In the initial segment of our discussion, we touched upon the fact that SIAMITE® glass-ceramic, created by Formica, is an entirely new type of gemstone imitation that did not exist before. Consequently, many people have question: what is the glass-ceramic?
Glass-ceramics are ceramic materials formed through the controlled crystallization of glass. Production takes place in two stages: in the first stage, a special high-temperature glass is produced using almost standard glass making technology, and in the second stage, this glass undergoes special heat treatment, during which nuclei and then crystals of minerals emerge. It is important to emphasize that crystallization occurs in the solid state (without melting), and the composition, size, and quantity of crystals depend on the initial glass composition, the temperature, and the duration of the heat treatment. This controlled crystallization allows the production of transparent (crystal size less than 10 nm), translucent (10–20 nm), and opaque (more than 20 nm) glass ceramics.
Clearly, the physical properties of glass-crystalline material significantly differ from those of the original glass. This breakthrough hybrid material combines valuable properties inherent in both crystals and glass, which cannot be found in glass or crystals alone.
Figure 1. (a) NOXTON glass-ceramic cooktop (www.amazon.com) (b) PYROCERAM glass-ceramic missile radomes (www.corning.com)
Glass-ceramics are developed and implemented in various fields of science and technology. They are used for cookware, electric stove tops, telescope mirrors, and missile randoms (Fig. 1). Their composition is highly variable depending on the application and the required properties. Many applications of glass-ceramics are based on their superior resistance to failure due to thermal shock. This particular property became the main reason prompting the author to extensively investigate existing types of glass-ceramics and choose the most suitable system for imitating colored gemstones.
So, the criteria for selection were resistance to thermal shocks at the melting temperatures of silver, gold, bronze, and other jewelry alloys (960-1200°C), relatively high hardness, density, and refractive index values, as close as possible to similar parameters in the most sought-after natural gemstones. Such a composition was found, and it will be discussed in Part 3.