How to treat one of the diamond appraisal certificates?

GIA certificate

The value of a diamond depends on its four C's. Some people call the diamond appraisal certificate the fifth C of diamonds. In fact, according to the name marked by the American Gemological Institute, it is "diamond classification report" or other unrealistic names. Today, the diamond classification system and terminology established by Gemological Institute of the United States have long been recognized by the public as the international diamond language, and many appraisers who use other systems also cite its terminology. There are many practitioners in cash gem appraisal offices. Although not all of them graduated from Gemological Institute of the United States, the diamond appraisal standard used is still based on the system established by GTL, because no other system can replace extensive public recognition.

The origin of diamond appraisal certificate

Gemological Institute of America (GIA) was established in Los Angeles on 19 13. At first, it trained jewelers how to evaluate prices through evening classes and correspondence courses, and provided reference materials for wholesale prices of jewelry. But before evaluating the price, we must first determine the quality. In order to meet the needs of facts, GIA has established its own system to evaluate the quality of diamonds and other precious stones.

After World War II, new york's position in the diamond market became more and more important. More and more jewelers asked GIA how to determine the quality of diamonds, so that after 1953, GIA set up its first appraisal office in new york and began to issue diamond certificate reports, commonly known as appraisal certificates, to meet the demand. In addition to the inspection office in new york, two other inspection offices have been established in Santa Monica, California and downtown Los Angeles (now the Los Angeles inspection office has been built), so there are mainly two inspection offices. The official name of these appraisal institutions is "GEM TRADE LABORATOR, Inc.", which belongs to GIA and only appraises gems, but does not.

GIA is a non-profit organization established with the support of famous American jewelers and celebrities. Therefore, GIA is an appraisal research institution enjoyed by American jewelers, and its subsidiaries, such as GTL, provide appraisal services for jewelers, which is widely trusted by all walks of life and is not discriminated against because of the support of American jewelers.

The appearance of diamond identification certificate has greatly changed the diamond trading. In the past, it was necessary to identify the quality one by one, but now you can refer to the identification certificate. According to GTL's statement, GTL is not responsible for the certificate issued by GTL if it is used as the basis for trading. However, because its certificate is widely welcomed and trusted, many jewelers are happy to use it as the basis of diamond quality. The circulation of certificates was originally only between diamond dealers and finally reached consumers. It is popular not only in America, but also all over the world. Therefore, the demand for certificates is increasing, and the demand exceeds the supply, which has formed the bottleneck of diamond trading.

Function and function of diamond appraisal certificate

The real significance of diamond grading report is diamond quality grading report. GIA has repeatedly stated that it is a report, not a certificate. The main purposes of this report are:

Distinguish between true and false: Anyone who has a diamond identification certificate is obviously a diamond, not another kind of gem or diamond counterfeit.

Characteristic record: The weight, size and fluorescence reaction recorded in the appraisal book are all characteristics of identifying diamonds. In particular, the characteristic inclusions of diamonds drawn in the attached drawings are a clear identification mark. If you don't draw the surface features or inclusions of the diamond and explain the diamond identification certificate, this function will be gone.

Quality analysis: the weight, color, clarity, grinding (commonly known as lathe worker) and proportion of diamonds are all stipulated in the appraisal certificate, so the appraisal certificate is the analysis record of diamond quality.

Valuation reference: before a diamond is valued correctly, it is necessary to know its quality first. Most of the information about quality in the appraisal certificate is explained, so the appraisal certificate is an important reference document for the value of ancient diamonds.

Retained materials: All the materials recorded in the certificate are very clear reference materials for future re-evaluation, procurement cost analysis and sales statistics.

First, shape and grinding (shape &; Cutting style)

The shape of a diamond refers to its correct contour, that is, the shape of its waist, such as circle, olive, square and so on. Diamond cutting is the first C of diamond 4C. Due to the different shapes, numbers and arrangements of facets, diamond cutting has various forms, such as brilliant, stepped, mixed, etc.

