Diamond is perhaps one of the most valuable natural stones. The properties of the diamond used in industry and jewelry carry it to the top. Diamonds are extracted from the deep layers of the earth. So how are diamonds processed? We know that the diamond was created by cutting. So, a diamond is cut, does it always have to stay the same? No. Diamonds can be cut by jewelers again and again. We call these phenomena recutting.
Diamonds can be cut by jewelers in the scope of recutting. The main purpose of recutting is to redefine the proportions of a diamond to enhance its beauty. There are some examples of diamonds whose clarity has been increased by re-cutting. Sometimes, by re-cutting, both the proportions and clarity of the diamond can be improved. This increases the value of the diamond. The ability to calculate the weight of a diamond after it has been re-cut is very useful to anyone interested in diamonds. However, some precautions must be taken when calculating the weight of the recut diamond. A wide variety of factors must be taken into account in order to do it properly.
Re-Cutting Old-Fashioned Diamonds
Two common old cut styles are the old metal cut and the old European cut. These diamonds can be recut into modern diamonds with some weight loss. In general, they have heavy crowns and cones, but a few may have flat cones. Sometimes it’s not worth the effort as re-cutting these flat-cone diamonds results in too much weight loss. There are two different types of old-mine segments that are commonly seen:
a) Those with a square-like beltline and b) Those with a rectangular beltline. The problem with recutting old-mine cut diamonds is finding the right balance between weight loss, clarity, shape, and proportions. In other words, the question is: what will be the value of the diamond once it is cut again, and will it be easily sold? In a rectangular-shaped diamond, the best recut would be an emerald or oval cut. Because in these cut shapes, more weight is preserved than the round diamond cut.
Diamonds with a square-like beltline are recut into round diamonds. These diamonds are rounded to remove excess corners. And again, the cut diameter is the narrowest that the original square diamonds have. Another solution is to cut a square-shaped diamond into a square emerald. However, such diamonds are rare, as they are not very popular and do not sell well.
Old European style cuts can easily be cut into modern diamonds. Because the diameter of the diamond remains the same. Old European cut diamonds usually have small tables, heavy crowns, and floors ranging from 40% to 48%. Re-cutting widens the table and reduces the height of the diamond. The average height should be reduced to approximately 59%. The weight loss will be less because the height has not been reduced much and the diameter has remained the same.
Repairing Damaged Cut Diamonds
Re-cutting damaged diamonds can result in a minor or major weight loss. One or two points (.01-.02 carats) of weight can be lost when a small crack or scratch is cut. However, often minor repairs result in less than 1/2 point (.005) weight loss. On the other hand, sometimes a piece of a diamond can split and break. This often happens close to the belt area. If the slit has gone too far into the stone, the solution may be to re-cut the diamond into a fancy half-moon shape. Another solution is to repair the diamond, which requires the use of a proportion scope.
The first step in calculating the recut weight of such diamonds is to measure their smallest diameter (percent of a millimeter) and height. To repair such a diamond, it is necessary to slightly reduce its diameter. To calculate this reduction ratio, place the diamond table side down on the glass disc of the proportion scope. Then adjust the diamond and screen until you measure correctly. The second step is to apply the formula: Smallest diameter x (100% – the percentage of belt diameter destroyed) = estimated new diameter of the diamond.
Next, divide the diamond’s estimated new diameter by its height to find the new percentage of average depth. In this case, there are two possibilities:
If the new average depth percentage of the diamond is equal to or less than 59%, apply the formula: New estimated diameter of the diamond x current height x .0061 = Estimated recut weight
If the percentage of new average depth is greater than 59%, multiply the new diameter of the diamond by 59%. This result will be equal to the new millimeter height of the diamond. New diameter of the diamond x new height of the diamond x .0061 = estimated recut weight
It should be noted that this method cannot be applied to heavily damaged diamonds. Generally, both height and diameter must be reduced in cases where diamonds are heavily damaged. Therefore, it is best to use the high crown, flat cone cutting method when calculating the recut weight of heavily damaged diamonds.
Re-Cutting a Flat-Crowned Flat-Cone Diamond
In this case, the cutter will reduce the diameter of the diamond and maintain the same height. In this case, the goal is to keep the maximum weight by reducing the diameter as little as possible while trying to enhance the beauty of the diamond. We mentioned earlier that the best possible cone angle is 40 3/4 o. It results in a 43.1% cone height percentage. The most logical choice for the cone height would then be 43%.
A 2% belt should be thick enough to mount and securely attach to a set. The percentage of crown height is chosen according to the weight conservation purpose. The wider the table, the thinner the crown, but also the more weight. The smaller the table, the higher the crown and more weight loss. Try to find the right balance between the two to find what suits your personal taste in terms of brightness and light emissivity.
