What are Simulated Diamonds?

What are Simulated Diamonds? Properties, Applications, and More
Some diamonds are real, some are synthetic, while some are simulated. And we are here to know about simulated diamonds. Let's take a look...
TAGGED UNDER: Synthetic Diamonds
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Simulated diamonds are not diamonds at all; but imitations that appear like a diamond. Cubic Zirconia (CZ), moissanite, etc., are diamond simulants as they look like diamonds, but have different chemical properties. Therefore, many experts argue that it is inappropriate to call simulated diamonds, 'diamonds'; they should be simply known as simulants.

Simulated Diamonds - A Flashback
The history of making simulated diamonds dates back to the eighteenth century. In the earlier times, glass, rhinestone, etc. was used for making antique jewelry. Later, in the 20th century, other simulants like spinel, white sapphire, strontium titanate, etc. were created. It was not until 1976 that Cubic zirconia, or popularly known as CZ, was created. Although it was also synthesized in the earlier times, it gained a lot of popularity later due to its extreme similarity with the white diamond. However, with the creation of moissanite, there is now a tough competition for cubic zirconia (CZ), which was absent all the while.

The Technology Behind Simulated Diamonds
There are two major methods used to create simulated diamond crystals. The first and most popular method, which was devised by GE, is known as the High Pressure High Temperature (HPHT) method. There too, there are two different press designs which are used to grow diamond crystals. The first is the method used by Howard Tracy Hall, which is called the belt press method. In the belt press method, two anvils, one from up and one from down, supply the pressure and heat currents to a cylindrical volume. The second method is known as the cubic press method. In this method, there are six anvils which provide pressure to a cube shaped volume.

The second method, devised by the Japanese, is known as Chemical Vapor Deposition (CVD) method. In this method, the necessary environment is created for carbon atoms in a gas to settle on a surface for the diamond crystals to grow.

Properties
Simulated diamonds have certain peculiar properties as compared to the typical properties of a natural diamond. They include:
These diamonds may either be made up of a single continuous crystal, or of several smaller crystals. The single crystal diamonds are used to make gemstones, while the smaller crystals are used in industrial applications.
The hardness of the diamonds made using the Chemical Vapor Deposition (CVD) method can be controlled depending upon their purpose. Artificial diamonds that are harder than natural diamonds can also be made.
No natural crystal is pure, because it can contain many different impurities. Natural diamonds are, therefore, flawed; whereas simulated gems appear flawless.
They usually give color to the crystals, and even add certain properties (depending upon the properties of the chemical which causes the impurity). Due to the processes used in the creation of artificial diamonds, there are chemicals which have to be used in the process. For example, nitrogen gives the diamond a yellowish color, while boron gives a bluish tinge.
Uses and Applications
Simulated diamonds are gaining a lot of popularity because of their affordable prices. Wedding jewelry sets made of colorful diamond simulants are also preferred by people all over the world. However, apart from jewelry making, they have varied applications and uses. Due to their hardness, diamonds have always been needed in machine tools. Due to cost and hardness factors, simulated diamonds are used on a wide scale in various cutting tools.

Synthetic diamonds have also found their uses in the electronics industry. Conductive diamonds are used as electrodes in several cases. Since diamonds are almost totally chemically inert, they are also used in the waste water treatment of organic effluents. Thus, simulated diamonds are soon becoming the norm for various types of industrial and technological applications in the world.

Additional Info on the History of Synthetic Diamonds

Similar to simulated diamonds, the history of synthetic diamonds also dates back to the eighteenth century. In 1797, it was first discovered that diamonds comprised pure carbon. Ever since then, attempts have been made by several people to produce diamonds synthetically. Many scientists tried to make synthetic diamonds using a variety of processes. Chief among them were Ferdinand Frederic Henri Moissan and Sir William Crookes. But no one met with much success. Eventually, in 1954 Howard Tracy Hall grew a synthetic diamond in a reproducible and verifiable process while he was working with General Electric. He even received a medal from the American Chemical Society for his work in 1972.

