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Gemstone cutting : Facet machine components

Written by Erick Razo On April 2, 2018.

Now that we have learned how to pick out a rough diamond and what makes a standard round brilliant shape, the fun begins! In this blog we will begin to explain the process on how to polish and give shape to a rough stone. However, none of this can happen without the proper tools. Before we begin doing that, it is highly recommended to take facetting classes. Equipment can be expensive and it is a good idea to find some of this classes to help you try different materials and techniques used to facet a gemstone. This blog post is to help us understand the equipment used to perform the gem faceting.

 

Facet Machine-A device that allows the user to place and polish facets onto a mineral specimen. There are two major components of a faceting machine: The mast/head assembly, and the grinding wheel, or lap. A rough piece of mineral is attached to the head, and through angle, rotation, and height adjustments of the head, the mineral is lowered into contact with the grinding wheel until a facet has been ground. The mast assembly is the heart of the faceting machine. The rest of the machine is simple in construction, including the arbor for the grinding wheel, the motor that runs the arbor, a drip tank, and the controlling switches. These are described below:

machine

Arbor: Similar to the prong in the middle of a record player that you put a vinyl on, the lap (or grinding wheel) is placed onto it, and the arbor is machined to run perfectly flat when turning.

 arbor

Arbor Nut: The screw that fits through the top of the lap and secures it to the arbor.

 arbor nut

Motor: Typically the motor is housed beneath the machine and is attached by one of several means to the arbor. Motors are always velocity-variable and some can be reversed, i.e. they can turn clockwise as well as counterclockwise.

 engine

Drip Tank: The drip tank serves two purposes. 1) The friction produced from contact between the rough and the lap creates heat, which can damage the lap and create stress fractures in the stone. The drip tank allows the user to choose a drip rate via spigot and position the spigot over the lap, nearer or farther from the arbor. 2) The dust produced from grinding minerals can cause pulmonary disease if inhaled. The flow of water from the trip tank captures the particles in a slurry, which drains into a rubber container around and below the lap. This container has an exit tube that drains into a second receptacle.

DripTank

Controls: The controls are generally simple and control the rotational velocity of the lap—the key control—and sometimes the direction of spin.

controls

As stated above, the mast assembly is what makes a faceting machine a faceting machine. Its components are as follows:

Mast: A vertical pole mounted into the base of the machine on which the assembly is positioned. The pole must be machined with extreme care to ensure its perpendicularity to the lap. This is so that, when the angles for facets are chosen, they are placed at the correct angle. Facets at incorrect angles can mean a gemstone that is lifeless or transparent rather than sparkly.

mast

Dop: The piece of rough gemstone is glued or attached with hot wax to the end of a brass or steel rod, known as a “dop” or “dop stick.” The other end of the dop is placed into the quill of the faceting head. The exposed piece of rough usually becomes the bottom of the stone, known as the pavilion. Once the pavilion is faceted and polished, a jig is used to attach the pavilion to another dop, and the rough side of the stone is freed from its dop. This rough side will now become the top of the stone, or the crown.

 dop

Quill: The dop is inserted into the quill, which is lowered toward the lap to place a facet. The quill is the part of the machine that is held in the hand during faceting. The other end of the quill is attached to the main head of the assembly.

 quill

Index Wheel: If you view a gemstone from the top, you will see it has some type of symmetry. Most most round brilliant stones will have eightfold symmetry; emerald cuts have two or fourfold. In order to cut facets around a stone, the quill must be rotated around its long axis. The index wheel is what allows this to be done in a repeatable, accurate manner. For example, the index wheel may have 64 teeth. If a round stone with eightfold symmetry is being cut, the index will be set at 0, 8, 16, 24, 32, 40, 48 and 56 for each of the main facets around the stone. If a square stone is being cut, only 0, 16, 32 and 48 would be used.

 IndexWheel

Angle Adjustment: Faceting machines differ greatly in the mechanism for setting the angle of the facet. Essentially, the angle is set and the quill will then lower to exactly that angle before physically being stopped or otherwise indicating arrival at the desired angle.