Table % – Crown height %
54% – 15.7%
56% – 15.2%
58% – 14.5%
60% – 13.8%
62% – 13.0%
64% – 12.3%
66% – 11.6%
68% – 11.0%
When calculating the re-cut weight of a flat-crowned flat-cone diamond, the following procedure should be followed:
- Select the table percentage.
- Determine the appropriate crown height.
- Calculate the estimated percentage of new depth. To do this, take the cone height, the belt thickness, the crown height and add up these three.
- Divide the current millimeter height by the new percent depth to calculate the new diameter.
- Then apply this formula: New diameter x current height, x .0061 = estimated recut weight.
Note the weight difference between these two re-cut methods. By changing the table size, you have gained a certain carat weight. This ratio makes a big difference in the value of the diamond. So, in this case, the closer you get to the American ideal cutting ratios, the more weight you will lose. Therefore, European cutting is recommended for recutting this diamond.
As you can see, there are different ways to maintain weight. A bit more weight can be gained if the cone is recut close to 41%, but it should be noted that diamonds are recut to increase their beauty. Therefore, a 43% cone will be the best choice. A similar result can be achieved by cutting a thinner belt, but due to durability problems, this is not recommended. For all these reasons, when you have to re-cut a very flat diamond, choose a cone height very close to 43%, an arch thickness of 2%, a crown angle between 32 and 34 ¼. The only exceptions to these standards may be:
To achieve a very desirable weight such as 1/2, 1, etc. carat.
The possibility of increasing the clarity ratio by removing a small speck that is too close to the surface of the diamond.
In all other cases, try to meet the standards given above. In conclusion, here is a summary of the procedure to be applied to calculate the recut weight of a flat crown, flat cone diamond:
- Select the cone height percentage (usually 43%, never less than 41%)
- Take 2% belt thickness to avoid durability issues.
- Choose crown height percentage (an angle between 32 o and 34 ½ o)
- Add the selected crown height, arch thickness, and crown height percentage selected to find the average percentage depth selected.
- To calculate the estimated recut weight, measure the diamond’s millimeter height and divide this height by the percentage of average height selected.
- Now apply the formula: Estimated recut diameter x actual height x .0061 = estimated recut weight
Recutting Other Types of Diamonds
- Re-cutting a rough” or very deep diamond
A “rough” diamond is simply a problem of re-cutting. This style of cut is seen in old-fashioned diamonds with an old metal cut (having a square-like belt line) and an old European cut (with a rounded beltline). When these diamonds are recut into modern diamonds, the cutter will reduce the diamond’s average height without reducing the diameter for the old European cut, and round the belt to the smallest diameter for the old metal cut.
Crown and cone angles will be corrected and the table portion will be enlarged. After cutting again, the diamond appears to have the same size as before, because the belt diameter is approximately the same, but the beauty of the diamond has increased immensely. To calculate the estimated recut weight, simply multiply the estimated new millimeter height by 59%. This result would be approximately the average depth percentage of a medium arched European cut diamond. The following formula applies: Smallest radius x estimated new height x .0061= Estimated recut weight
- Re-cutting a high-crowned flat-cone diamond
A high crowned “fisheye” diamond is seen almost exclusively in older cut styles. When the cutter wants to cut this stone, he has to reduce both the diameter and the height of the diamond. To calculate the recut dimensions of the high crown “fisheye” diamond, it is absolutely necessary to use a proportion scope. The first step in a proportional meter is to find the smallest diameter.
Rotate the diamond to find it. Then enlarge the image of the diamond so that the American ideal line fits perfectly inside the magnified diamond on the screen. Check that the image of the diamond is not enlarged any more than necessary. After that, move the screen until you read the same number on both sides of the ruler. Note that each unit on the ruler is equal to 2%. Make the calculation according to %1. Next, divide the smallest diameter of the diamond by the excess units to find the new diameter of the diamond, and multiply the new diameter by 59% to find the new height of the diamond. In this case, apply the formula: Estimated new diameter x estimated new height x .0061 = estimated recut weight.
- Re-cutting a flat-crowned, deep-cone diamond
This type of diamond is usually seen in modern cuts but is sometimes found in old-style cuts as well. Deep cones are very easy to spot diamonds because when viewed from above these diamonds appear black in the center. Re-cutting such diamonds does not result in huge weight loss. It is usually sufficient to decrease the cone angle to increase the beauty of the diamond. However, in some cases, both diameter and height must be reduced because the crown does not meet the required standards.
To calculate the recut dimensions of a flat crowned deep cone diamond, use the proportion scope and follow the same procedure as for high crown flat cone diamonds. If you are only going to re-cut the cone of the diamond, the existing crown and belt diameters can be preserved. The first step is to calculate the current cone height percentage. The difference in the percentage of cone height can be calculated by subtracting the current percentage of cone height from 43%.