Lastly, it should be noted that although they look like diamonds, simulated diamonds are NOT actually diamonds. You can buy them if you are looking for inexpensive jewelry options. However, make sure that you do not end up paying excess for these artificial gems. Good luck
Read more at Buzzle: http://www.buzzle.com/articles/what-are-simulated-diamonds.html

4C Diamond:Clarity :ความสะอาด

4C Diamond:Clarity :ความสะอาดจากตำหนิภายในและภายนอกของเพชร ที่มองผ่านกล้อง10x และตาเปล่า

Internal Inclusion in diamond 3

Internal  Inclusion in diamond :Color Zoning

Inclusion in diamond-2

Internal  Inclusion in diamond

Inclusion in diamond-1

Inclusion in diamond

สิ่งที่ไม่มีเขียนระบุในใบเซอร์ ฯ

รู้หรือไม่  สิ่งที่ไม่มีเขียนระบุในใบเซอร์...ที่อาจทำให้เพชรราคาตกหรือพุ่งกระฉูด
..แต่ที่แน่ๆคนซื้อไปขายต่อได้กำไร
ตำหนิสีดำ หรือที่เรียกว่า "Black Pinpoint" แยกได้ 3 ระดับ
- B_PP เป็นจุดดำที่เล็กมากไม่สามารถมองเห็นได้ด้วยตาเปล่า....ต้องใช้กล้องกำลังขยาย 10 เท่าขึ้นไปถึงจะพบตำหนิดังกล่าว และจะพบได้ตั้งแต่คุณภาพ VVS2 ลงไป
- B1 เป็นจุดดำที่มีขนาดใหญ่กว่า B_PP อาจมองเห็นได้ด้วยตาเปล่าคำนวนแล้วประมาณ 20% ของเพชรที่มี B1 ซึ่งจะขึ้นอยู่กับระดับของคุณภาพของเพชร
-B2 เป็นจุดดำที่มีขนาดใหญ่กว่า B1 ซึ่งสามารถมองเห็นตำหนิดังกล่าวได้ด้วยตาเปล่า

ป.ล. 😉แต่ทั้งหมดก็เป็นตำหนิที่มาจากธรรมชาติ...ไม่ได้มาจากมนุษย์สร้างขึ้น...😤คนไทยถือเรื่องนี้แต่ก็มีร้านจำนวนไม่น้อยที่รับไปขาย...โดนเลือกให้มีตำหนิดังกล่าวที่ด้านข้างของเพชรเพื่อยากแก่การตรวจสอบตำหนิแทนที่หน้าเทเบิล...ซึ่งถือเป็นอีกทางเลือกที่ช่วยลูกค้าประหยัดงบประมาณได้เช่นกัน
 
เครดิต..  แอดมิน diamondbymanee

เพชรกลม 1.00 กะรัต น้ำ97 คุณภาพ VVS2

📢📢มาอีกแล้วค่า โปรโมชั่นเพชรสวยๆ 📢📢

🤑จากราคาปกติ " 342,000 บาท "
พิเศษสุดๆ เสนอขายในราคาเพียง “  260,000 บาท " 😉

💎เพชรกลม 1.00 กะรัต เพชรน้ำขาวใส เพชรน้ำ97   เนื้อเพชรสะอาด คุณภาพ VVS2 การเจียระไน ขัดเงาและความสมมาตร 3Excellent มาพร้อมกับ H&A = EX เพชรเม็ดนี้เล่นไฟระยิบระยับสวยสุดๆคร้า...สุดยอดแห่งความเพอร์เฟค มีใบรับรองจากสถาบันอัญมณีระดับโลก GIA 5181051857

ดร.สันต์ เจมส์ อะร่า
Gems Ara by Dr. Saint
0918078228

Diamond 1, 109carat

Source: Sotheby's

THE 1109-CARAT “LESEDI LA RONA”

One of the largest and oldest gem-quality diamonds ever discovered will be sold by Sotheby's in London next month.

The three million year old, 1,109 carat diamond was unearthed last November at Lucara Diamond Corporation's Karowe mine in Botswana, Africa.

Lucara is a member of the Lundin Group and is listed on the TSX Exchange, NASDAQ OMX First North Exchange and Botswana Stock Exchange. 

The Karowe mine produces less than one percent of the world's diamonds, but more than half of those mined stones are both Type IIA pure white and over hundred carats.

