Gem cutting is a marvelous amalgam of science and art. Every polished gem starts as a piece of rough. It’s the skill and art of a gem cutter who unlocks the stone’s hidden beauty and optical effects in a way that is almost magical.
Today, the market for colored gemstones has become more sophisticated. Discerning collectors look at the rarity factor, but also want a stone that is beautiful in every aspect, including the cutting and polish.
In this blog, we explore the highly skilled process that turns a rough gemstone crystal into a work of art. So get ready to be enthralled, as we demystify the magical journey of a rough crystal’s transformation into a sparkling, beautifully finished cut gem.
- What Is Gem Cutting?
- What Is A Lapidary?
- The History Of Gem Cutting
- Factors To Be Considered When Cutting Gemstones
- How To Cut Gemstones
- Grinding/Pre Forming
What Is Gem Cutting?
The art of cutting and polishing gemstones is referred to as ‘Gem Cutting’.
If the gem is uncut, its value would be significantly less. Even if a rough crystal seems dull and uninspiring at first, every step of the cutting process moves it closer to its full potential, thus taking the viewer’s breath away.
Depending upon the hardness of stone, different cutting techniques are adopted for different precious and semi-precious stones.
The basic manufacturing techniques—sawing, bruiting, blocking, and polishing—are performed with the goal of obtaining the greatest value from a specific piece of rough.
What Is A Lapidary?
A lapidary is an artist who cuts, shapes and facets gemstones in different styles (faceted, cabochon, cameos etc.) in order to reveal their intrinsic beauty.
The lapidarist studies a stone’s features and quality to determine the best cut and accomplishes the process by hand, with a machine, or both.
When the cutter picks up a piece of rough in order to plan the cut, he must make many complex decisions such as how the stone will be cut, with respect to the rough stone’s original shape, color, and weight.
The creativity that comes from the well-practiced hands of lapidaries is what keeps the gem and jewelry industry fresh.
The work of a lapidarist can broadly be classified into:
- Gemstone Pre- Shaper
- Gemstone Facet Maker
- Gemstone Polisher
The History Of Gem Cutting
Man has been cutting and fashioning gemstones for hundreds of years in an age old quest to enhance their inherent beauty.
Originally, gemstones used to be decorated by scratching figures, symbols or letters onto them. This, in turn, led to the art of engraving.
From drawings chiseled in cave walls to blades made from sharp flakes of stone, ancient cultures developed the basic techniques that gave rise to modern drilling, tumbling, polishing, and more.
Over the millennia, gemstone cutting has evolved into an intricate art form utilizing advanced technologies.
The origins of gemstone cutting can be found in India. Up until 1400 AD, there was very limited polishing done. This was mainly to improve the lustre and remove unsightly blemishes.
The town of Idar-Oberstein in Germany soon emerged as the gem cutting capital of the world and became the center of agate and colored stone cutting in the 16th Century.
The major cutting centers today are India, Thailand, Sri Lanka, and Brazil.
Factors To Be Considered When Cutting Gemstones
A lapidary must consider a number of variables before cutting a gemstone. These include:
- The shape of the rough and how it can be utilized to maximize yield.
- The position of fractures/ inclusions which could affect the clarity of the stone.
- Ensuring that the most attractive color is visible when the stone is viewed face-up.
- The correct angles and proportions which will be needed to maximize brilliance.
- Relation between value and size. Gems of lesser value are often cut to standard/uniform sizes. But with precious gemstones, there’s freedom to cut the stone to reflect its natural beauty.
- Balance between economics and aesthetics.
- How to juggle these factors to maximize profits.
How To Cut Gemstones
There are various stages in gemstone cutting and polishing. A good cutter will perform each step with intuition and skill leading to a symmetrical, scintillating, and beautiful finished piece.
To achieve a variety of gemstone styles, from a classic brilliant cut to a trendy briolette cut, lapidaries rely on the following processes and techniques:
The whole process begins with the rough crystal.
The quality of rough has a strong impact on a gem’s final appearance.
To get the most out of a gemstone, a skilled lapidary will first examine the rough to get a sense of shape, symmetry and balance.
