Saturday, 29 November 2014

Lapidary Techniques

Saturday, November 29, 2014 Posted by Pink City Pebbles , No comments
The earliest known lapidary work was Stone Age. The early Egyptians developed techniques for cutting and polishing stones as hard as quartz, such as amethyst.

A lapidary is an artist or artisan who forms stone, minerals, or gemstones into decorative items such as cabochons, engraved gems, including cameos, and faceted designs. The primary techniques employed are cutting, grinding, and polishing. Carving is an important, but specialised technique. In modern contexts "gemcutter" typically refers to people who specialize in cutting diamonds, but in older historical contexts it refers to artists producing engraved gems such as jade carvings and the like.

Several common techniques are used in lapidary work:

Sawing a piece of smoky quartz. (Warning! Holding rough by hand during sawing can be hazardous to the stone, the saw, and the cutter! Extreme caution is required.) In most gem sawing, a thin circular blade usually composed of steel, copper, or a phosphor bronze alloy impregnated along the outer edge with diamond grit and rotating at several thousand surface feet per minute literally scratches its way through a gemstone. A liquid such as oil or water is used to wash away cutting debris and keep the stone and the saw blade from overheating, which could cause damage to both the stone and the sawblade.

Several sizes of circular rock saws are frequently used by most gemcutters:
  • A slab saw, typically 16 to 24 inches in diameter, is used to cut stones of several inches thickness into relatively thin slabs (often 1/8 to 3/8 inch thick).
  • A trim saw, typically 6 to 10 inches in diameter, is used to cut smaller stones into thin slabs or to cut small sections out of slabs.
  • A faceter's trim saw, typically 4 inches in diameter, is used with a very thin blade, to saw small pieces of expensive rough.
There are also jigsaws that employ either a reciprocating wire or a continuous thin metal band. These are useful for cutting curved lines that are impossible with circular saws. They are also useful in minimizing waste on extremely valuable rough material.

Grinding, usually with silicon carbide wheels or diamond-impregnated wheels, is used to shape gemstones to a desired rough form, called a preform. As with sawing, a coolant/lubricant (water or oil) is used to remove debris and prevent overheating. Very coarse diamond or silicon carbide, such as 60 grit, or mesh, (400 micron particles) or 100 grit (150 micron particles) is used for rapid removal of stone, and finer abrasive (600 grit - 30 micron, or 1200 grit - 15 micron) is used for final shaping and sanding.

Sanding is similar to grinding but uses finer abrasives. Its purpose is to remove deep scratches left by coarser abrasives during grinding. Since it removes material less rapidly, it also allows more delicate control over final shaping of the stone prior to polishing. For stones with rounded surfaces, a flexible surface such as a belt sander is often used to avoid creating flat areas and promote smooth curves.

Lapping is very similar to grinding and sanding, except that it is performed on one side of a rotating or vibrating flat disk known as a lap, and it is used especially to create flat surfaces on a stone (as in faceting). Laps are often made of cast iron, steel, or a copper-bronze alloy, but other materials can also be used.

After a gemstone is sawed and ground to the desired shape and sanded to remove rough marks left by coarser grits, it is usually polished to a mirror-like finish to aid light reflection from the surface of the stone (or refraction through the stone, in the case of transparent materials). Very fine grades of diamond (50,000 to 100,000 mesh) can be used to polish a wide variety of materials, but other polishing agents work well in many instances. Usually, these polishing agents are metal oxides such as aluminum oxide (alumina), cerium oxide, tin oxide, chromium oxide, ferric oxide (jeweler's rouge), or silicon dioxide (tripoli). Different stones are often very inconsistent in their ease of polishing, particularly in the case of faceted stones, so gemcutters are often very inventive in trying new combinations of polishing agents and polishing surfaces -- often tin, tin-lead, lead, leather, felt, pellon, wood, or lucite laps for flat surfaces such as facets. Rounded surfaces, such as on cabochons, are often polished on felt, leather, cork, cloth, or wood. Polishing removes small quantities of stone and can be used, especially when faceting small stones,to do ultrafine shaping of the stone.

When a gemcutter desires a hole in or through a gemstone (e.g., a bead), a small rotating rod or tube with a diamond tip, or a slurry of silicon carbide and coolant, is used to drillthrough the stone. Ultrasonic, or vibrating, drills are also very effective, but they tend to be costly and thus reserved for high-volume commercial drilling.

