The opacification of enamel frit is a dispersed system formed by glass matrix and opacity particles, the matrix is the dispersion medium, and the opacifier is the dispersed phase. Since the refractive index of the opacifying agent is different from that of the matrix, when the light enters the porcelain layer, it will be scattered or diffusely reflected, causing the light to fail to reach the ground coat and devitrify. This phenomenon is the opacification of the enamel.

The degree of opacity generally increases with an increase in the number of opacifying particles and a modest decrease in diameter, due to the increase in surface area that results in diffuse reflection of light. However, if the particle size difference between different crystals is too large, while obtaining sufficient opacity, its gloss will be reduced. Only when the crystal particles are uniform and fine, and the number is large, can the enamel not only have a strong opacification ability, but also improve the gloss of the porcelain surface.

The degree of opacity also has a great relationship with the thickness of the porcelain layer. Taking titanium enamel and antimony enamel as examples, their opacity initially increases with the thickness of the porcelain layer, and when the thickness of the porcelain layer reaches a certain value, it hardly changes. For example, when the thickness of the titanium enamel layer is 0.1mm, the reflectivity can reach 82%. At this time, if the thickness is increased, the reflectivity will not be greatly improved. For antimony enamel and zirconium enamel, in order to achieve higher opacity, the thickness of the porcelain layer is much thicker than that of titanium enamel.

The degree of opacity is also related to the chemical composition of the enamel, namely the base formula and the introduced opacifier. For example, the introduction of P2O5 and AS2O3 into the titanium enamel formula can promote the precipitation of more anatase crystal forms when the product is fired, especially P2O3 is more beneficial to the precipitation of anatase crystal forms.

CaO and fluoride in antimony enamel are beneficial to the crystallization of Sb2O5. When the antimony enamel is melted and the product is fired, Sb2O5 will continue to crystallize and separate out. Therefore, the frit of antimony enamel is different from titanium enamel, which is devitrified.

The opacity of enamel is related to the melting process. In particular, the titanium enamel must be fully melted within a reasonable temperature range, so that TiO2 can be dissolved in the glass as much as possible, so that a large amount of TiO2 crystals can be precipitated during firing. If the melting temperature is too low or the time is too short, TiO2 cannot be fully dissolved and the emulsification is reduced.

This is not the case for antimony enamel. With the increase of melting temperature or the extension of time, Sb2O5 in antimony enamel will be reduced to Sb2O3, which will reduce the opacity.