There are many kinds of cutting and grinding forms of diamonds, but the most common form is full-cut BRILLIANT, usually called BRILLIANT, which has 58 facets, that is, 33 facets at the crown and 25 facets at the bottom (including pointed bottom, or 24 facets at the bottom if there are no facets), and the most common shape is round, that is, round brilliant.

All other shapes or forms of cutting and grinding except round and bright are collectively called fancy cutting. Fancy cutting and grinding is just a general term, which can be divided into the following three categories if further classified: first, round bright varieties: olive bright, pear bright, oval bright, heart-shaped bright and so on; Secondly, it is a square cut by emeralds: it includes all kinds of square diamond shapes, such as horse's head, fish, butterfly, tennis racket, cross, triangle, half moon, head portrait and so on. , all kinds of strange things.

Two other nouns are also usually recorded in the shape and grinding column:

1. Combined or mixed cutting: one form at the top and another form at the bottom.

2. Trimming scissors: people who make slight changes on the basis of a certain type.

The so-called brilliant cutting means that the facets are arranged radially, just like the sun and the moon.

The light of the stars radiates outward. For example, the crown is bright, the center is the desktop, and there are usually eight kite faces, eight star faces and sixteen waist faces around it. The bottom is usually centered on the bottom tip, and the facets radiate outward like light.

The so-called step cutting, that is, emerald cutting, means that facets are arranged in layers, one by one from the center to the outside. Hybrid cutting mill is a stepped cutting mill combined with bright cutting mill.

The narrative method of modeling and cutting and grinding is to write modeling first, then cutting and grinding style. E.g., a round diamond is correctly described as a round brilliant cut); If the top and bottom are bright; The same diamond, if the crown is bright and the bottom is stepped, is written as a circular mixed cut.

Second, the size (measurements)

The measured diamond size is measured in millimeters (or abbreviated as mm, usually abbreviated), and recorded to the second decimal place below millimeters. Because the position of each measurement may not be exactly the same, there will be slight errors when using different gem measuring calipers. If there are two different certificates for the same diamond, the size will be slightly different, and the results of the second measurement before and after will be different, but the limit will not exceed 0.02 mm

Under the precise measurement of decimeter calipers, round diamonds are not pure circles, so the minimum and maximum diameters and the total depth are recorded, while colored diamond records its length, width and height, so there are three size figures.

Three. weight

The weight is measured in metric carats, which is the second c of diamond 4C, and each carat is equal to 200mg. Or 0.2 grams, so 1 gram equals 5 carats. The weight of a diamond is accurate to the second decimal place below carat, and the third decimal place can be rounded off or omitted according to the situation. The second place after the decimal point is "point", and each carat is equal to 100 point.

In the Middle East, there is a kind of Sophora japonica whose seeds are the same weight and size. The English name of this tree is CAROB TREE, which is quite common in the local area. In ancient times, pearl merchants first used their own seeds as the weight unit of pearls, that is, carats, that is, carats as the source of weight units. Carat has been widely used as a unit of weight for precious stones. At first, the carat weight in different areas was slightly different. However, since 19 13, the United States has stipulated that each carat is equal to 200 mg, and all advanced countries take this as the standard, so there is no competition.

Four. Percentage of full depth (depth%)

The cutting and grinding ratio of diamonds mainly includes the following items. The waist width (average width of round diamonds) is based on 1 or 100%: (1) full depth percentage (depth %)(2) desktop percentage (table%) and (3). (4) base size and surface modification, (5) polishing or polishing, and (6) symmetry.

The percentage of the full depth of a round diamond is a number obtained by dividing the full depth (thickness) by the average of the minimum diameter and the maximum diameter, and then converting it into a percentage, in other words, it is the percentage of the thickness and diameter of the diamond. The percentage of full depth is calculated to the first decimal place, and the second decimal place is rounded off.

