The mechanisms of color formation in porcelain containing neodymium oxide, which can change the color by means of the absorption or reflection spectra, depending on the light source, are studied. The optimal content of neodymium oxide in porcelain is determined in the 1976 CIE system, the optimal neodymium oxide content in porcelain is determined, and the dependence of the color of articles on the firing medium and light source is determined.Among the many groups of porcelain articles, hard porcelain with different variants of decoration is now widely used. Artists and designers who use hard porcelain need subglaze paints and pigments, which are also used for coloring ceramics. The number of articles (mainly articles manufactured abroad) with a colored ceramic mass -both single-color and with color variations (the interior of an article is one color and the exterior is a different color) -is continually increasing. Such porcelain is characteristic for china and large decorative interior articles (vases, pots for plants, plaques, panels, and so forth).Oxides and pigments are used in subglaze decoration of porcelain. A few oxides are heat resistant in the firing temperature range of porcelain articles 1350 -1410°C and in a reducing gaseous medium so that the subglaze color palette for hard porcelain is sparse. It is well known that chromium, manganese, and cobalt oxides withstand such firing conditions.Pigments containing iron, titanium, copper, nickel, and other oxides as colorants are also used for subglaze painting on porcelain. High-temperature coloring compounds must be used for subglaze paints for solid porcelain. Such compounds are rare-earth element oxides (REEO). REEO can be used as components of paints for decorating porcelain articles and as a constituent of paste that can color porcelain. A pigment that can be used to color hard porcelain must meet two main requirements: it must be stable in the temperature interval 1300 -1410°C and it must not change color in the range of the oxidation-reduction potential (ORP) of the gas medium used for firing porcelain.It is known that ceramic pigments of the Nd 2 O 3 -Al 2 O 3 system are used as subglaze paints for porcelain and glazed pottery as well as in majolica. Such paints are heat resistant, withstand well firing temperatures in the range 1140 -1350°C, do not give pinholes, dry areas, clumping, and other defects on glaze, and produce very pure and soft rose-lilac tones.The process of synthesizing ceramic pigments with equimolecular ratios of the oxides (Nd 2 O 3 : P 2 O 5 , Nd 2 O 3 : ZrO 2 , Nd 2 O 3 : TiO 2 ) has attracted interest in recent years. For such oxide ratios it is possible to obtain pigments with different palettes suitable for coloring glazes [1].The known temperature dependence of the standard value of the Gibbs formation energy of certain oxides possessing a coloring effect [2] makes it possible to evaluate the reduction of metal oxides in a gas medium with a high CO content (2 -5% 2 ). It is evident that REEO cannot be reduced by carbon mono...

A variant of use of rare-earth metal oxides for decoration of porcelain is examined. The effect of these oxides on phase formation and on the character of coloring of the structure on incorporation in the paste is examined.Underglaze painting is widely used as a type of decoration in many porcelain factories in the country. The palette of different underglaze colors is greatly limited by the fact that the coloring pigments can burn off or be reduced at high temperatures (1300 -1420°C) and in the reducing character of the gas medium [1,2]. For this reason, it becomes necessary to use high-temperature coloring compounds which are stable in these conditions. Rare-earth metal oxides (REMO) are such compounds. They can be used as components of paints for decorating porcelain articles and as a constituent part of the mass which has the property of coloring porcelain. Some properties and the color range of a series of REMO are reported in Table 1 [3].Coloring porcelain paste allows manufacturing porcelain for different applications: artistic, household, industrial, etc. One of the main problems in coloring the paste is giving the porcelain previously known coloristic and esthetic characteristics while preserving all of the properties of classic porcelain.The optimum amount of REMO (5.0 -7.5%) [4] was added to porcelain paste of the following composition (mass content, %): 66.21 SiO 2 , 21.12 Al 2 O 3 , 0.29 Fe 2 O 3 , 0.69 CaO, 0.47 MgO, 1.83 K 2 O, 0.85 Na 2 O, 0.13 TiO 2 , 6.31 calcination loss.The porcelain samples underwent microscopic analysis [5,6]. Petrographic analysis showed (Table 2) that incorporation of REMO in the porcelain changed its structure. With respect to the character of the effect of the REMO on coloration of the porcelain samples, they can be divided into two groups:forming crystal aggregates in the structure of the porcelain (Er 2 O 3 , CeO 2 ); not forming a crystalline phase but forming colored glass (Nd 2 O 3 , Pr 6 O 11 ).The boundaries of the pseudomorphoses with respect to feldspar are basically preserved and the size of the mullite needle network is 2 -10 mm, less frequently up to 15 -20 mm, the mullite in the basic paste is less than 1 mm in size, and aggregates are pronounced.All of the REMO alter the porosity and increase the amount of glass phase, manifested by perfection of the shape of the pores and slight improvement in the character of mullitization. Their effect is especially marked in blue porcelain containing Nd 2 O 3 (with respect to the structure, this is a porcelain of a normal degree of ripeness but with slightly larger pores).A possible cause of the appearance of isolated pores and sections of glass in incorporation of REMO is inadequate dispersion of the pigment in the paste, which can be eliminated by combined disaggregation of the components of the porcelain paste.X-ray phase analysis of the porcelain samples with REMO showed that CeO 2 forms an eutectic with mullite while Nd 2 O 3 and Er 2 O 3 forms the chemical compounds 2Nd 2 O 3 × 3SiO 2 and Er 2 O 3 × 2SiO 2 . An in...