 AngleSet

Height Adjustment: The depth of a facet is determined by how high or low the head assembly is, relative to the lap. The way this is determined is by choosing an angle, lowering the quill (with dop inserted) to that angle, and then observing whether and how deeply the piece of rough is contacting the lap. Generally the first adjustment will set the rough just touching the lap, so that a very shallow facet will be placed. The head can then be lowered by a micro-adjustment and the facet can be cut and re-cut until it is of a desired depth. Many machines allow the head to be untightened from the mast and slid up and down for gross adjustments, and then have a separate mechanism for making fine adjustments up and down.

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 finalized set up

 

In the next installment of this blog series, we will begin to explain and look at the cutting process.

 

Gemstone Cutting : Terminology

Written by Erick Razo On February 28, 2018.

Which shape is the best? The age old debate in the jewelry industry continues every year as shapes go in and out of style. However, there is one shape that continues to be the most highly sought after and timeless shape of all…the round brilliant cut!

Now, you may be asking “What is involved in a standard brilliant cut?” In this blog we will talk about the history and terminology of the standard round brilliant and how each part is cut to precise measurements that allows the gemstone to perform at its maximum capabilities.

The first faceted stones appeared in the late 14th century. Many lapidaries passed down the knowledge of gem faceting as family secrets. During the 19th century, the art of faceting gemstones became available to amateurs and hobbyists. Fast forward to today and you can find all kinds of literature and videos on how to perform this art. The standard round brilliant begins with the craftsman rounding out the rough stone, then a combination of facets in geometrical patterns are cut around the stone. This maximizes the optical properties of the gem and will generate brilliance that is pleasing to any beholder. There is a total of 57 facets in a standard brilliant, however, this can vary depending on the stone.

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The Crown

The crown is the top section of the gemstone. It is approximately ⅓ of the height of the finished gem. A total of 33 facets make up the crown. The facets are divided into 8 main facets, 16 girdle facets, 8 star facets and 1 table facet.

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The Pavilion

This is the bottom section of the gemstone. It is approximately ⅔ of the height of the finished gem. A total of 24 facets make up the pavilion. The facets are divided into 8 main facets, 16 girdle facets.

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The Girdle

This is the section of the gemstone that connects the crown and the pavilion. The maximum height of a girdle in a standard brilliant, must not exceed 5% of the finished gem’s height.

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The Culet

This is the very bottom point of a gemstone. It can be cut as a small, flat facet to prevent the gem from fracturing. This is a common practice to help the durability of stone.

Culet

There you have it; this is the parts of a standard round brilliant. Not all gemstones are cut into this shape, many times the shape is dependant on what type of stone is being cut, and how included the rough is. The decision of what shape to cut the stone into is essential as it will affect all the steps that we will learn about in the next blog post.

 

Gemstone Cutting : Picking Rough

Written by Erick Razo On February 10, 2018.

Gemstones have been part of history since ancient times; their beauty has captivated kings, pharaohs, emperors and everything in between. Fast forward to today and the beauty of gemstones, continue to fascinate us but how does a gem become so beautiful? There are many steps necessary to facet a stone from its rough form to its beautiful finalized form. This series of blog posts are focusing on each step of the faceting process. Today we begin with the first step in the process.

Step One: Selecting the rough.

Rough is the term used to describe the gemstone that has not yet been polished or cut. All gems have unique crystal structures that determine the way they grow and can affect the shape that they will be polished into. When choosing rough, these three factors are essential: clarity, color, and cleavage.

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Sapphire rough, pictures courtesy of GIA.

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Aquamarine rough, pictures courtesy of GIA.

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Topaz rough, pictures courtesy of GIA.

The clarity or the clearness of the stone is determined by the amount of inclusions, cracks or other minerals within the stone. To be able to decide on the clarity, gem cutters utilize oils or liquids that can help them see inside the crystal from the outside, just like a window. Under at least ten power magnification, gem cutters then look for any factors that might affect the clarity or become a potential threat to the structure of the finalized piece.

looking though

The goal is to find a stone that does not contain a lot of inclusions. Which is easier said than done. The art of faceting a stone allows for the cutter to find and analyze the best way to deal with any inclusions in the stone. Once the clarity is analyzed, the orientation of cutting gets mapped out for the maximum recovery of stone weight. A wrong decision in the cutting orientation can be costly and could even cause a complete discard of the rough.