For example: round drill: diameter 6.50-6.59, thickness 3.83→ (6.50+6.59)/2=6.545=6.55 (rounded corner), 8.83/6.55=0.5847=58.5%= full depth percentage.

Colored diamond is obtained by dividing the height (full depth) by the width, regardless of the length.

For example, colored diamond: length 13. 18, width 8.24, height 5.45 → 5.45/8.24 = 0.6614 = 66.1%= full depth percentage.

The main purpose of recording the percentage of full depth is only to know the approximate thickness of the diamond. The greater the percentage, the thicker the diamond and the smaller the diamond. However, the total depth of a diamond is deeply influenced by the surface size, crown height, waist thickness and bottom depth, especially the surface size changes the most. When the table is large, the crown is thin, resulting in a small percentage of the total depth and a large percentage of the total depth. The ideal crown angle should be 341/2 and the base depth should be 43. 1%. However, according to the actual observation experience, if the crown angle is within the range of 32 to 36 and the bottom depth is between 42.5% and 45.5%, the diamond can show its own brilliance, but from a specific position, it is not the case due to various reasons.

Verb (abbreviation for verb) Desktop percentage (table%)

Divide the length of the longest diagonal of the round diamond table by the average diameter, and then divide the table width by the diamond width of colored diamond, and the percentage is the table percentage. The desktop percentage is calculated as an integer, and the decimal point is rounded off. For the desktop, the most obvious influence on the size of the desktop is the thickness of the crown. Besides the crown thickness, the desktop size is also affected by the crown thickness. If the crown keeps a certain thickness, the larger the crown angle, the larger the desktop, and the smaller the crown angle, the smaller the desktop. In modern diamond cutting and grinding theory, the most controversial issue is the size of the desktop, and there is no absolute standard so far. The ideal crown angle is 341/2, and the most common desktop is 58% to 65%. Desktops that are too small or too big are generally disliked.

According to the current recommendations of Gemological Institute of the United States on the classification of diamond cutting and grinding, the desktop can be divided into the following four types according to its size:

Small desktop: 53% to 60%

Medium desktop: 6 1% to 64%

Large desktops: 65% to 70%

Oversized desktop: 7 1% or above.

The influence of desktop size on light, fire and appearance size;

The desktop is smaller and the desktop is bigger.

Light is denser (less perceived) and more diffuse (more perceived).

More fire and less.

The appearance size is getting smaller and smaller.

Six, waist circumference (waist seal)

The waist bar on the diamond appraisal certificate includes the following two items:

(1) thickness: the thickness of important positions can be divided into the following eight situations:

1. Extremely thin is extremely thin.

2. Very thin-not bad

3. Thin

4. Medium is moderate

5. A little thicker is a little thicker.

6. Thick-fair

7. Very thick

8. Very thick

The waistline has a thickness, which is used to facilitate inlay and prevent the diamond from being fragile because it is thin. The weak waistline is certainly not as strong as the thick waistline in cracking resistance. But the waist line only needs a little thickness, which is strong enough. Too thick waistline makes the diamond retain unrealistic weight and makes the diamond look thick and small, so too thick or too thin waistline is not a good waistline.

Of course, the thickness of the waistline is moderate, but the finished diamond is cut and polished from the original stone crystal of the diamond, and the shape of the natural crystal is inevitably uneven and ideal, so the waistline actually seen is often uneven. For example, if it is as thin as S 1. The thickness is recorded under the waistline of the appraisal book, which means that some waistlines are thin, moderate and slightly thick, the narrowest part is thin and the widest part is slightly thick. The thickness of the cloth is not necessarily uniform, sometimes the thickness of the thin part is more than that of the thin part, and sometimes the thickness is more than that of the thin part.