Dubbed "Lesedi la Rona," or "our light" in the Tswana language, this particular gem could sell in excess of $70 million dollars. Roughly the size of a tennis ball, It measures 66.4 x 55 x 42 mm. inches and is second in size only to the 3,016 carat "Cullinan" diamond mined in South Africa in 1905 and produced nine diamonds which are part of the historic Crown Jewels of the United Kingdom,

David Bennett, chairman of Sotheby's jewelry division, called the unprecedented discovery a "find of a lifetime" 

"Not only is the rough superlative in size and quality, but no rough even remotely of this scale has ever been offered before at public auction," said Bennett.

Because of its "exceptional" transparency, the stone, when cut and polished, could yield the biggest high quality diamond in history.

According to a study by the Gemological Institute of America, Lesedi La Rona is part of a rare subgroup which comprises two percent of all gem diamonds considered the most chemically pure. 

The largest existing diamond sale was set last year when Hong Kong industrialist Joseph Lau paid $46.5 million for a 12.08 carat polished blue diamond. According to Sotheby's, which handled the sale. the "Blue Moon" diamond was a gift for Lau's seven year old daughter.

Sotheby's will auction the Lesedila Rona on June 29 in London.

Kerima GreeneSenior Talent Producer, "Power Lunch"
Cr.: http://www.cnbc.com/2016/05/04/70-million-1109-carat-diamond-heads-to-auction.html

Certification HRD

More about certification

Maintaining a transparent, international standard

The Diamond Lab of HRD Antwerp was founded in 1976 to meet the growing demand for reliable diamond certificates or grading reports. It's the largest diamond lab in the world to conform to the rules for grading polished diamonds set by the International Diamond Council (IDC). These rules have been approved by the World Federation of Diamond Bourses (WFDB) and the International Diamond Manufacturers Association (IDMA), the industry's two leading representative bodies.

Strict anonymity and objectivity 

The absolute objectivity of the grading results is guaranteed by means of a double coding system: one set of codes is given to the owner, while the other follows the diamond in the lab. Strict anonymity guarantees strict objectivity.

Quality that inspires confidence

The integrity of the grading process is absolute. The Diamond Lab applies an uncompromising operating code which it supports by using some of the most sophisticated technology and qualified graders that work in the trade. It is constantly kept up-to-date on the latest developments and innovations in the profession by HRD Antwerp's extensive in-house Research department.

The results of the examinations performed are based on scientific methods and observations made in the Diamond Lab and in the labs of its partnering universities.

The 4 C's of diamond 

The quality of a diamond is defined by means of the 4 Cs: carat, colour, clarity and cut. These four characteristics determine your diamond's value. And, as every diamond is unique, they are also very useful for identification. 

Carat

The weight of a diamond is expressed in carats. One carat equals 0.2 grams or 100 points. Each diamond is weighed immediately upon receipt at the reception desk. HRD Antwerp has extremely accurate scales that measure up to 1/100,000 of a gram. This accurate weight is very useful for the identification of the diamond 

Colour

Most diamonds range in colour from white to slightly yellow. However, diamonds can occur in all sorts of colours ranging from brownish to striking yellow, pink, purple, red and blue. These are called 'fancy colours'

Clarity 

All diamonds have traces of their growth history. The clarity scale reflects the size, number, location and visibility of the internal characteristics when examined with a 10x loupe.

Cut

A diamond's cut is essential to its beauty. If the diamond is not well-cut, the diamond will not interact with light as it should. Even a diamond with outstanding colour and clarity will not display the fire and brilliance that diamonds are famous for.

Since January 2009, HRD Antwerp has refined its cut grade, and now grades the diamond's proportions, polish and symmetry. The polish describes the finish of the facets, while the proportions determine the brilliancy and the fire of the diamond. The symmetry describes the variations of the different parameters that define the proportions. Each grade is divided into 4 categories: Excellent, Very Good, Good and Fair.

Cr. https://my.hrdantwerp.com/index.php?id=42

Heart and Arrow diamond grading

H&A

Hearts and Arrows

EVALUATION & GRADING TOOLSHEARTS AND ARROWS VIEWER
Cr. http://shop.diamondideals.com/education/find/evaluation.cfm

Hearts and Arrows is a visual phenomenon that appears in the finest Ideal Cut round brilliant diamonds when viewed in a Hearts and Arrows viewer or gemscope. Diamonds cut with precisely aligned and carefully shaped facets combined with optimum proportions produce an incredibly brilliant sight, called Hearts and Arrows.

