International Diamond Council (HRD, Belgium) as example

Evaluated diamonds are registered and weighed accurate to 0.0001 or 0.0005 ct. A client receives the document confirming the diamond weight and other characteristics, which are kept in a computer file of the laboratory. The diamond is denoted by a number, which serves as an identification in the end of the certification procedure, when the owner receives the certification bill.
Laboratorial processing
The diamond is washed with alcohol and cleaned with pumice powder. Before examination, the stone is washed in sulfuric acid. To make sure that the diamond is genuine, ordinary identification is performed, for example, by measuring its heat conductivity.
Fluorescence of diamond is studied in a specially designed apparatus with a long-wave ultraviolet source and is compared to the fluorescence of masterstones.
Color grading
By color, diamonds can be referred to as Cape series (yellow tint) or as fancy-color diamonds. Cape diamonds are visually compared to the colored masterstones under standard light. To determine the color grade, the absolute identity of color between the diamond and a masterstone should be established at least by four independent experts. The fancy-color diamonds are evaluated by visual comparison of the diamond color to color tables. Stones are also studied by spectrophotometry and spectrofluorimetry analyses for the confirmation of the natural origin of the color. After the thorough examination, the laboratory issues the Colored Diamond Report, a special certificate for fancy-color diamonds.
Clarity grading
A diamond is examined under the HRD microscope, which combines the special lighting system and special stone-holding mechanism. The size of internal features is measured by using the net on the oculars. The clarity grading takes into account the number, size, brightness, and location of the inclusions as well as the number of facets through which these inclusion can be seen. The clarity grade is determined from the table, which considers all these factors, transparency, graining, and external defects. Then the diamond is examined with a 10x triplet loupe to check the correspondence of the inferred clarity grade to the international standards. The clarity of diamond is evaluated independently by three experts.
Cut grading
involves proportion and finish evaluation. Any symmetry features affecting the stone appearance are taken into account. The tools used in cut grading include proportioscope, micrometer, and HRD microscope. Proportion evaluation is conducted only for round diamonds. The proportions of other shapes are measured but not graded, since there are no commonly accepted standards for fancy cuts. The last step of cut grading involves the examination of a stone with a 10x triplet loupe.

The certificate is prepared on the basis of the results of laboratorial investigations, analyses, and computer data bases. The diamond is returned to the client in the original package or in a special plastic envelope sealed together with the certificate microfilm. A special seal guarantees the correspondence of the certificate to the stone.