The "speed" method mainly takes five aspects of a diamond as parameters, namely, table top (S), bottom tip (P), fisheye (E), waist edge (E) and full depth ratio (D).
1, the square of the table
First, the countertop should look like two crossed squares.
(1) See if the desktop is symmetrical and even.
(2) See if the edge is straight.
(3) Whether the star facet of the mesa is in a regular shape.
(4) whether the mesa is too big or too small
(5) Is the center of the table in the center of the gem?
2. the tip of the steak
(1) Check whether the bottom tooth tip exists and is damaged.
(2) Whether the two edges of the pavilion intersect at a point, and whether the surface edge of the pavilion and the surface edge of the crown are symmetrical.
(3) Is the bottom tip in the center of the gem?
(4) The ratio of bottom to tip is
3. Fisheye lens
Looking down vertically from the front of the gem, if we can see the shape of the waist edge reflected on the diamond, then we say it is a "fisheye diamond". Too shallow a pavilion will produce a "fisheye effect" and too deep a pavilion will produce a "black-hearted diamond". If it is an "eccentric drill", it will produce a crescent-shaped reflection on the edge of the diamond.
Compared with GB, the correct pavilion depth is 465,438+0.5%-45%, and it is limited to 42%-45% in SAN D.N. (1980).
4. Marginal girdle
(1) Is the diamond round or fancy-cut symmetrical?
(2) Whether the waist edge is faceted and polished.
(3) Whether the waist edge is too thin, medium or too thick.
(4) Is the waist edge parallel or inclined to the desktop?
(5) Whether there is a wavy waist edge.
Note: If the waist edge is thin, similar to a knife edge, you need to indicate "Danger" on the evaluation sheet, because the waist edge of the knife edge is easy to break.
5. Depth percentage
According to NCJV, the optimum depth ratio should be 60%~58%. The proportion of 62% is also acceptable, but if it is outside 62% ~ 58%, it is a poor cutting. In China, the total depth ratio of diamonds specified in GB/T- 16554( 1996) can be between 56% and 63.5%, so we should consider our national conditions and make an appropriate evaluation.
NCJV classifies diamonds into four grades: high quality, good, medium and poor. If the aspect ratio of a diamond is 60%, but all other items are poor, then the diamond must also be classified as "poor". If the grade of a diamond is closer to "high quality", then its above five conditions must be closer at the same time. If one item fails to reach "high quality", then its level can only be set to "good". In the appraisal, if the grade is considered to be below "medium", the score will be deducted from 0% to 5%. Similarly, if the grade is higher than "Good", add 10% to 15%.
In the table on the left below, according to the price information of NCJV, we can see that the price increase of NCJV is based on the "medium" grade, and when the quality is "medium", the price increase base is 0%. In the "Guide" of the United States (see the right of the following table), the position with a markup base of 0% is equivalent to the place with a NCJV rating of "good".
NCJV price information
―――― +20%
Very good |
―――― + 15%
Good |
―――― +5%
Medium | 0%NCJV
―――― -5%
Poor |
―――― -25%
American publications
guidebook
―――― + 10%
Very good |
―――― + 5%
Ok | 0% NCJV
―――― -5%
Medium |
―――― - 15%
Poor |
―――― -35%
Price increase standard:
High quality: 15% ~ 20%
With extraordinary fire color and brightness;
Now it is rare in the general market. It has a high color level and looks very different.
Unless all the perfect conditions of "speed" are met, it cannot be easily defined as "high quality".
Good: 5% ~ 15%
The best level that is usually visible;
It has a symmetrical table top-good cutting-almost no fisheye-the table top is not inclined-good waist edge -59% ~ 6 1% full depth ratio.
Medium: positive 5% ~ negative 5%
Reasonable cutting-the relative standard ratio that can be encountered-the table top is a little asymmetrical-the table top or the bottom tip is a little eccentric-you can see a little fisheye effect-the middle/thick waist edge-the overall depth ratio is 57% ~ 63%.
It should be pointed out that the price index of NCJV is based on this level.
Poor: negative 5% ~ 20%
Diamonds with poor quality are basically "dead diamonds" in the market. The fire color is not obvious-the desktop is asymmetrical-the crown is inclined and eccentric-the edges of each face do not intersect at one point-the waist edge is thick or thin with wavy waist edge-the bottom tip is eccentric-and the total depth ratio is less than 55% or more than 65%.
In essence, NCJV's "speed" evaluation method still revolves around the idea of diamond "4C" classification, and combines practical experience to reasonably simplify the complex working elements of diamonds into five simple and easy-to-use steps. It takes a skilled diamond appraiser about 10 ~ 20 seconds to determine the quality of this diamond. I believe that speed will make you a handy diamond appraiser.