Large quantities of roughly shaped stones are often tumbled, i.e., turned at a slow speed in a rotating barrel with abrasives and water for extended periods (days or weeks). By tumbling with progressively finer grades of abrasive (usually silicon carbide) and washing carefully between grades, the stones are gradually smoothed and polished to serendipitous but often very attractive shapes. Tumbling barrels are often hexagonal in outline in order to enhance the stirring action of barrel rotation. An alternative to rotatory tumblers is a vibratory machine, often called a vibratory tumbler, in which the containing barrel vibrates rather than rotates. The more stationary arrangement of vibratory machines makes it much easier to examine the progress of the stones inside, whereas standard tumblers must be halted in order to check progress. In addition to polishing gemstones, tumbling is often used to polish large quantities of metal jewelry.

The Make Over - Stone Cutting & Polishing

Saturday, November 29, 2014 Posted by Pink City Pebbles , , , No comments

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.

A few gemstones are used as gems in the crystal or other form in which they are found. Most however, are cut and polished for usage as jewelry.
The process of cutting and polishing gems is called gemcutting or lapidary, while a person who cuts and polishes gems is called a gemcutter or a lapidary (sometimes lapidarist).

Gemstone material that has not been extensively cut and polished is referred to generally as rough. Rough material that has been lightly hammered to knock off brittle, fractured material is said to have been cobbed.

All gems are cut and polished by progressive abrasion using finer and finer grits of harder substances. Diamond, the hardest naturally occurring substance, has a Mohs hardness of 10 and is used as an abrasive to cut and polish a wide variety of materials, including diamond itself. Silicon carbide, a manmade compound of silicon and carbon with a Mohs hardness of 9.5, is also widely used for cutting softer gemstones. Other compounds, such as cerium oxide, tin oxide, chromium oxide, and aluminum oxide, are frequently used in polishing gemstones.

Several common techniques are used in lapidary work:
  • Sawing
  • Grinding
  • Sanding
  • Lapping
  • Polishing
  • Drilling
  • Tumbling
Using the techniques listed above, gemstones are typically fashioned into one of several familiar forms:
  • Cabochons
  • Faceted stones
  • Beads and Spheres
  • Inlays
  • Intarsias and Mosaics
  • Cameos and Intaglios
  • Sculptures
There are various commercial cutting operations across India. These small factories cuts thousands of carats of sapphire annually. Pink City Pebbles have been doing this since years and have skilled persons in this field. The two main classifications are stones cut as smooth, dome shaped stones called cabochons, and stones which are cut with a faceting machine by polishing small flat windows called facets at regular intervals at exact angles.

Stones which are opaque such as opal, turquoise, variscite, etc. are commonly cut as cabochons. These gems are designed to show the stone's color or surface properties as in opal and star sapphires. Grinding wheels and polishing agents are used to grind, shape and polish the smooth dome shape of the stones.

Tuesday, 25 November 2014

About Us

Tuesday, November 25, 2014 Posted by Pink City Pebbles No comments
About Us

Pink City Pebbles deals with Semi-precious Gemstones cutting and polishing. It is the source of every attractive ornaments we adore. From 'Raw' Stones to a well Designed or Fine Cut/polished Stone, Pink City Pebbles does it all. Our products are not only available across India but also outside India to various other countries.  

Pink City Pebbles have a long tradition of providing quality service to its customers. We continue to expand our horizons to meet emerging customer need. Pink City Pebble's skilled and innovative workforce are the best in the market. Our fine work and expertise is highly recognized and appreciated.

Our Story

Coming Soon... !!


Gem Value

Tuesday, November 25, 2014 Posted by Pink City Pebbles , No comments

There is no universally accepted grading system for gemstones. Diamonds are graded using a system developed by the Gemological Institute of America (GIA) in the early 1950s. Historically, all gemstones were graded using the naked eye. The GIA system included a major innovation: the introduction of 10x magnification as the standard for grading clarity. Other gemstones are still graded using the naked eye.

A mnemonic device, the "four Cs" (color, cut, clarity and carats), has been introduced to help the consumer understand the factors used to grade a diamond. With modification, these categories can be useful in understanding the grading of all gemstones. The four criteria carry different weight depending upon whether they are applied to colored gemstones or to colorless diamonds. In diamonds, cut is the primary determinant of value, followed by clarity and color. Diamonds are meant to sparkle, to break down light into its constituent rainbow colors (dispersion), chop it up into bright little pieces (scintillation), and deliver it to the eye (brilliance). In its rough crystalline form, a diamond will do none of these things; it requires proper fashioning and this is called "cut". In gemstones that have color, including colored diamonds, it is the purity and beauty of that color that is the primary determinant of quality.

