Of unquestionable beauty, marco-crystalline glazes are fascinating, perfect! Products of fire and alchemy.
The magic of this process produces a crystal on the high temperature liquid glass - it's just a glass layer. They can be colorful with delicate shapes, almost magic, and transcend mere technical expectations. A glassy glaze with crystals stimulates imagination.
A crystal's growth begin with the development of a crystalline "seed" or nucleation spot, a tiny mineral grain where the macro-crystal will be formed - it's born inside a glass with a chemical logic, liquefied by the high temperature. The crystals are formed in a process of heating and cooling down - temperature and pressure - their positions and sizes never repeat. The molecules move randomly, tridimensional molecules organizing themselves to imitate nature.
They are very special and unstable glazes, of unexpected effects, which we can't exactly reproduce.
The crystalline formations can be round like flowers, sharp like needles, varying temperature.
It's a glaze that surprises us everytime we open a kiln. Sometimes a great crystal pops from within a group of tiny jewels, often quite shiny, often opaque. There can be also no crystal.
There's no way to totally control the crystals growth and that makes the job much more exciting. Even if a firing is exactly like the other, everything can turn out diferent each time.
Some people say crystalline glazes already existed in the 21th century in japanese and korean glazes like Oilspot and Kaki. In the early 1800 those were considered fire acidents and of no interest, because the loses rate was too high.
In Europe early 19th century is mentioned in Sevres - France. At the beginning of the 20th century, those glazes with effects rejected by the ceramic industry start to be developed by ceramic artists in their studios. These ceramists/alchemists surprised the world with works, then contemporary and of rare beauty, having their pieces bought by museums and collectors.
Perseverance and patience are part of everyday of the ceramist who dedicates to this art. Very special moments appear along this dedication, some of great joy, mixed to those of disappointment. However, small changes can have deep effects in the next firing's result.