The original research process circa 1980 involved locating photographs or line drawings of the stone to be duplicated. This process was slow and tedious, as computers were somewhat of a rarity with limited capability. There was no such thing as the internet or email, and one round-trip of correspondence with an authoritative source could take weeks.
Once suitable documentation was found, tracing paper was placed over the photo or drawing, and the facet pattern of the crown and pavilion would be painstakingly transferred to the paper. Trigonometry would be used to analyze the facet pattern to calculate the angle and index setting for each facet. All this, of course, tempered by seven years of stone-cutter’s judgment. Each step had its inaccuracies, so the final stone was a close approximation of reality. Good enough for display, but more of a representation than a true replica.
Fast forward to today. Computers have more computing power, the internet allows near-simultaneous communications, and graphics programs abound. References are no longer restricted to documents at the local library, but can be purchased from the internet or provided through inter-library loans. Communication and coordination with museum curators, professional cutters, and others are increased by orders of magnitude by email. Progress made in all these factors now allow far more accurate replicas to be created.
One side note. Remember the historical inaccuracies mentioned earlier that are on the web? These are the result of the older technologies that limited communication and coordination, but at the time the researchers did the best they could with what they had. The discoveries made today would not have been possible even five years ago as the technology had not progressed far enough (such as the programs used to model the Hope diamond). The researchers shouldn’t be faulted, but some information does need to be corrected.
The research process in use now starts by locating pictures or drawings of the stone to be duplicated. In all cases, a photograph is preferentially used over a line drawing, as drawings are subject to artist interpretation. A photo captures the stone objectively, it only records what the camera sees. Although photos can be in error to a certain extent due to parallax, spheroidicity of the lens, and other optical errors, they are the most accurate interpretation of reality. Parallax is potentially the most serious error, but professional photographers realize this and it is assumed that this is considered by a professional when provided a once-in-a-lifetime opportunity to photograph one of these phenomenal diamonds.
In some extremely rare cases, the research presented here is performed on the real stone. This was the case deriving the data on the Hope diamond as a result of a Discovery Channel program. This subsequently led to a chance to measure the Blue Heart (Unzue Heart). In the case of the 186 carat version of the Koh-I-Noor diamond, Coster Diamonds in Amsterdam loaned one of their two glass models made circa 1851. One of the two plaster casts made of the stone in 1851 was borrowed from the Natural History Museum in London and studied over a period of four months. These are more preferential than using the numerous line drawings of this stone, as whose version is to be used, Bauer, Dieulafait, or someone else?
Line drawings of the pavilion and crown are drawn only after the best raw data has been obtained and analyzed. This is done by converting a drawing or photo into a digital format, and magnified anywhere from 3-30X. Lines are drawn at the edge of each facet with to-the-pixel accuracy until the full pattern materializes. In many photos, lines can be very indistinct, and in these instances, stonecutter judgment is tempered by knowledge of ancient cutting techniques and cultural preferences to fill in these areas.
Size, shape, and facet pattern must be accurately determined. This is no small feat, even though it could be reasonably be expected that these are all documented for any world famous diamond. Wrong! There is only one place I’ve been able to find that lists the dimensions of the Cullinan III-IX diamonds (excerpts from the Asscher diaries in the back of Balfour’s book). Not even the Royal Collections, Tower of London, or even the Queen of England had them, and they technically belong to her! The Blue Heart, residing in the Smithsonian for almost 50 years, has been weighed, but its dimensions have never been published, and as of this writing (September 2006), are unknown even to the Smithsonian (soon to be corrected).
The line drawings are used to virtually “cut” the stone using a program called GemCad (www.gemcad.com). This program not only allows for determining the cutting angle and setting for each facet, but it also permits the cutter to become familiar with the actual cutting process. Interrelationships between facets, cutting sequence, and similar issues are discovered. This is extremely important, as learning this on a piece of rough is not only time-consuming, but expensive. Although cubic zirconia is relatively cheap, destroying a 2000 carat piece of rough unnecessarily involves a cost in money, time, and wear and tear on equipment that should be avoided.
Cutting a stone on the computer is a highly iterative process that can be very tedious when absolute precision is required. The simplest of diamond cuts, the standard brilliant, has 57 facets placed in a regular pattern, and each has its own angle and index setting. Fifty seven facets with two variable each, and you are simultaneously solving for 104 variables. (This is somewhat of an exaggeration. For symmetrical patterns, the variability is considerably reduced.) Try solving this for an irregular pattern such as the 186 carat version of the Koh-I-Noor, irregularly shaped with 169 facets, and it becomes quite a chore to duplicate. A slight variation on one facet affects all its neighbors, which affects all their neighbors, so a change on one facet affects the entire stone. It is not an easy process to juggle all the variables, which is why this phase can easily take 50-100 hours for a moderate-to-difficult facet pattern. And this is time invested before the rough even touches the machine.
Once the GemCad file is created, it is imported into a document containing the cutting instructions, dimensions, and life-size drawings of the stone from all angles. This document serves as the reference for the cutting process. Cutting is done using a very old Ultra-Tec and standard processes. A 20X optical comparator is used to insure dimensions of individual facets on the stone match those in the line drawings. On facets larger than about 10 mm, a digital caliper accurate to 0.01 mm, and a table gauge accurate to 0.1 mm are used. Digital calipers are readily available from almost any tool department, the table gauge can be ordered from the GIA. It cannot be stressed enough that anyone who wants to create accurate replicas needs to have these three items, or tools with similar capabilities.
As good as GemCad is, and it is outstanding for this purpose, it still has its limitations. It is difficult to transfer the outline of the stone in the diagram to the computer model, especially if the girdle is ground and not faceted. The derived angles and settings still need to be tempered by stone-cutter judgment. There are nuances of the cutting process, such as stone-centering, over- and undercutting, stonecutter technique, and limitations of the faceting equipment, that can alter the calculated values. Many famous diamonds were not cut for symmetry, especially the historic Indian stones, which greatly increases the difficulty of creating an accurate replica using this program.
One last note. As you may have already noticed, the research is exhaustively meticulous. It should go without saying that the data presented here results from the cooperation of many individuals and organizations that share the common goal of accurate scientific knowledge. These people cannot be thanked enough for their support, and hopefully all their efforts have been duly acknowledged.