Different techniques (chemical analysis, X-ray diffraction, Mössbauer spectroscopy, UV-Vis-NIR spectrophotometry and chromaticity measurements) were used to study the color variation of feldspathic raw materials after firing at 1200 °C. Two varieties of feldspar-quartz grits (with Na₂O or K₂O prevalence) doped with synthetic pigments (hematite and rutile) were heat-treated in an oxidizing atmosphere. The results obtained indicate that the color of the ceramic body after firing may not only depend on the presence and analytical content of coloring elements (such as iron and titanium), but on their valence state and the chemical characteristics of the melt itself. The prevalence of larger alkali K⁺ ions over Na⁺ ions may cause the reduction of the coordination number of iron. This has a significant effect on the length of the Fe–O bond, which in turn influences the capacity for light absorption of a specific wavelength. The results of spectrophotometric measurements showed pronounced disparity between the raw materials and samples doped with coloring oxides. The introduction of synthetic pigments caused clear changes in the spectral dependence of the total absorbance. The absorbance increased in the whole measuring range, in particular in the visible part of the spectrum. Furthermore, a red-shift of the absorption bands towards longer wavelengths attributed to oxygen-metal charge transfer (OMCT) interactions between Fe³⁺ and O²⁻ ions as well as to d-d transitions within Fe³⁺ ions was observed.

中文翻译：

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煅烧后长石-石英原料的研究：各种Na2O / K2O比和合成颜料添加的影响

在1200°C煅烧后，使用了不同的技术（化学分析，X射线衍射，穆斯堡尔光谱，UV-Vis-NIR分光光度法和色度测量）来研究长石原料的颜色变化。在氧化气氛中对两种掺有合成颜料（赤铁矿和金红石）的长石石英粗粉（Na ₂ O或K ₂ O普遍存在）进行了热处理。所得结果表明，烧制后的陶瓷体的颜色不仅取决于着色元素（例如铁和钛）的存在和分析含量，还取决于它们的化合价态和熔体本身的化学特性。较大的碱金属K ⁺离子在Na ^+上的普遍性离子可能会导致铁的配位数减少。这对Fe-O键的长度有重要影响，进而影响特定波长的光吸收能力。分光光度法测量的结果表明，原料和掺杂有着色氧化物的样品之间存在明显的差异。合成颜料的引入导致总吸光度的光谱依赖性发生明显变化。在整个测量范围内，特别是在光谱的可见部分，吸光度增加。此外，吸收带的朝向归因于氧金属的电荷转移（OMCT）铁之间的相互作用较长波长红移³⁺和O ^2-离子以及以铁内DD转换³⁺ 观察到离子。