The viewer is merciless when it comes to any deviation from perfection. Any detour from the correct path of light will result in the deformation or absence of either the hearts or the arrows. This device, as unassuming as it may appear can clearly show even the untrained eye how well or how poorly a diamond is cut.

Diamond Ideals will give you (FOR FREE) a Hearts and Arrows viewer with every purchase of a Hearts & Arrows diamond larger than 1.0 carats.

OGI MEGASCOPE AND SARIN

The OGI Megascope and Sarin are high-tech, Electro-optical device used to analyze the cut parameters of precious stones. The software associated with this high-tech device makes several types of analyzing functions available. The technology has the capability of analyzing each and every facet as well as the diamond's diameter, crown angle and height, pavilion angle and depth, culet size, culet placement, table size, table placement, table depth, girdle thickness and other relevant characteristics.

Please note, these analytical devices have a measurement accuracy of 0.2° for the crown and pavilion angle, 0.3% for the table and 0.015 mm for the diameter. Therefore, results may vary slightly between machines. We consider the AGS and GIA grading reports to be the authority when analyzing proportions. With the introduction of the AGSL’s performance based grading as well as the GIA cut grade with specific data on their reports, we find the information provided by OGI and Sarin fairly irrelevant unless you are re-cutting a stone.

IDEALSCOPE

The IdealScope is a red reflector device that helps visualize the cut quality and performance of diamonds. This little device shows you areas of light leakage in diamonds you are considering for purchase. Light leakage can be seen as areas of pure white within and around the diamond. It is important to note that all diamonds have some leakage, particularly under the table and around the diamond's edge. This minor leakage is seen as pale red areas or small white wedges near the edge of the diamond. What is important is to notice the presence or absence of large white spots in the IdealScope image. Large white areas are an indication of significant light leakage.

The pictures are not taken with scientific accuracy but are set up manually, leaving room for small optical inconsistencies.

Below is an IdealScope chart depicting the difference between excellent and poor performing diamonds.

WHAT IS A SUPER IDEAL DIAMOND?

WHAT IS A SUPER IDEAL DIAMOND?
Cr. http://shop.diamondideals.com/education/ideal_diamond.cfm

I·de·al n. 1. A conception of something in its absolute perfection. 2. One that is regarded as a standard or model of perfection or excellence.

An Ideally proportioned stone will have tremendous brilliance and scintillation. An ideally cut diamond will not be cut to retain weight or appear larger than it is. The only goal in cutting an ideal cut diamond is to maximize the brilliance, fire, sparkle and beauty of the diamond.

Of the many independent labs available, only the American Gem Society Lab and GIA grade diamonds for the accuracy of their cut. Many labs claim there is no range of proportions that are more brilliant than others or make their parameters so loose that just about any diamond can be called Ideal.

At Diamond Ideals, we trust only the AGS Lab and GIA to grade our diamonds. An AGS Diamond Quality Document (DQD), showing the stone to have achieved Ideal specifications for Polish, Symmetry, Proportion and Light Performance (in the new AGSL documents) or a GIA grading report showing Excellent polish, symmetry and cut accompanies every Diamond Ideals ideal cut diamond. Every loose diamond we sell is accompanied by a grading report.

Every facet in an Ideal Cut diamond must be placed at precise angles and has precise proportions. This ensures an Ideal balance between maximum brilliance and dispersion of light. Any discrepancy from these proportions will disrupt the even distribution and dispersion of light within the stone, and will result in a loss of beauty.

WHY AREN'T ALL DIAMONDS CUT TO IDEAL PROPORTIONS?

The answer is one of simple economics. It takes longer and more technology to cut an Ideal Cut. The process is assisted by computer and laser analysis. Only very experienced cutters can achieve this level of excellence, and, unfortunately, there is a greater weight loss of the original rough diamond. All of these factors contribute to the rarity and cost of Ideal Cut diamonds.

CAN THERE BE "GIA IDEAL CUTS"?

Although the GIA specifically claims that there are no sets of proportions that are "Ideal" Diamond Ideals obviously disagrees. Finding a GIA triple excellent and using a Hearts & Arrows scope can considerably narrow the field. Also insist on seeing pictures of the diamonds to make sure you are getting a great performing diamond.

