The first stage is the raw materials. The basis for the manufacture of ceramics are natural components, time-tested: clay, sand, minerals. However, the extraction of raw materials takes place in quarries, so manufacturers must take into account the radiation background. Raw materials undergo strict anti-radiation control before baking.
The raw material is then checked for the presence of metals by putting it through a magnetic filter. Kneading, shaping and firing usually does not contain any pitfalls.
The next step is the application of the glaze. The compositions of glazes cause a lot of controversy. Many believe that only earthenware is environmentally friendly, and any glaze is harmful. Let’s try to figure out if this is true.
The basic composition of glazes consists of quartz, alumina, calcium, boric acid. Also the constituent components can be oxides of different metals: sodium and potassium, strontium, lithium, magnesium, zinc, tin, zirconium, titanium. Oxides of iron, cobalt, copper, chromium, manganese, and nickel can be used as coloring components.
The trick is that these oxides are only harmful if inhaled. After high-temperature firing, they become safe because they are not released, leached or leached out of ceramics in any way.
This is not the case with oxides and chromates of metals such as lead, cadmium, barium, antimony and arsenic. They can leach out of the fired glaze when utensils are used for foods containing acid: kefir, vinegar, and fruit juices.
For a long time, they were used to produce matte surfaces or bright stable coloring pigments. In countries with a rich history of ceramics, much effort has been expended to get rid of harmful impurities in glazes and replace them with safe alternatives.
In conclusion, it should be added that ceramics are fireproof. In the case of fire or a sharp rise in temperature, ceramic coatings do not release toxic substances into the environment. It is not without reason that our ancestors have been using this material for centuries to furnish their homes and cook food.