The manufacturing process of smalt is based on glass technologies in open gas furnaces with a temperature of more than 1200 degrees C, with subsequent adequation of stresses by controlled cooling in muffle furnaces.
Smalt is an opaque (visionproof) silicate glass, painted with oxides of various metals. Like any other glass, it is brewed from the main and auxiliary materials. The main materials are quartz or high-purity quartz sand, potash (plant ash, fern, beech) and soda. Initially, the materials are prepared and cleared from impurities that affect the quality of glass.
The use of powdered glass is eliminated, which ensures a high homogeneity of the material, and simplifies the machining process of the material. Smalt has a silicate base and components from certain fields are used for its synthesis.
The compact structure without pores, which does not allow moisture to penetrate into the material, provides the possibility of long-term use of smalt under practically all conditions, including high humidity (swimming pools, building facades), vibrations (underground), etc.
The main advantages of the material:
- Smalt can be cut in any direction, unlike natural stones, the structure of which allows the material to be cut in only one direction.
- Using in any conditions
- Color is distributed throughout the volume, so you can work both with the surface and with the inner face (for splitting).
- Sawing with a regular glass cutter into fragments of a given geometric shape.
- The palette has more than 1000 shades.
- The ability to synthesize additional shades.
The process of making colored smalt contains several stages:
– a glass alloy production;
– milk glass (an opaque or translucent glass) manufacturing;
– the main colored alloy production – alloying the milk glass with dyes;
– melting of smalt.
1. Preparation of the feedstock.
The feedstock is a homogeneous mixture of materials that were previously prepared and weighed according to a given recipe. The feedstock should be indiscrete. The ratio of raw materials should be the same and correspond to the specified composition. The main conditions for manufacturinga properly prepared feedstock are the use of enriched and prepared ingredients, the accurate dosage, the thorough mixing till a complete homogeneity and the supplying and loading, excluding the possibility of its delamination.
2. Melting of smalt.
The open gas single pot glass-melting furnace is used for the melting of smalt. The method of production is ladling.
White smalt is produced (картинки 3,4) by sand and ash melting. Smalt is melted in monkey until the composition becomes liquid as a glue, and when the mixture of ash and sand is welded, then it is ladled. it is melted till it becomes completely white. Milk glass (an opaque or translucent glass) is produced by melting of quartz sand, refined potash, lime, saltpeter, arsenic, and flake white.
The most valuable feature of smalt is its wide color palette and the possibility of almost any color reproduction. It happens due to the incorporating of dyes in the main structure. Substances that are used in dying should be stable while flashing. The richest palette is possessed by substances calcined at temperatures not higher than 800-850°C. With an increase of the flashing temperature, the palette of resistant dyes becomes more and more narrowed, therefore, the palette with the flashing temperature of 1400°C is very limited.
The staining of the glassy masses is usually created by the dissolving of dye ions in the glassy phase, as well as by dispersing of colored particles in the colloidal or solid phase, like with the opacification.
Coloring depends on the nature of the dyestuffs injected, on the chemical composition of the glass mass and on the firing conditions.
After melting the smalt is poured and slowly cooled in the oven (the second stage is an electric furnace), which gives considerable hardness to the smalt glass.
3. Smalt’s tiles manufacturing
The tiles are taken out of the oven at a certain temperature, stretched to the desired shape and thickness, and then tiles are cooled.