INDUSTRIAL APPLICATIONS Anodic Coloring of Titanium and Its Alloy for Jewels Production M. V. Diamanti,* B. Del Curto, V. Masconale, C. Passaro, M. P. Pedeferri Department of Chemistry, Materials and Chemical Engineering, Politecnico di Milano, ‘‘G. Natta’’—Via Mancinelli 7, 20131 Milan, Italy Received 9 July 2010; revised 9 November 2010; accepted 8 December 2010 Abstract: Anodized titanium with its interference colors, its appearances and its light, is undoubtedly of great appeal to the field of architecture and to all ramifications of design, to visual communication and to the world of fashion. On its surface, it is possible to create a visionary world of colors, perfectly controlled by the imposition of determined anodizing parameters and surface conditions. This article presents one of the applications of anodized ti- tanium, which most earns general interest nowadays in the designers’ world, that is, the production of colored tita- nium jewels. Since titanium is considered a seminoble metal, its use is mainly directed to small series production: therefore, a good know-how giving high reliability of the anodic coloring process is required. The chosen procedure will be described, together with a full characterization of the obtained interference colors. Ó 2011 Wiley Periodicals, Inc. Col Res Appl, 00, 000 – 000, 2011; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/col.20683 Key words: color appearance; anodizing; design; inter- ference color; titanium INTRODUCTION Traditionally, jewels were identified as precious, unique objects composed by a combination of noble metals (silver, gold, and platinum) and stones (diamonds, emer- alds, and sapphires), produced and decorated by the hand- craft manufacturing of expert goldsmiths. 1–3 However, recently, the concept of jewel has experienced a change because of market segmentation, which now gives a diversified offer: from high-target noble jewels to low-tar- get ones, in which non-noble and seminoble metals have gained importance. As a consequence, large improvements have been made in those fields of jeweler’s craft that use steel, aluminum, and titanium. Processing methods often diverge from the traditional techniques used in jeweler’s art, to adjust to the logics of series production. The most commonly applied technique consists of a first plastic deformation step followed by either mechanical or galvanic surface finishing (most likely, electropolishing or anodic oxida- tion): non-noble metals surface treatments represent one of the most interesting fields for the application of surface science in this world, as demonstrated by the countless spinoffs in technologically advanced fields. 4–6 As for titanium, anodic oxidation can be used to confer to the surface a colored appearance thanks to the forma- tion of an oxide layer, 5 to 100 nm thick: interference taking place between the oxide and light results in the appearance of colors on the metal surface, whose hue is determined by the optical thickness of the oxide itself. 7–12 *Correspondence to: Maria Vittoria Diamanti (e-mail: mariavittoria. diamanti@polimi.it). Contract grant sponsor: Italian Ministry of University and Research (MIUR). V V C 2011 Wiley Periodicals, Inc. Volume 00, Number 0, Month 2011 1