Diamond Expertise and certification
Like any other product, diamonds are assessed for overall quality and particular characteristics. Unlike many other objects, diamonds are a special commodity: before purchasing one, th e buyer must be 100% certain that the diamond is natural and genuine.
This makes diamond expertise – the procedure of establishing the authenticity of diamonds - one of the most important prerequisites for the purchase.
Diamond certificates issued by independent gemological labs are essentially diamond expertise reports. Although in reality these documents may go by many names - expert opinion, quality report, lab report, quality confirmation document, dossier, or passport – the most common industry term is "certificate". This is the term familiar to most consumers, and it also makes the most sense because, largely, these reports contain information about the diamond's authenticity and quality. A third-party gemological lab report that certifies the authenticity and quality of a diamond significantly affects consumer confidence and the diamond's final price.
Most gemological centers are located in the countries with substantial diamond production. The largest ones have branches all over the world, and their reports are considered the most accurate. However, since diamond expertise standards and methods vary, sometimes the same diamond can get different grading results in different laboratories.
The most well-known diamond grading labs in the world are:
- GIA – Gemological Institute of America;
- AGS – American Gem Society;
- EGL – European Gemological Laboratory;
- HRD – Diamond High Council (Belgium);
- IGI – International Gemological Institute.
In jewelry retail, the availability of a diamond expertise certificate is considered a competitive advantage for a diamond. The certificate is a special document that confirms the diamond's authenticity and lists its weight, color, clarity, type and quality of the cut, and any distinctive features identified in the process of special gemological testing. The certificate ensures that the buyer is purchasing a genuine article with particular characteristics that affect the diamond's value and final price.
The data contained in the diamond expertise report helps identify the stone and so brings added value to the owner in case of loss or theft or when the jewelry piece is given to a workshop for repairs or redesign. Other situations when this information can be useful include subsequent sales, transfer for storage, evaluation, insurance, and other operations. Note that the certification report does not specify the diamond's monetary value.
Decades ago major diamond market players realized the need to regulate the work of various evaluators in order to create common methods and standards of diamond certification. At the 1975 Amsterdam Congress, the World Federation of Diamond Bourses (WFDB) and the International Diamond Manufacturers Association (IDMA) set forth a number of recommendations for diamond expertise laboratories. These included legal and financial independence from diamond-producing and trading entities as well as government agencies, scientific approach, adoption of a well-known evaluation system, and recognition in the laboratory's country of origin.
Each laboratory has its own policy of conducting diamond expertise for synthetic, enhanced, and composite diamonds. When a stone is identified as either of the three, the laboratory may return it to the owner without certification or prepare a report that contains a complete set of information on the diamond's nature. In 2004, WFDB requested all laboratories when dealing with synthetic diamonds and diamonds enhanced using the HTHP (high temperature high pressure) method to issue reports of different colors that would feature the diamond's origin and treatment information in a prominent spot.
During the diamond expertise certification process, each diamond is assigned an ID number, while the identity of the owner, who subsequently picks up the bill, is kept anonymous.
The authenticity of a diamond is established by measuring its thermal conductivity and examining it under a microscope to rule out artificial stones and moissanites. In case of a doubtful origin or color, the stone is then subjected to a spectrophotometric and spectrofluorometric analysis.
The diamond expertise report includes information on the stone's clarity, the symmetry and quality of the final polishing, as well as special charts called clarity diagrams, which differ for each particular type of cut. Usually several experts work with the diamond independently, and the results of each examination are then compared against one another to arrive at the final conclusion.
Grading the diamond's cut includes the assessment of the stone's final polishing and proportions.At this stage, the diamond is inspected for any symmetry flaws that may affect its appearance, using a proportion scope, a micrometer, and a microscope. Proportions are graded for round diamonds but only measured without grading for other shapes, since no universal diamond expertise standards exist for grading complex fantasy cuts.
In terms of color, the two major categories of diamonds are called the Cape series, characterized by a yellowish hue, and the fantasy-colored stones. TheCape series diamonds are compared against the laboratory set of model stones under standard lighting conditions. The color parameters of a diamond are determined by two experts, who compare the diamond's hue to the models independently from one another. The results of their examination are then passed to a third expert who prepares the final conclusion. In case of the fantasy-colored stones, the color assessment part of the diamond expertise is conducted visually and involves comparison against special color tables.
Fluorescence of a diamond, also known as its luminescence, is examined using a device with long-wave ultraviolet light source and then compared with the fluorescence of model diamonds.
The diamond expertise procedure for establishing its clarity involves a 10x magnifying glass and a microscope. Often, a grid on the microscope eyepiece is used to determine the dimensions of the diamond's internal imperfections called inclusions. The number, size, brightness, and position of the inclusions, as well as the number of facets through which they are visible, are taken into consideration. Based on these and other parameters - the degree of transparency, the presence of structural defects and surface blemishes - the diamond is assigned a grade in the clarity chart. Then it is examined through a triplet 10x magnifying lens to verify that its appearance complies with the international standards of the given clarity grade. Clarity must be graded by at least two evaluators working independently.
Upon completion of all these procedures a diamond expertise report is drawn up, containing the following information: the diamond's size, weight, proportions, quality of polishing, cut, color and clarity characteristics, and the diagram for the particular type of cut as an illustration of the diamond's clarity.