The thickness distribution should be even and gradual. If the thickness suddenly becomes thinner, the waistline will appear uneven and wavy, which should be regarded as one of the symmetry defects. The more steps the waist spans, the more uneven it is, and the worse it is. The wavy waistline indicates that the angles of the bottom facets are inconsistent, or there are larger natural rough surfaces or redundant facets under the waistline. GIA system records the thickness of waist circumference by visual inspection, but does not actually measure its percentage, so it usually uses the above eight situations to describe the thickness without recording its percentage.

(2) the smoothness of the belt:

In addition to polished or faceted waistlines, normal waistlines should be as translucent as white fog and have a very smooth surface. If you are too careless or sloppy when grinding, it will be rough and become a rough waist seal.

Polishing waist record: polishing. Faceted waistline is recorded as faceted. A thin, polished or faceted waistline should be regarded as a good waistline, and only a rough waistline can be regarded as one of the defects of cutting and polishing, which slightly impairs the beauty of diamonds.

If there is a beard crack on the waistline, use a belt with beard or feathers to circle the city. Stripes are usually not marked on the attached drawings, but only recorded in the remarks column. According to GIA system, IF there are obvious cracks in the waist, the clarity grade of diamonds is classified as purity grade (FL) or internal purity grade (IF).

Seven, pointed bottom (CULET)

Among the 58 bright faces, the sharp face is also considered as one side, and the size is as follows:

1. Pointed or none.

2. Very small is very small.

3. Small is small

4. Medium and medium. Nbspbsp is medium.

5. A little bigger is a little bigger.

6. Big ones

7. Very big, very big

8. Very big

The size of the sharp bottom has no obvious influence on the brilliance and value of diamonds, and the normal sharp bottom should be small or medium. The bottom surface without sharp points is easy to make the surface tip collapse. At present, the oversized pointed bottom is rare. Although it doesn't look good, it can be corrected if the bottom is polished a little and only a small weight is lost.

A sharp bottom that is unpolished, rough or looks like a small white dot is usually called rough, and a worn or broken sharp bottom is called wear or chipping. These two abnormal tips should be reground, but they are not serious defects.

Eight, finish, polish and symmetry.

Polishing refers to the degree to which each facet on the diamond surface is polished finely, and mainly judges whether there are obvious wheel marks or burn marks. Strictly speaking, the analysis of diamond symmetry should be divided into two categories: one is serious or significant symmetry defects, which should be considered within the ratio range and explained in the remarks column. Second, slight or minor asymmetry refers to whether the shape and arrangement of facets are neat or appropriate, which should be listed as decoration scope, and only the superior and inferior grades are comprehensively judged and recorded in the symmetry column.

Analysis of the advantages and disadvantages of polishing and symmetry is usually based on the following five levels:

Excellent, excellent

Very good very good

Very good very good

Fairness is fairness.

Poor; poor

Of all the precious stones, the most polished and symmetrical one should be the diamond. Severe polishing or poor symmetry are only exceptions, which are very rare. If you can find fashion, you should explain it in the remarks column. The quality of diamond cutting and grinding depends not only on the polishing and symmetry of the "decoration" column, but also on whether the cutting and grinding ratio and angle of the whole diamond are appropriate. In fact, polishing and symmetry affect the value of diamonds, each limited to a small percentage. It is usually around 1~2%, and rarely reaches 3%, because poor grinding or symmetry can be corrected by re-grinding or slightly trimming, but the proportion or angle is not up to standard and it is difficult to modify. If it is modified, the weight loss will be more, so it will have a great influence on the quality of diamond cutting and grinding.

Nine. Transparency level

This is the third C of diamond 4C, and the division of clarity grade is magnified ten times.

Taking observation as the standard, the fine surface features or inclusions that cannot be detected under ten times magnification will not affect the determination of clarity grade, but it must be noted that GIA system uses binocular gemstone microscope as a tool to determine clarity grade, and finally uses hand-held ten times magnifying glass for re-inspection.