ความรู้เกี่ยวกับเพชร การตรวจเช็คและระบุตำหนิภายใน ภายนอกของเพชร

DIAMOND PLOT

Because a photograph cannot capture the subtleties of clarity, GIA uses a diamond plot to map a diamond's interior and exterior flaws. A diamond plot is a graphic representation of every flaw that affects the overall clarity grade. The flaws are found under 10x magnification by a skilled grader.

 
Example GIA Diamond Plot: The Key To Symbols section
shows the flaws in order of severity

While the plot shows the type and position of each flaw, the actual visibility of the flaw is communicated in the diamond Clarity Grade itself (i.e. two diamonds may have very similar plots, but very different Clarity grades, reflecting the actual severity and visibility of the recorded flaws).

Besides the plot, there is also a comment section on the certificate where additional clarity characteristics are often noted. These are usually too minor to be reflected in the plot itself. Between the plot and the comment section, all inclusions visible under 10x magnification are accounted for.

http://www.lumeradiamonds.com/glossary/GIA_Grading_Report

ความรู้เกี่ยวกับเพชร สอนทำแหวนเพชร

DIAMOND ANATOMYTHE

BASIC PARTS OF A CUT DIAMOND

Table: The flat facet on the top of the diamond. It is the largest facet on a cut diamond.

Crown: The upper part of the diamond above the girdle. Consists of a large flat area on top called a table, and several facets below it

Girdle: The outer edge or the widest part of the diamond forming a band around the stone.

Pavilion: The bottom part of the Diamond, below the girdle.

Culet: A tiny flat facet that diamond cutters sometimes add at the bottom of a diamond's pavilion. Its purpose is to protect the tip of the pavilion from being chipped or damaged. Once a diamond is set in jewelry, though, the setting itself generally provides the pavilion with sufficient protection from impact or wear. Large or extremely large culets were common in diamonds cut in the early part of this century, such as the Old European or Old Mine Cut. However, such large culets are rarely seen today. Most modern shapes have either no culet at all, or a small or very small culet.

Depth: The height of a diamond from the culet to the table. The depth is measured in millimeters.

Crown angle: The angle at which a diamond's bezel facets intersect the girdle plane. This gentle slope of the facets that surround the table is what helps to create the dispersion, or fire, in a diamond. White light entering at the different angles in broken up into its spectral hues, creating a beautiful play of color inside the diamond. The crown angle also helps to enhance the brilliance of a diamond.

Table percentage: The value which represents how the diameter of the table facet compares to the diameter of the entire diamond. So, a diamond with a 60% table has a table which is 60% as wide as the diamond's outline. For a round diamond, gemologists calculate table percentage by dividing the diameter of the table, which is measured in millimeters (this millimeter measurement does not appear on diamond grading reports) by the average girdle diameter. For a fancy shape diamond, table percentage is calculated by dividing the width of the table, at the widest part of the diamond, by the millimeter width of the entire stone.

Facet: The smooth, flat faces on the surface of a diamond. They allow light to both enter a diamond and reflect off its surface at different angles, creating the wonderful play of color and light for which diamonds are famous. The table below shows all the facets on a round brilliant cut diamond. A round brilliant has 58 facets (or 57 if there is no culet).

Symmetry: Refers to variations in a diamond's symmetry. The small variations can include misalignment of facets or facets that fail to point correctly to the girdle. Symmetry is regarded as an indicator of the quality of as diamond's cut; it is graded as either Ideal, Excellent, Very Good, Good, Fair or Poor.

Fluorescence: An effect that is seen in some gem-quality diamonds when they are exposed to long-wave ultraviolet light (such as the lighting frequently seen in night clubs). Under most lighting conditions, this fluorescence is not detectable to the eye. However, if a diamond is naturally fluorescent, it will emit a soft colored glow when held under an ultraviolet lamp or "black light." Fluorescence is not dangerous to the diamond or to the wearer; it is a unique and fascinating quality that occurs naturally in a number of gems and minerals. Most commonly diamonds fluoresce blue, but can also fluoresce yellow or white depending on which trace elements are found in the matrix of the diamond crystal. Fluorescence is described as none (or inert), faint, negligible, medium, strong and very strong.

