Wang, H. A. O. (Corresponding author) ; Wälle, M. ; Hutanu, V.MLZ* ; Li, X.MLZ* ; Krzemnicki, M. S.

2025

Abstract: Corundum, encompassing the highly prized ruby and sapphire varieties, stands as acornerstone of the global gemstone market. The allure and value of these gems have historicallydriven the development of various treatment techniques aimed at enhancing their colour andclarity. While many treatments are stable and widely accepted when properly disclosed, theemergence of new or less understood methods presents an ongoing challenge for thegemological community. Accurate detection and disclosure of all treatments are paramount formaintaining market confidence and ensuring fair trade. Gamma irradiation has been exploredas a potential method to alter the colour of various gemstones, including corundum (Ashbuugh,1988; Pardieu et al., 2022). However, the effects of such irradiation on corundum, the stabilityof any induced colour changes, and robust methods for their detection remain areas requiringcomprehensive investigation. This contribution builds upon our preliminary work, presented atthe IGC Tokyo 2023 (Wang et al., 2023), to provide a more in-depth understanding of gammairradiation effects on a diverse suite of corundum samples and to outline a potential detectionmethod.Materials and methods• Sample selection: For this study, we carefully selected 29 natural and synthetic corundumsamples. This selection was designed to represent a variety of colours, including colourless,pink to purple fancy sapphires, rubies and sapphires. The rationale was to assess howdiffering trace element compositions, which are fundamental to corundum's colour,influence the response to gamma irradiation. Four selected samples representing differentinitial colours and elemental concentrations (Mg, Ti, V, Cr, Fe) are presented in Table 1.Elemental concentrations were determined by LA-ICP-TOF-MS.Table 1. Information and initial colours of the selected four corundums as well as their traceelement composition. All numbers are in unit of ppm. “-” indicates that the concentrations arebelow detection limit ~1ppm.Init. Colour Mg Ti V Cr FeSample 1 Nat. Crd. blue 100 175 11 10 2800Sample 2 Nat. Crd. purple 25 50 10 400 540Sample 3 Syn. Crd. purple - 60 0.6 360 95Sample 4 Syn. Crd. purplish red - 5 1 1700 -• Gamma irradiation: The samples were subjected to gamma irradiation at FRM II Facilityfor a continuous period of 70 hours, achieving a total dose of approximately 33 kGy (Li, etal. 2022). This represents a substantially higher dose than in our preliminary investigations,intended to maximize any potential colour alterations.• Post-irradiation handling: Immediately following irradiation, samples were carefullytransferred into an aluminum container. This precaution was taken to shield them fromambient light exposure, thereby preserving any unstable colour centers that might have been(PDF) Effects of Gamma Irradiation on Corundum: Towards a Potential Detection Method. Available from: https://www.researchgate.net/publication/397056082_Effects_of_Gamma_Irradiation_on_Corundum_Towards_a_Potential_Detection_Method [accessed Feb 25 2026].

Keyword(s): Earth, Environment and Cultural Heritage (1st) ; Geosciences (2nd)

1. IRRAD (IRRAD)

1. Irradiation facility