gem show called the GEMBOREE, a nationwide lapidary competition. There is a collection of gem and mineral shows held in Tucson, Arizona, at the beginning of February each year; the event began with the Tucson Gem and Mineral Society Show and has now grown to include dozens of other independent shows. In 2012, this concurrent group of shows constituted the largest mineral event in the world. Amber Diamond Gemstone Handicraft Jade Pearl Ruby
Mohs scale of mineral hardness
The Mohs scale of mineral hardness is a qualitative ordinal scale characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. Created in 1812 by German geologist and mineralogist Friedrich Mohs, it is one of several definitions of hardness in materials science, some of which are more quantitative; the method of comparing hardness by observing which minerals can scratch others is of great antiquity, having been mentioned by Theophrastus in his treatise On Stones, c. 300 BC, followed by Pliny the Elder in his Naturalis Historia, c. 77 AD. While facilitating the identification of minerals in the field, the Mohs scale does not show how well hard materials perform in an industrial setting. Despite its lack of precision, the Mohs scale is relevant for field geologists, who use the scale to identify minerals using scratch kits; the Mohs scale hardness of minerals can be found in reference sheets. Mohs hardness is useful in milling, it allows assessment of.
The scale is used at electronic manufacturers for testing the resilience of flat panel display components. The Mohs scale of mineral hardness is based on the ability of one natural sample of mineral to scratch another mineral visibly; the samples of matter used by Mohs are all different minerals. Minerals are chemically pure solids found in nature. Rocks are made up of one or more minerals; as the hardest known occurring substance when the scale was designed, diamonds are at the top of the scale. The hardness of a material is measured against the scale by finding the hardest material that the given material can scratch, or the softest material that can scratch the given material. For example, if some material is scratched by apatite but not by fluorite, its hardness on the Mohs scale would fall between 4 and 5. "Scratching" a material for the purposes of the Mohs scale means creating non-elastic dislocations visible to the naked eye. Materials that are lower on the Mohs scale can create microscopic, non-elastic dislocations on materials that have a higher Mohs number.
While these microscopic dislocations are permanent and sometimes detrimental to the harder material's structural integrity, they are not considered "scratches" for the determination of a Mohs scale number. The Mohs scale is a purely ordinal scale. For example, corundum is twice as hard as topaz; the table below shows the comparison with the absolute hardness measured by a sclerometer, with pictorial examples. On the Mohs scale, a streak plate has a hardness of 7.0. Using these ordinary materials of known hardness can be a simple way to approximate the position of a mineral on the scale; the table below incorporates additional substances that may fall between levels: Comparison between hardness and hardness: Mohs hardness of elements is taken from G. V. Samsonov in Handbook of the physicochemical properties of the elements, IFI-Plenum, New York, USA, 1968. Cordua, William S. "The Hardness of Minerals and Rocks". Lapidary Digest, c. 1990
An engraved gem referred to as an intaglio, is a small and semi-precious gemstone, carved, in the Western tradition with images or inscriptions only on one face. The engraving of gemstones was a major luxury art form in the Ancient world, an important one in some periods. Speaking, engraving means carving in intaglio, but relief carvings are covered by the term; this article uses cameo in its strict sense, to denote a carving exploiting layers of differently coloured stone. The activity is called gem carving and the artists gem-cutters. References to antique gems and intaglios in a jewellery context will always mean carved gems. Vessels like the Cup of the Ptolemies and heads or figures carved in the round are known as hardstone carvings. Glyptics or glyptic art covers the field of small carved stones, including cylinder seals and inscriptions in an archaeological context. Though they were keenly collected in antiquity, most carved gems functioned as seals mounted in a ring. A finely carved seal was practical, as it made forgery more difficult – the distinctive personal signature did not exist in antiquity.
Gems were cut by using abrasive powder from harder stones in conjunction with a hand-drill often set in a lathe. Emery has been mined for abrasive powder on Naxos since antiquity; some early types of seal were cut by hand, rather than a drill. There is no evidence. A medieval guide to gem-carving techniques survives from Theophilus Presbyter. Byzantine cutters used a flat-edged wheel on a drill for intaglio work, while Carolingian ones used round-tipped drills. In intaglio gems at least, the recessed cut surface is very well preserved, microscopic examination is revealing of the technique used; the colour of several gemstones can be enhanced by a number of artificial methods, using heat and dyes. Many of these can be shown to have been used since antiquity – since the 7th millennium BC in the case of heating; the technique has an ancient tradition in the Near East, is represented in all or most early cultures from the area, the Indus Valley civilization. The cylinder seal, whose design only appears when rolled over damp clay, from which the flat ring type developed, was the usual form in Mesopotamia and other cultures, spread to the Minoan world, including parts of Greece and Cyprus.
These were made in various types of stone, not all hardstone. The Greek tradition emerged in Ancient Greek art under Minoan influence on mainland Helladic culture, reached an apogee of subtlety and refinement in the Hellenistic period. Pre-Hellenic Ancient Egyptian seals tend to have inscriptions in hieroglyphs rather than images; the Biblical Book of Exodus describes the form of the hoshen, a ceremonial breastplate worn by the High Priest, bearing twelve gems engraved with the names of the Twelve tribes of Israel. Round or oval Greek gems are found from the 8th and 7th centuries BC with animals in energetic geometric poses with a border marked by dots or a rim. Early examples are in softer stones. Gems of the 6th century are more oval, with a scarab back, human or divine figures as well as animals; the forms are sophisticated for the period, despite the small size of the gems. In the 5th century gems became still only 2-3 centimetres tall. Despite this fine detail is shown, including the eyelashes on one male head a portrait.
Four gems signed by Dexamenos of Chios are the finest of two showing herons. Relief carving became common in 5th century BC Greece, most of the spectacular carved gems in the Western tradition were in relief, although the Sassanian and other traditions remained faithful to the intaglio form. A relief image is more impressive than an intaglio one; however inscriptions are still in reverse so they only read on impressions. This aspect partly explains the collecting of impressions in plaster or wax from gems, which may be easier to appreciate than the original; the cameo, rare in intaglio form, seems to have reached Greece around the 3rd century. The conquests of Alexander the Great had opened up new trade routes to the Greek world and increased the range of gemstones available. Roman gems continued Hellenistic styles, can be hard to date, until their quality declines at the end of the 2nd century AD. Philosophers are sometime