In all diamond appraisal projects, the most subjective one should be the clarity grade. Because no two diamonds have exactly the same surface features or inclusions. We must rely on the experience of appraisers to judge and determine their grades. Therefore, it is best to entrust a very experienced appraiser to judge the clear level of twelve people, to avoid one person's arbitrariness, and it is best to be audited by another irrelevant and uninformed person, so as to reduce the deviation caused by excessive subjectivity. For example, in GTL, two people will judge the clarity level, and IF the FL or IF level or the two initial nuclear opinions are different, it will be reviewed by a third party.

Because diamonds that meet the requirements of purity grade are very rare, the internal purity grade is the highest purity grade in general diamond trading (commonly known as the United States). Clarity is a description of the characteristics contained inside or outside a diamond. GIA does not encourage it to be called a defect because it has a negative meaning. Because of its ultra-small inclusiveness, VVS is easily misunderstood as all Americans. For example, the inclusion of VS grade does not affect the beauty and durability of diamonds.

Legend of clarity grade

When judging the clarity grade and looking at the characteristics, we need to consider all the characteristics inside and outside the diamond as a whole, including size, quantity, location, nature, color and whether it suddenly appears, and secondly, the impact on the durability of the diamond. Under the observation of ten times magnification, after finding the most obvious flaw, the definition level can often be judged, and other sporadic and inconspicuous small flaws rarely affect the judgment of the definition level. Therefore, the most important thing to judge the cleanliness level is the visibility of features, not the number of certificates on the drawing.

Micro surface features (defects, such as natural rough surface, extra facets, grinding wheel lines, scratches, wear marks, wounds, scars, etc.). ) does not affect other grades, except the distinction between purity grade and internal purity grade. For this tiny surface feature, except for the natural rough surface and extra facets, GTL is not marked on the internal drawing of the certificate, and only the tiny details about polishing (polishing) are not shown in the attached drawings, but the working drawing of its internal operation is described in detail. However, some inexperienced appraisers mistook these surface features for inclusions, so that the internal purity grade was misjudged as VVS 1. Also, the internal and external features that can only be seen when magnified more than ten times should be ignored and need not be marked on the drawing.

X. color grading

This is the fourth C of diamond 4C. Most colored diamonds belong to the yellow series. Diamonds of other colors are scarce, and when their colors are obvious, they all belong to the range of colored diamonds, so the classification of diamond fineness grade is limited to diamonds containing yellow.

Among all the color grading systems in the world, the grading system is the most detailed and practical, and it is the first to popularize the color grading system established by GIA. Today, its system has become the most famous diamond fineness grading standard in the world. Many countries or regions adjust their own systems with reference to this standard, or directly refer to the grade names of this grading system.

The color grading system of American Gemological Institute uses English letters to represent color grades, and D is the highest color grade, not A, B, C ... Each English letter represents the fineness range of each grade, not the specific fineness position. Only the standard fineness diamonds of each grade must be located at the highest fineness position of that grade. Therefore, although the internationally accepted diamond appraisal certificate lists diamonds of the same color, sometimes there are subtle differences between the upper and lower grades.

DEF is colorless in the third grade. No matter before or after observation, there is no contrast, it is colorless. GHIJ grade IV is colorless at first glance when viewed from the front, while KLM grade III is only slightly yellow when viewed from the front. Most people below level N will see its yellowish hue, so Z is the lowest color level. When the concentration of yellow exceeds Z level, it is colored as yellow, which can be divided into three levels according to its shade: fancy light yellow, fancy yellow and fancy thick yellow. Other kinds of colored diamond are also divided into these three grades.

Classification of fineness grades (GIA system)

According to the GIA system, each English letter represents the color range of the grade, not the specific position, and only the standard color diamonds must be located in the highest color position of the grade. For example, a graded diamond is higher than the standard color diamond E, that is, it belongs to the D grade; if it is higher than F, it is the E grade; if it is higher than G, it is the F grade; in other words, it is the G grade between standard stones G and H, the H grade between standard stones H and I, the I grade between standard stones I and J, and so on.

