Eﬀects of cobalt, copper, manganese and titanium oxide additions on the microstructures of zinc containing soft porcelain glazes Bekir Karasu*, Servet Turan University of Anadolu, Department of Ceramic Engineering, I . ki Eylu ¨l Campus, Eskis ¸ehir, Turkey Received 31 May 2001; received in revised form 27 August 2001; accepted 19 September 2001 Abstract Diﬀerent types of glazes, which are nearly all based upon silicate compositions, are used to meet a wide range of requirements in service. Many artistic eﬀects are achieved by departing from a clear, smooth, transparent system. Coloured glazes are produced by several means such as the inclusion of colouring oxides, addition of stains, dispersing ﬁnely divided particles and the use of precious metals, applied in the form of lines or bands, or even screen-printed patterns. Colouring oxides commonly used include iron, cop- per, cobalt, chromium, manganese, nickel, vanadium, cadmium and selenium. Zinc oxide has a beneﬁcial eﬀect in many coloured glazes amongst which crystalline ones are more noteworthy. With this paper the eﬀects of CoO, CuO, MnO 2 and TiO 2 additions into zinc oxide containing crystal glazes diﬀerentially heat-treated are described on micro-scale appearances. Experimental techni- ques used were X-ray diﬀraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDX). # 2002 Elsevier Science Ltd. All rights reserved. Keywords: Additives; CoO; CuO; Glazes; Microstructure; MnO 2 ; TiO 2 1. Introduction Most of important elements used as a source of colour in glazes and enamel stains are to be found in a particular section of the Periodic Table known as the transition elements. They can readily form complexes in solution. This means that they can associate with two or more surrounding ions of opposite sign, sometimes known as ligands, to form a complex group, the properties of which may be very diﬀerent from those of the original ion. The surrounding ﬁeld can change the characteristic energy levels in such a way as to bring about a complete change of colour. There are a number of colouring media used in ceramics and they may diﬀer from each other in fundamental ways. 1 The absorption of char- acteristic wavelengths by elements dissolved in the glaze or by inert pigment particles suspended in the glaze produces colour. Some elements, such as Pb and Zn, do not themselves contribute any colour, but have a considerable inﬂuence on the colour produced by other ions. Zinc oxide is a valuable auxiliary ﬂux in glazes ﬁring up to about 1050  C. At higher temperatures, it is eﬀective in viscosity reduction and the amount added to a glaze recipe should be adjusted to needs. By its use the ﬁring range of high temperature glazes is extended. While some glazes mature, zinc oxide will dissolve readily even if present in excessive amounts. On cooling, crystals appear as those formed from a saturated solution. The ﬁne crystals collect any pigment or colouring ion present in the glaze to give highly decorative eﬀects. 2 Although cobalt was isolated only in the eighteenth century, its use as a glass colorant has been known for about 4500 years. Nearly all glasses develop a blue colour with cobalt (as Co 2+ ), although in some compositions a pink one will develop. The solubility of cobalt salts in glass is high. Cobalt is a powerful colorant and as little as 0.02% CoO produces a noticeable tint in a transparent glaze. 2 As one of the strongest colouring elements, copper was one of the earliest colorants of glaze in early Egyptian faience. It gives a wide range of colours from blue to green and in special circumstances red depending upon composi- tion and the ﬁring atmosphere. Copper compounds are 0955-2219/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved. PII: S0955-2219(01)00456-3 Journal of the European Ceramic Society 22 (2002) 1447–1455 www.elsevier.com/locate/jeurceramsoc * Corresponding author. Tel.: +90-222-3213550x6357; fax: +90- 222-3239501. E-mail address: bkarasu@anadolu.edu.tr (B. Karasu).