Frit is one of the major constituents of ceramics, particularly in the engobe and glaze layers. Frit, a ceramic glass, is predominantly composed of silicon dioxide and other oxides depending on its intended use. The raw materials of frits are fused at high temperatures and rapidly quenched to form resistive and insoluble glassy granulates. The intended role of the frit in ceramic products is to lower the softening temperature, reduce the permeability of the tile body, achieve cleanability of the surface and offer glossy aesthetics to the final product. However, the production process of frit is energy intensive and expensive; also, its raw material is of natural origin. Industrial energy efficiency has been in the spotlight during the 2022 energy crisis, which necessitates focused studies to overcome unstable energy prices and unreliable supply-related issues. Considering the huge market of ceramic products and its growing demands over the years, partial or full replacement of frit from the ceramic industry is of high interest concerning the benefits of lowering environmental impact. The study aims to develop a frit-free glaze formulation with the possibility of in-situ development of a eutectic glass ceramic phase during the firing process of the ceramics using sustainable alternatives without compromising the quality of conventional ceramic products.

A standard industrial glaze formulation was modified with alternative raw materials by replacing frit with recycled borosilicate glass and recycled soda-lime glass, quartz with chamotte, and kaolin with metakaolin, respectively. A systematic experimental approach based on Mixture Design by Design of Experiments (DoE) was adopted in opting for mixtures with varying replacement levels of selected (based on the preliminary screening) alternative raw materials. A total of 20 mixtures were chosen for the detailed study. Specimens of each mixture were prepared at laboratory and industrial conditions to eliminate any variations in kiln firing conditions. The measured responses or output factors selected based on the industrial interest from different glaze formulations were: (i) cleanability after interaction with methylene blue dye, (ii) coefficient of linear thermal expansion, (iii) colour difference between the standard and modified glazes, and (iv) softening temperature. The results were analysed, optimized, and validated using statistical techniques; selected formulations were further characterized using a TG- DTA thermal analysis, and the best glaze formulation was derived. The obtained frit-free glaze composition with secondary raw material is considered to be a sustainable and energy-efficient solution for the ceramic manufacturing industries.