Diamond Changes Color
Year: 2025
Type: article
Abstract: DIAMOND CHANGES COLOR Nona DronovaProfessor of Geological and Mineralogical SciencesORCID: https://orcid.org/0009-0007-4867-9074 Abstract The transformation of rough diamonds into polished stones is a complex technological process that can produce side effects, one of the most significant being a change in the stone’s coloration. This research presents causes, mechanisms, and statistical patterns of such color changes, based on data from the State Depository of Precious Metals and Gems (Gokhran) and the Central Research Institute of Geological Prospecting for Base and Precious Metals (TsNIGRI). Laboratory and electron-microscopic studies demonstrate the role of N3 centers, plastic deformation, slip lines, and impurity redistribution in the development of yellow and brown tints. The findings may help predict the final color grade of polished diamonds. Keywords: diamond color change, N3 center, fluorescence, plastic deformation, yellow tint, cutting defects 1. Introduction The free purchase of diamonds in Russia makes them one of the most convenient investment instruments, concentrating exceptional value in a small unit of weight.The transformation of a rough diamond into a polished stone involves complex technological steps, during which side effects may arise. Among these, the most market-significant is a change in the stone’s coloration. Research by Gokhran and TsNIGRI has improved cutting technology, reducing the occurrence of undesirable coloration, though in certain cases it still occurs. This article examines the causes and patterns of these changes. 2. Factors Influencing Color Change Diamond quality and price depend on both the initial rough and the specific conditions of processing. The crystal structure and optical properties, particularly color, are determined by impurities and color centers (defects). Redistribution and interaction of these centers during processing can cause either subtle or significant changes in color grade. Colorless and faintly tinted diamonds make up a large portion of the rough supply. The optical absorption edge of diamond lies in the ultraviolet; hence, colorless stones exhibit near 100% transmission in the visible range. Even slight coloration reduces this noticeably. 3. Observed Processing Effects In 50% of cases, colorless diamonds (grades 1 and 2) develop yellowish tints — from barely perceptible to distinctly visible — during processing. Only 5% retain their initial grade.Similar effects occur across other color groups, with causes ranging from activation of structural defects to redistribution of impurities. In some cases, more deeply colored stones lighten. 4. Statistical Data Table 1. Color distribution of polished diamonds after processing Rough grade Size I II III IV V VI VII VIII IX 4 gr, 1–2 cl, small <4 14 38 41 38 13 27 8 - - 4 gr, 1–2 cl, large <4 4 8 37 38 6 4 3 - - 5 gr, 1–2 cl, small <4 5 26 36 15 8 3 2 - - 5 gr, 1–2 cl, large <4 3 25 32 12 10 3 - - - 7 gr, 1–2 cl, small <4 4 20 26 14 15 7 8 4 - 7 gr, 1–2 cl, large <4 3 25 24 9 13 6 4 5 - 9 gr, 1–2 cl, small <4 4 26 20 17 15 6 8 4 - 9 gr, 1–2 cl, large <4 4 44 31 29 17 2 3 1 - (Data from Gokhran and TsNIGRI archives) 5. Role of N3 Centers Yellow coloration in diamonds is most often linked to the N3 defect — a group of three nitrogen atoms with a vacancy. Depending on concentration, this defect can produce tints from faint to vivid yellow.In some colorless stones lacking measurable N3 defects, bluish fluorescence may still appear. Bluish fluorescence from N3 centers is typically accompanied by yellow coloration. 6. Fluorescence Changes Table 2. Fluorescence changes in diamonds during processing Group / Size Initial Fluorescence (rel. units) After Processing (rel. units) Colorless (small) 5–27 27–54 Colorless (large) 7–18 35–72 Grade 7 (small) 12–20 20–50 Grade 7 (large) 10–22 32–64 7. Microscopic and Electron-Microscopic Observations Electron microscopy of processed diamonds shows traces of plastic deformation, including slip lines on stressed crystal planes.During cutting and polishing, friction and localized heating produce vacancies and dislocations in the surface layer. Dislocations can: migrate to the surface, be trapped by internal heterogeneities, create localized high-energy zones. Dislocations often attract impurity atoms, forming stable atmospheres. The combination of N3 centers and slip lines frequently results in yellow-brown coloration. 8. Conclusion Processing increases the number of color centers in most diamonds. Even defect-free rough can develop such centers under mechanical and thermal stress.Understanding the interaction of N3 centers, dislocations, and plastic deformation helps predict final color grades, aiding in sorting, valuation, and technological optimization. DOI: to be assigned upon Zenodo uploadORCID Author ID: 0009-0007-4867-9074License: Text – CC BY 4.0; Images – CC BY-SA 4.0Repository: To be archived in Zenodo and Academia.edu for open-access public use.
Author: NONA, Dronova
Language: English
Subfield: Materials Chemistry
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W6931208712
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