Physical characteristics that make a colored stone valuable are color, clarity to a lesser extent (emeralds will always have a number of inclusions), cut, unusual optical phenomena within the stone such as color zoning (the uneven distribution of coloring within a gem) and asteria (star effects). The Greeks, for example, greatly valued asteria in gemstones, which were regarded as powerful love charms, and Helen of Troy was known to have worn star-corundum.

Aside from the diamond, the ruby, sapphire, emerald, pearl (not, strictly speaking, a gemstone) and opal have also been considered to be precious. Up to the discoveries of bulk amethyst in Brazil in the 19th century, amethyst was considered a precious stone as well, going back to ancient Greece. Even in the last century certain stones such as aquamarine, peridot and cat's eye (cymophane) have been popular and hence been regarded as precious.

Nowadays such a distinction is no longer made by the gemstone trade. Many gemstones are used in even the most expensive jewelry, depending on the brand name of the designer, fashion trends, market supply, treatments, etc. Nevertheless, diamonds, rubies, sapphires, and emeralds still have a reputation that exceeds those of other gemstones.

Rare or unusual gemstones, generally meant to include those gemstones which occur so infrequently in gem quality that they are scarcely known except to connoisseurs, include andalusite, axinite, cassiterite, clinohumite and red beryl.

Gem prices can fluctuate heavily (such as those of tanzanite over the years) or can be quite stable (such as those of diamonds). In general per carat prices of larger stones are higher than those of smaller stones, but popularity of certain sizes of stone can affect prices.

Monday, 24 November 2014

Stone Classification

Monday, November 24, 2014 Posted by Pink City Pebbles , No comments

The traditional classification in the West, which goes back to the Ancient Greeks, begins with a distinction between precious and semi-precious; similar distinctions are made in other cultures. In modern usage the precious stones are diamond, ruby, sapphire and emerald, with all other gemstones being semi-precious. This distinction reflects the rarity of the respective stones in ancient times, as well as their quality: all are translucent with fine color in their purest forms, except for the colorless diamond. Other stones are classified by their color, translucency and hardness. The traditional distinction does not necessarily reflect modern values, for example, while garnets are relatively inexpensive, a green garnet called Tsavorite, can be far more valuable than a mid-quality emerald. Another unscientific term for semi-precious gemstones used in art history and archaeology is hardstone. Use of the terms 'precious' and 'semi-precious' in a commercial context is, arguably, misleading in that it deceptively implies certain stones are intrinsically more valuable than others, which is not the case.

In modern times gemstones are identified by gemologists, who describe gems and their characteristics using technical terminology specific to the field of gemology. The first characteristic a gemologist uses to identify a gemstone is its chemical composition. For example, diamonds are made of carbon and rubies of aluminium oxide. Next, many gems are crystals which are classified by their crystal system such as cubic or trigonal or monoclinic. Another term used is habit, the form the gem is usually found in. For example diamonds, which have a cubic crystal system, are often found as octahedrons.

Gemstones are classified into different groups, species, and varieties. For example, ruby is the red variety of the species corundum, while any other color of corundum is considered sapphire. Other examples are the Emerald (green), aquamarine (blue), red beryl (red), goshenite (colorless), heliodor (yellow), and morganite (pink), which are all varieties of the mineral species beryl.

Gems are characterized in terms of refractive index, dispersion, specific gravity, hardness, cleavage, fracture, and luster. They may exhibit pleochroism or double refraction. They may have luminescence and a distinctive absorption spectrum.

Material or flaws within a stone may be present as inclusions.

Gemstones may also be classified in terms of their "water". This is a recognized grading of the gem's luster and/or transparency and/or "brilliance". Very transparent gems are considered "first water", while "second" or "third water" gems are those of a lesser transparency.

Sunday, 23 November 2014

Semi Precious Stones - Significance

Sunday, November 23, 2014 Posted by Pink City Pebbles , , , No comments

In today's ornament industry we use heaps of beautiful natural semi precious stones. Many of the stones are said to have exquisite properties which brings positive energy to our life. Here are a few which we are using at the moment -
  • Chrysoprase - Boosts creativity and brings out our talents.
  • Turquoise - Promotes good fortune.
  • Agate - Protects and heals.
  • Pearl - Seen as a symbol of innocence and purity.
  • Rose Quartz - Encourages romance and self love.
  • Jade - Attracts love and prosperity.
  • Amazonite - Brings luck.