Fluorescence in diamonds can have both favorable and undesirable effects. For example, diamonds in the color range of I to N with medium to strong blue fluorescence can appear more colorless, which is an obvious advantage. The blue acts to mask or offset the very faint body color of these diamonds. On the other hand, diamonds with very strong fluorescence can exhibit an oily or milky appearance, even under incandescent lighting. However, according to a GIA study, the average observer could not detect any difference in color or transparency when viewing diamonds with fluorescence.
http://www.diamondideals.com/education/find/anatomy.cfm

การรับออร์เดอร์แหวนเพชร-2

ข้อควรปฏิบัติ   การรับสั่งทำแหวนเพชร

ขั้นตอน การรับสั่งทำแหวนเพชร รับออเดอร์ -1

ข้อควรปฏิบัติ   การรับสั่งทำแหวนเพชร

Diamond Grading: The 4 C's: cutting

Diamond Grading: The 4 C's

The 4 C's, when referring to diamond value, are color, clarity, carat weight and cut. All four factors are equally important in determining the final cost of a diamond. The criteria for diamond grading, most respected internationally, was developed by the Gemological Institute of America (the G.I.A.). The terminology and systems described on this page, are those of the G.I.A.

Following, is an explanation of these terms.

Cutting.

At the turn of the last century, it was mathematically determined, what the optimal proportions for a diamond should be to assure maximum brilliance and dispersion. Those proportions are as follows:

The quality of a diamond's cut makes all the difference in how the stone appears. A poorly cut "D", Flawless stone, can look dead and lifeless, whereas an ideally proportioned diamond of much lower color and clarity will appear radiant and dazzling. So, why aren't all diamonds ideally proportioned? The answer is quite simple. Diamonds are sold by weight. Stones cut to ideal proportions waste more of the diamond crystal, therefore weigh less than stones that are cut to maximize weight.

Diamond Grading: The 4 C's: carat weights

Diamond Grading: The 4 C's

The 4 C's, when referring to diamond value, are color, clarity, carat weight and cut. All four factors are equally important in determining the final cost of a diamond. The criteria for diamond grading, most respected internationally, was developed by the Gemological Institute of America (the G.I.A.). The terminology and systems described on this page, are those of the G.I.A.

Following, is an explanation of these terms.

Carat Weight

Carat is a unit of weight, not size. There are 5 carats in a gram. The weight of a diamond is measured in carats. A carat is divided into 100 parts, called points.

1   carat =1.00 carat=100points
1/2 carat= 0.50 carat= 50 points
1/4 carat=0.25 carat= 25 points

Credit: http://gemologyonline.com/diamondgrading.html

Diamond Grading: The 4 C's : clarity

Diamond Grading: The 4 C's

The 4 C's, when referring to diamond value, are color, clarity, carat weight and cut. All four factors are equally important in determining the final cost of a diamond. The criteria for diamond grading, most respected internationally, was developed by the Gemological Institute of America (the G.I.A.). The terminology and systems described on this page, are those of the G.I.A.

Following, is an explanation of these terms.

Clarity

Practically all diamonds contain naturally occurring internal characteristics called inclusions. The size, nature, location and amount of inclusions determine a stone's clarity grade and affect its cost. Clarity is determined using 10X magnification. By definition, if something is not visible at 10X, it does not effect the clarity.

FlawlessVVS1VVS2VS1VS2SI1SI2I1I2I3

1.Flawless/Internally Flawless= No inclusions visible, by an expert at 10X magnification
2.VVS1-VVS2= Very, Very slight inclusions very difficult for an expert to find under 10X
3.VS1-VS2= Very slight inclusions difficult for an expert to find under 10X
4.SI1-SI2= Noticeable, relatively easy to find under 10X. Not visible w/o magnification in a face-up direction.I1-I3= Obvious under 10X, may be visible to the unaided eye, I3's inclusions may effect the stone's durability.

Credit: http://gemologyonline.com/diamondgrading.html

Diamond grading :color

Diamond grading for  lerning.

Diamond Grading: The 4 C's

The 4 C's, when referring to diamond value, are color, clarity, carat weight and cut. All four factors are equally important in determining the final cost of a diamond. The criteria for diamond grading, most respected internationally, was developed by the Gemological Institute of America (the G.I.A.). The terminology and systems described on this page, are those of the G.I.A.

Following, is an explanation of these terms.

Color

The color of a diamond refers to the relative amount of yellow, brown or gray body color that a stone possesses. The G.I.A. scale starts at "D" and goes through "Z", with "D" being void of any body color, and "Z" having a light yellow, brown or gray color.

Cradit: http://gemologyonline.com/diamondgrading.html