The next step is color, which is the most critical value factor of this entire process of choosing a rough crystal.The term color zoning refers to the uneven distribution of color within a gemstone. Which leads to a question is the color uniform through the entire rough? Is it lighter one side more than the other? Many stones contain more than one band of color, is essential to orient the banded rough so that the pavilion (bottom part of a faceted gemstone) is entirely within the banding when is cut. The pavilion must not protrude past the color zone point, to avoid a loss of the desired color.

color zoning

Obvious color zone in Emerald Even color in Emerald

Cleavage – The tendency of a mineral to break along flat planar surfaces as determined by the structure of its crystal lattice. These two-dimensional surfaces are known as cleavage planes and are caused by the alignment of weaker bonds between atoms in the crystal lattice. The cleavage planes will help orient the stone to the angles needed to prevent the stone from chipping.

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Now we know the basics of picking rough, is a skill that takes time to develop. Remember that practice makes perfect! In our next post, we will begin to identify the parts needed to polish the rough into a beautifully polished gem.

 

The Wonderful World of Color PT.13: Amethyst

Written by Erick Razo On February 8, 2018.

Can you believe that February is here already?! This month we celebrate the most powerful of all feelings, love. We express this love through gifts such as roses, chocolates, teddy bears, a candle light dinner and sometimes a nice bottle of wine. In the gemological world, there is a stone that is highly associated with love and ironically is also associated with wine. This month we will talk about Amethyst.

Cushion

Origins

When you think of a purple gemstone, most likely you said “Oh! Amethyst.” In that case you would be correct, it is the most commonly associated with the color purple. The ancient Greeks believed Amethyst was closely related to Bacchus, the god of wine due to its colors. Which is why it obtained its name from the greek word Amethystos, which means “not drunk” or a “remedy against drunkenness.” They believed the gemstone had the power to prevent drunkenness, because of that many Amethyst chalices were created. It was also believed that if you wore an Amethyst, you would have a sharp mind and quick intelligence, especially when it came to business and on the battlefield. Amethyst had the same value as Ruby, Emerald and Sapphire until the late 1800’s when vasts deposits were found in Brazil. This discovery allowed for the Catholic church to create many rings for their bishops. These rings would be carved with an insignia of sorts to represent each bishop. This was really important to them as Amethyst was the emblem of one of the twelve apostles. Many bishop rings continue to be set with Amethyst. St. Valentine, patron of love, wore an Amethyst ring with cupids image carved into it, hence the association of love with Amethyst.

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Geography of Amethyst

Brazil is the main producer of Amethyst in the world, due to its proximity to Brazil. They can also be found in Uruguay. Amethyst from Zambia is considered to have some of the most beautiful colors for this stone. Arizona in the United States also has an abundance of gem quality Amethyst.

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Chemical Composition, Crystal Structure and Physical Properties

Amethyst is the purple color of the quartz mineral species. They grow in large six sided crystals with pyramid like points at the end. They can grow quite large and fetch high prices by collectors. Amethyst is formed by a mixture of silicon and oxygen called silicon dioxide and it presents itself as a mineral in the form of quartz.

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Amethyst Jewelry

Amethyst color pallet has a range of cool bluish to reddish purples. They can exhibit some deep, dark purples as well as a light lavender color.  Because of its abundance, they can be quite affordable and can be used in rings, bracelets, earrings, pendants and can even be carved into all kinds of shapes. They come in many sizes and shapes, making them great candidates for a lot of jewelry design.

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Wear and care of Amethyst

Amethyst has a 7 on the Moh’s scale. The Moh’s scale of mineral hardness characterizes the scratch resistance of various minerals on an exponential scale from 10 to 0. The top of the scale is Diamond at 10 and graphite at 0. Due to its fair hardness, Amethyst is ideal for jewelry wear, but it should not be subjected to heavy everyday wear. With the right care and the right mounting, you can create a piece that will last for decades.

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Elegant, simple, and charming are some of the words that can be used to describe the beautiful Amethyst. This month is all about celebrating love, the emotion that overpowers all others. An emotion which makes us smile, makes us feel alive, and helps us find an inner strength that we did not know we had. Express your love to your loved ones whether through words, a nice candle light dinner, a teddy bear, roses, or better yet a beautiful Amethyst jewelry piece. Come in and let us to show you the wonderful world of color.

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The Wonderful World of Color PT.12: Garnet

Written by Erick Razo On January 9, 2018.