This takes considerable experience and a good eye, since evaluating a rough stone is more challenging than evaluating a finished gem.
Factors To Be Considered:
- First consideration is whether the rough is transparent, translucent or opaque. Usually, cutters only facet transparent rough, while opaque stones are suitable for cabochons. If the material is facet-grade, the cutter has to decide which part of the stone to facet and what shape to cut.
- Some gems have cracks, fissures, cleavage and fractures. A cutter must carefully examine each piece from all angles, to detect the position and extent of these flaws.
He must also examine the nature and location of inclusions, such as crystals, feathers, bubbles, etc.
- Besides inclusions, color zoning & distribution is also considered. In the most desirable rough, color is evenly distributed throughout the stone.
After these considerations, the cutter decides how he will orient the cut – where the table will sit and where the pavilion will be.
Tools for Assortment:
- 10x Loupe
- Marking Pencil
- Sorting Pad
- Oil (to see the transparency)
- Weighing machine
Before grinding or faceting can begin, workers saw the rough. At this stage, the cutter decides whether a piece of rough will become a single large stone or a number of smaller ones. Sawing divides large rough into usable sections. It also removes waste areas.
In most gem sawing, a thin circular blade is used, which is usually composed of steel, copper, or an alloy and impregnated with diamond grit along the outer edge. It rotates at several thousand surface feet per minute and scratches its way through a gemstone.
A liquid such as water is used to wash away cutting debris and keep the stone and the saw blade from overheating.
Several sizes of circular saws are frequently used by gem cutters:
- Slab saw– It is typically 16-24 inches in diameter, and is used to cut stones of several inches’ thickness into relatively thin slabs.
- Trim saw– It is typically 6-10 inches in diameter, and is used to cut smaller stones into thin slabs or to cut small sections out of slabs.
- Faceter’s trim saw– Typically 4 inches in diameter, and is used with a very thin blade, to saw small pieces of expensive rough.
Tools for Sawing:
- Sawing Machine
- Sawing Blade/ Diamond blade
- Water tank
- Marking Pencil
- Gloves/Finger cap
- Protective mask
- Eye protector
Choosing the shape and orientation of the stone is an art. The preforming stage has the greatest impact on the value of the finished gem, so it requires the attention of workers.
At this stage, the cutter shapes the rough to a desired form by grinding it, and makes the stone’s basic shape & proportions including the table facet, crown and pavilion.
This rough shape is called a preform. Preforming is usually done by hand with fairly coarse diamond abrasive that cuts quickly.
Factors To Be Considered:
- Factors such as achieving maximum clarity, transparency and check on weight loss are considered during this process.
- Decision is taken as to which side should be the Table.
- Small inclusions can be concealed by shaping the stone so they fall near the girdle. They should not be positioned under the table facet, where they are most visible.
- Decision regarding locating the source of color in the stone is taken.
The side of stone having more color is generally kept as a pavilion in order to distribute color throughout.
Tools for Pre Forming:
- Grinding wheel
- Coolant supply system
- Diamond lap for rough grinding (Grit no. 260,360)
- Diamond lap for fine grinding and sanding (Grit no. 1200)
- Dop stick
- Marking pencil
- Eye protector
Calibration enables us to produce stones that are uniform in size and shape.
It is an important process in the mass produced jewelry business.
In automatic casting machines used for jewelry making, cavities for studding gems are made in uniform dimensions and use of a calibration machine enables to make the stones in standard sizes and in less time.
Factors To Be Considered:
- Uniformity of shape.
- Diameter of the stone with specified tolerance.
- Height of the piece.
- Girdle thickness depends upon the size and shape of the stone.
Tools For Calibrating:
- Calibrating machine & its tools
- Diamond Lap (Grit no. 360)
- Coolant supply system
- Master shape piece
- Measuring gauge
- Iron dop stick
- Dop stand
- Hot plate
- Hard glue (araldite)
- Attach the pre-shaped stone to the iron dopstick using hard glue such as araldite.
- Fix the dopstick to the dop stand.
- Start the heater/hot plate and heat for minimum 15 minutes.
- After switching off the heater, let the dopstick cool down.