Once this is done, calculate the current average percentage depth of the diamond and subtract the difference in the percentage of cone height from the percentage of current depth to find the estimated percentage of new depth. Then, to calculate the estimated new millimeter height, multiply the estimated percent new depth by the average diameter, and apply the formula: Average diameter x estimated new height x .0061 = estimated recut weight
Recutting Examples
Example 1:
- Given: A round brilliant diamond
- Weight: 1.15ct
- Clarity: VS1 (A small fluff on the cone surface)
- Finish: Medium (18%) due to high crown
The finish grade of this diamond can be reduced to a “fine” category by reducing its weight by 0.03 ct. The degree of clarity is also improved by re-cutting the cone surface. This will result in a weight loss of 0.04 carats and the clarity grade will increase to the IF category. There will be a weight loss of 0.07 ct with this re-cutting process. So your diamond is 1.08ct, has a clarity grade IF and a finish grade is now “good”. The difference in value between before and after cutting again makes the transaction profitable.
This example is very attractive, but recutting does not always yield such net profits. It is important to remember that recutting a diamond can sometimes end in disaster. Attempting to remove a large rift can cause it to become larger. Re-cutting a diamond to correct its proportions can cause blemishes to reappear or become visible again. Therefore, careful analysis should be made regarding the nature and location of the spots. Re-cutting generally does not affect the color grade of a diamond. Just removing an area where the color is concentrated, or polishing or surfacing an icy belt can cause a difference in the degree of color.
Oftentimes, jewelers and diamond dealers come to customers asking them to revalue an old cut diamond or ask how much it costs to recut a damaged diamond. A jeweler who can calculate the value of a diamond when it is cut again will have a better job than a jeweler who has no idea about it. As mentioned above, certain characteristics and imperfections of the diamond should be considered when deciding whether to recut an old cut diamond or repair a damaged diamond.
Example 2:
Diameter : 8.60 x 8.66 mm
Height : 4.55mm
Weight: 2.03 carats
Average depth: 52.7%
Re-cut depth percentage when a table is selected at 54%
= 15.7% + 2% + 43.1% = 60.8%.
New diameter = 7.4835 Rounded to 7.48mm.
Now apply the formula:
New diameter x current height x .0061 = Estimated weight or
7.48 x 7.48 x 4.55 x .0061 = 1.5529 1.55 carats are rounded up.
Now, choose a 66% table:
Percentage of new depth = 11.6% + 2% + 43.1% = 56.7%
New diameter = 8.0246 Rounded to 8.02mm.
Estimated recut weight = 8.02 x 4.55 x .0061 =
8.02 x 8.02 x 4.55 x .0061 = 1.7852 rounded to 1.79 carats.
Example 3:
Smallest diameter available = 6.84 mm
Available height = 5.05 mm
New estimated height = 6.84 x 59% = 6.84 x 0.59 = 4.0356 rounded to 4.04 mm.
Estimated re-cut weight = 6.84 x 6.84 x 4.04 x .0061 = 1.529 rounded to 1.15 carats.
Using the same example, you decide to cut the diamond again according to the American ideal cut instead of the European cut. The American ideal cut average depth percentage is approximately 62%. Therefore, multiply the smallest belt diameter by 62% to find the estimated new millimeter height. Then apply this formula: Smallest radius x estimated new height x .0061= Estimated recut weight
A different approach:
Smallest diameter = 6.84 mm
Height = 5.05mm
New estimated height = 6.84 x 62% = 6.84 x .62 = 4.2408 rounded up to 4.24 mm.
Estimated recut weight = 6.84 x 6.84 x 4.24 x .0061 = 1.2100 rounded to 1.21 carats.
As you can see, two different cuts result in two different weights. Therefore, when the diamond to be cut is a “rough” diamond, it is more advantageous to re-cut it in accordance with the American ideal cut. Because it results in the least weight loss.
Example 4:
Smallest diameter available = 7.43 mm
Available height = 4.46 mm
Extreme unit of measure = 109%
Estimated new diameter = 6.6880 Rounded to 6.69 mm
New height = 6.69 x 59% = 6.69 x .59 = 3.9371 rounded up to 3.95 mm.
Estimated re-cut weight = 6.69 x 6.69 x 3.95 x .0061 = 1.0783 rounded up to 1.08 carats.
This method involves re-cutting the diamond according to the European cutting style. However, you can also choose to cut this diamond according to the American ideal cutting style. Therefore, instead of multiplying the diamond’s new diameter by 59%, you can also multiply it by 62% to calculate the new height of the diamond.
A different approach:
Smallest diameter = 7.43mm
Height = 4.46mm
Extreme ruler unit of measure = 109%
Estimated new diameter = 6.6880 Rounded to 6.69 mm
New height = 6.69 x 62% = 6.69 x .62 = 4.1478 rounded up to 4.15 mm.
Estimated recut weight = 6.69 x 6.69 x 4.15 x .0061 = 1.1330 rounded up to 1.13 carats.
As can be seen, two different cutting styles give two different weight results. Therefore, in this case, it is more advantageous to re-cut the diamond according to the American ideal cutting style. Because this standard causes the least weight loss.
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