Colour evolution of the oxide layer formed on the Au-25Fe AND Au-24.5Fe-0.5Co




Magnetite, oxide layer, coloured gold alloys, colour theory


The colour theory proposed by Heavens in 1991 has been applied to calculate the thickness of magnetite thin layers, Fe3 O4 , which were obtained by heat treatment at 250 °C in a gold alloy (Au-24.5Fe-0.5Co). The reflectance spectra obtained from the polished samples with different oxidation (and colour) degrees were used to calculate the real part of the refraction index and the (imaginary) extinction coefficients of both the metallic substrate (n2 , k2 ) and the magnetite layer (n1 =2.42, k1 ). The a+bλ+cλ2 form was taken adjusting parameters between experimental and theoretical curves. The fitting of the data resulted in deviations between 2 and 10% for thicknesses in the range of 0 nm (only substrate) and 65 nm (dark blue colour). By means of a mathematic model and following the Heavens’ theory, the thickness of each layer has been predicted with high precision, using the spectral reflectance. Consequently, we propose that by using this methodology, the values of the extinction coefficients of the oxide species can be easily obtained, and the thicknesses of the oxide layers can be predicted. The magnetite thickness values found in this study fall into the interval reported in the literature for first-order interference in steels, from light-yellow (~46 nm) to blue (~72 nm).

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Author Biographies

Sandra Milena Restrepo-Arcila, Universidad de Antioquia

Departamento de Matemáticas, Facultad de Ingeniería, Docente de cátedra

Alejandro Iván Echavarría-Velásquez, Universidad de Antioquia

Profesor Departamento de Ingeniería de Materiales

Facultad de Ingeniería

Marco Antonio Giraldo-Cadavid, Universidad de Antioquia

Profesor Instituto de física, Facultad de Ciencias Exactas y Naturales

Jorge Andrés Calderón-Gutierrez, Universidad de Antioquia

Profesor Departamento de Ingeniería de Materiales, Facultad de Ingeniería

Héctor Darío Sánchez-Londoño, Universidad de Antioquia

Profesor Departamento de Ingeniería de Materiales, Facultad de Ingeniería


T. Burleigh et al., “Anodizing Steel in KOH and NaOH Solutions”, Journal of The Electrochemical Society, vol. 154, no. 10, pp. 579-586, 2007.

Brigham Young University, Silicon Dioxide SiO2 . [Online]. Available: Agosto 2013. Accessed on: Aug. 1, 2013.

Finishing Industry ®, Questions regarding chemical reaction that occurs when Bluing Steel, 2007. [Online]. Available: Accessed on: Feb. 1, 2013.

Ether (Atmospheric Chemistry Data Centre), Real and imaginary indices of refraction of hematite particles at T=293 K. [Online]. Available: Accessed on: Jan. 1, 2013.

F. Constable, “Spectrophotometric Observations on the Growth of Oxide Films on Iron, Nickel, and Copper” Roy. Soc. Proc., A, vol. 117, pp. 376-387, 1928.

Simply Tool Steel, Temperature Color Guide. [Online]. Available: Accessed on: Jul. 1, 2013

L. Muller, “Coloring a gold alloy”, U.S. Patent 5 059 255 A, Oct. 22, 1991.

C. Cretu and E. Van der Lingen, “Coloured gold alloys”, Gold Bulletin, vol. 32, no. 4, pp. 115-126, 1999.

V. Antoniazzi, “Goldlegierung mit irisierender, blaeulicher farbe, verfahren zu ihrer herstellung und ihre verwendung”, DE Patent 3 641 228, Dec. 3, 1986.

American Society for Testing Materials (ASTM International), Standard Test Methods for Determination of Gold in Bullion by Fire Assay Cupellation Analysis, ASTM Standard E1335-08, 2008.

IndiaMART, Induction Casting Machine Bego (fornax) [Online]. Available: Accessed on: Jun. 1, 2013.

O. Heavens, Optical properties of thin solid films, 1st ed., New York, USA: Dover Pub., Inc., 1991.

Y. Fujimura, “Numericalization of the temper color by the oxide film thickness”, Journal of the Japan Society of Precision Engineering, vol. 38, no. 454, pp. 902-907, 1972.




How to Cite

Restrepo-Arcila, S. M., Echavarría-Velásquez, A. I., Giraldo-Cadavid, M. A., Calderón-Gutierrez, J. A., & Sánchez-Londoño, H. D. (2016). Colour evolution of the oxide layer formed on the Au-25Fe AND Au-24.5Fe-0.5Co. Revista Facultad De Ingeniería Universidad De Antioquia, (78), 62–68.