Color-the origin of the name

The name fineness is named after the gold content of gold. The less magazines gold contains, the more gold it contains and the higher its fineness. Diamonds contain yellow, just as magazines contain gold. The less yellow, the higher the color.

Correct understanding of color grading

As early as the1940s, American Gemological Institute invented the colorimeter. Although the instrument was improved later, its performance is still limited, and it is not universally applicable to any diamond. The main reason is that the factors affecting fineness are not fully understood. Moreover, the fineness of diamond is affected by cutting and grinding ratio, fluorescence reaction, transparency, color spots and other factors. Therefore, the Gemological Institute of the United States still uses real diamonds as the standard color diamonds to distinguish the colors of all levels. At the same time, it seems that it is still far away for the instrument to enter the universal practical stage.

At present, if GIA system is used as the grading standard of diamond fineness in gem appraisal rooms all over the world, then a set of main color diamonds (or main diamonds) that have passed GIA appraisal must be prepared, otherwise, the grading of fineness will not be completely consistent with its system, resulting in the phenomenon of losing the standard if it is too high or too low. In recent years, artificial cubic zirconia (CZ for short) has been used to replace real diamonds as standard diamonds, but the American Gemological Institute does not approve this method, mainly because the yellow color of (1)CZ is slightly different from normal diamonds, just like brown or gray diamonds are difficult to compare with yellow diamonds. (2) The flame (dispersive light) of 2)CZ is stronger than that of diamond, which will affect the accuracy of color judgment. (3) The color stability of 3)CZ is not good. After a period of time, the fineness grade naturally changes. Therefore, American Gemological Institute refused to identify CZ as a standard color diamond.

XI。 Fluorescence reaction

Fluorescence reaction refers to the color light produced when diamonds are stimulated by external energy, usually under ultraviolet radiation. According to its strength, it can be divided into five grades: (1) none, (2) faint, (3) moderate, (4) strong and (5) very strong. Weak does not record its fluorescence reaction color.

Fluorescence reaction is only one of the items detected by diamond identification certificate, and the intensity and color of records rarely affect the value of diamonds. For example, if the fluorescence reaction is blue or yellow, it does not mean that the diamond itself is blue or yellow. The fineness of the diamond is judged by its own yellow depth, not by the fluorescence reaction color.

Fluorescence reaction

Some diamonds can emit fluorescence under ultraviolet irradiation, with different luminosity, and most of them emit blue fluorescence. Figures (a) and (b) are the same batch of diamonds. Figure (a) shows their appearance under ordinary light, and figure (b) shows the fluorescence reaction of these diamonds under ultraviolet radiation. These diamonds are deliberately selected to have fluorescence reaction, and not all diamonds have fluorescence reaction.

Sunlight and fluorescent light contain ultraviolet rays, which makes diamonds with fluorescent reaction look particularly bright and beautiful. Only among diamonds with particularly strong fluorescence reaction, some diamonds will affect their transparency, so diamonds with particularly strong fluorescence reaction are excellent if their transparency is not affected.

Twelve. comment

Remarks column is a supplement to the diamond features not listed in the above columns or unnecessary in the attached drawings, such as:

(1) Veins or grain lines: Veins are usually not considered as included features unless they are colored, reflective or whitish, and are not drawn on the drawings. According to the obvious degree of its appearance, the veins are divided into (1)NIL none; (2) slight; (3) The doctrine of the mean is easy to see; (4)4) Significantly equal to Grade 4, and only obvious veins are recorded in this column. For example, the surface grain is not shown (the surface grain is not shown in the drawings). The internal grain lines are not shown (the internal grain lines are not shown in the drawing).

(2) Not shown in the drawings. For example, minor details of polishing are not shown. Additional pins are not shown (some pins are not shown in the drawings).

(three) the main proportion, angle or symmetry is not good. For example, the arch angle is greater than 35 degrees (the arch height is greater than 35 degrees).