As an independent consultant, I work with various diamond cutters, dealers, jewelers, auction houses and appraisers, analyzing their coloured diamonds and preparing detailed letters. People refer to these documents as a "Hofer Certificate" or a "Hofer Report", whereas I refer to these documents as a.
Each Hofer Letter is specific to the diamond being examined, presenting a varied blend of facts, measurements, and observations for a particular stone. The letters vary in length, from 5 or 6 pages, up to 30 or 40 pages, depending on the rarity, complexity, or unique history of the coloured diamond. For example, a Fancy yellow diamond that weighs one-half carat may require seven or eight pages to adequately describe the elements of colour (i.e., hue, lightness and saturation), the rarity, and additional information about the cause of yellow colour, where it was found, how it was cut, etc. Whereas, a large and/or famous coloured diamond, like the Agra pink diamond, required over 50 pages to describe the provenance and physical characteristics of this Fancy Intense pink diamond in sufficient detail. This letter was eventually made into a hardcover book.
The Hofer Letters are important documents that travel with the diamond. They provide a thorough explanation of the colour presented in a simple format that enables any collector, investor or dealer to locate the information that interests them most. The Letters provide the basic data necessary to identify the diamond, including the weight, measurements, shape and style of cut. They also provide additional detailed information about the three basic elements of colour: hue, lightness, and saturation. Plus, many other topics such as: beauty, rarity, history, common colour names; how the shape outline, proportions, and facet pattern affect the perceived face-up colour, and in some instances a brief discussion of the colour origin.
Each Hofer Letter is intended to accompany an existing laboratory report from one of the major diamond grading labs around the world. These grading reports are important documents that verify the authenticity of the colour (natural or treated), and various physical characteristics such as weight, shape, measurement, etc. In addition, the lab reports may assign a grade for the clarity, colour, or cut of a particular diamond. In many cases, the colour grade listed on the laboratory report and the colour description listed in the Hofer Letter are in agreement. However, in a number of cases the lab issued colour grade does not match the colour description in the Hofer Letter, indicating disagreement. This disagreement regarding colour description (i.e., colour grading) is quite normal, and directly relates to the methods used by the various diamond grading labs versus the Hofer approach (i.e., subjective colour grading vs. objective colour measurement).
In addition to the Hofer Letters, I also prepare two or three page letters for retail jewelers or private clients. These shorter letters are usually structured in the form of questions and answers about the specific coloured diamond. The questions are selected to address the special features of each individual stone. These so-called "Q & A Letters” provide a convenient checklist for the coloured diamond enthusiast or salesperson to assess the quality and beauty of a particular coloured diamond with ease. Jewelers often utilize these documents when they present a stone to their private clients. Private clients utilize them as a synopsis of pertinent facts about a particular stone.