- Insert the dopstick into the colet of the machine.
- A master piece is added to the machine except for round shape, to get the perfect size and shape.
- Operate the calibrating machine and adjust it according to the desired size.
Dopping is the process of fixing the gemstone onto a dopstick.
After preforming, the cutter secures the preformed stone with adhesive onto a wooden or metal dopstick. The dopstick holds the preform and gives the cutter greater control during faceting.
Tools for Dopping:
- Dop stick
- Spirt lamp/gas
- Transferring Jack/ V block
- Select a dop stick according to the stone’s size and cutting style. Example: 8 facet dopstick, 12 facet dopstick, etc.
- Make the stick with wax according to the stone’s size.
- Heat the top of wax under heat lamp and dop the stone from pavilion side, in order to make the crown side.
- Align and center the stone on the dopstick at 90-degree angle, with a V-block.
- After the stone is cut and polished, heat the wax and pull the stone.
- Clean the stone with a denatured alcohol or other solvents such as thinner.
- To make the pavilion side, dop the stone from crown side and align the crown & pavilion facets above each other.
- Once the stone is completed, remove it from the stick and clean it.
The process of cutting fine rough into a scintillating finished gemstone is called faceting.
This is a skilled process where a cutter carefully places a number of flat geometric facets onto the table and pavilion of a gemstone.
Facets are cut on the surface of a gem at definite angles to bring out the hidden beauty and brilliance.
The timing and skills involved here are incredible. The main objective of faceting a gemstone is to maximise its beauty by internal refraction and reflection.
Tools for Faceting:
- Faceting machine
- Diamond lap for cutting (Grit no.1200)
- Dop stick
- Coolant system (water)
- 10x loupe
The gem is held at a precise angle against a horizontal cutting wheel/disc called a lap to cut the facets.
Diamond impregnated cutting laps are suitable for faceting gemstones. The friction inherent in grinding and faceting a gem creates a lot of heat. To keep things cool, the lap is lubricated by running water, which acts as a coolant.
Using a handheld faceting tool, the cutter determines the height, angle, and index triangle to place individual facet separately on the crown and pavilion.
Height will control the depth to which each facet is cut, angle controls the plane on which the facets are cut and the index controls the placement of facets around the shape.
When cut at the right angles and depth, the facets create a dazzling interplay of light as it passes through the gemstone.
Faceting is done using table-top machines that give lapidaries control over every angle.
In the industry, various types of faceting machines are used.
All faceting machines have an arm that holds the gemstone to be cut on a dopstick. This arm must be precisely positioned at a fixed angle and must be rotatable to put each facet in the right place.
This can be done as simply as using holes drilled into a board, which is called a ‘Jam-Peg machine’, or using an index gear in the ‘Facetron machine’.
Once all the facets are cut, the process of polishing begins. The goal is to achieve a mirror-like finish, and remove tiny scratches and marks left from the grinding process.
A well cut and polished gem will reflect light beautifully for an even, overall glimmer and glitter effect.
Tools for Polishing:
- Polishing machine
- Metal polishing laps
- Copper plate for hard stones
- Alloy plate for stones with hardness less than 7
- Diamond powder
- 14000 grit-1 micron
- 8000 grit- 3 micron
- 3000 grit- 7 micron
- Emery paper
- 10x Loupe
After a gemstone is sawed, grinded, sanded and faceted, it is polished. Each facet is polished individually to a high sheen, giving the stone a fine lustre and sparkle. A polished facet will exhibit a uniform smoothness, free from marks and scratches.
The cutter uses a special polishing lap which is primed with very fine diamond powder.
Other polishing agents work well in many instances. Usually, these polishing agents are metal oxides such as aluminium oxide, cerium oxide, tin oxide, chromium oxide, ferric oxide.
The last step is to polish the girdle of the stone. A polished girdle adds extra brilliance and also makes the gem more attractive.
And it’s done! After washing away the grit and residue, the beautiful new gem is ready for its big reveal.
Next time you look at a beautiful faceted gemstone, appreciate the great skill and pure miracle that it has survived several hundred million years under pressure and heat, deep under the Earth and then successfully navigated the path through the cutting process.