Some of us have the joy of having siblings, and while they can be quite annoying and infuriating, they are also some of our favorite people in the world. For many parents it is fun to see how alike their kids can be, but the most fascinating part is to see how different they are from each other. The gemological world has their own set of siblings that are pretty close to each other, but like all siblings, they differ in more ways than one. We will begin the year looking at Garnet.

rough 2 rough

Origins

Garnets have been around for centuries, some of the oldest garnets date back to ancient Egyptian civilizations. They symbolize power and passion and because of that they were used to adorn the jewelry of pharaohs. All of that changed when Cleopatra ascended to the throne as Pharaoh of Egypt. Because of her love for Emeralds, She changed the styles and colors of the jewelry worn at the time (learn more about this in our Emerald blog post (the-wonderful-world-of-color-pt-4/). Garnet obtained its name from the Latin name Malum Granatum, which means “red pomegranate seeds.” Many Roman officials would use their signet rings to stamp official documents, and most of those rings contained carved Garnet crystals, even today you can find Garnet crystals in many signet rings. Then in the Middle Ages, Garnet reached its climax of popularity due to their beautiful red color and abundance. At that time they were worn by clergy and nobility as symbols of power and love.

signet rings

Geography of Garnet

Garnets can be found in Brazil, Russia, Thailand, Kenya and other parts of the Middle East. Tsavorite Garnet (known for its beautiful green color) is mined Campbell Bridges. It obtained the name “Tsavorite” because of the proximity to Tsavo National Park in Kenya.

 

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Chemical Composition, Crystal Structure, and Physical Properties

Garnets are a set of closely related minerals that form a group. The group is divided into a species, which are classified by what chemical elements compose the Garnet, for example Iron, Chromium, Calcium, Silicon, Aluminum, etc. Finally, each garnet gets a variety depending on what species they come from and how they are chemically composed. All Garnets grow in metamorphic rocks, this type of stone is found on every continent and can contain many minerals that can determine how the Garnet forms. They essentially share the same crystal structure, but vary in chemical composition. Many Garnets are actually a mixture of two or more other Garnets.

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There are over twenty different garnet species, here is a list of the ones that are commercially important as gems:

Tsavorite Garnet- This Garnet is known for its intense green color. The primary deposit for this gem is near Kenya.

tsavorite

Demantoid Garnet- This Garnet is known for its greenish yellow colors.  Considered to be the Garnet with the most brilliance.

demantoid

Rhodolite Garnet - Known for its purplish red color, it is a combination of Almandine and Pyrope Garnets.

Rhodolite Garnet , 8.27 ct , cut by David Clay, Fallbrook, CA.

Spessartine Garnet - This Garnet is known for its orange to yellow colors. It was not seen in jewelry until the late 1990′s when deposits of it were discovered in Namibia and Mozambique.

spessartine

Almandine Garnet - Known for its red color, is one of the most common varieties of garnets. This type of Garnet is also used in the industrial sector as an abrasive.

almandine

Pyrope Garnet - This is the most common variety of Garnet and is known for its intense, beautiful red color. Because of its rich red color, many thought that they were Rubies for a long time.

pyrope

Uvarovite Garnet - This Garnet has a green color that strikes as Emerald, but the crystals tend to be too small for jewelry use. They are often sought after by collectors.

uavorite

Garnet Jewelry

As we have learned, Garnets actually have a large color palette that includes red, green, orange, pinkish, pinkish orange, purplish red and rarely some blue. This allows jewelers and designers to create astonishing and breathtaking pieces of jewelry. Earrings, rings, bracelets, and pendants can be fashioned with the exquisite color palette of Garnet.
earrings pendant

Wear and Care of Garnet

Garnet ranks 6.5-7.5 on the Moh’s scale. The Moh’s scale of mineral hardness characterizes the scratch resistance of various minerals on an exponential scale from 10 to 0. At the top of the scale is Diamond ranking at 10 and Graphite at 0. Due to its excellent hardness, Garnet is ideal for everyday wear. In the right mounting with the proper protection, Garnet will last a long time.

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Garnets are a big family, each one having their different colors and properties that differentiate them from each other. Just like a family, each member has a different personality and way of expressing themselves, but we all share one thing–the love we have for each other. This January, come by and look at all the different colors that Garnet has to offer.

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