Chemicals containing precious metals, such as gold, silver, platinum or palladium, play an integral role in the glass industry.
They serve not only for decorative purposes, but also to extend the life of glass and increase its durability. In what applications are they used?
Gold comes in several forms. How are they different?
Foil gold is packed onto the hot enamel before it is actually formed into the mould. Shiny gold is used in the form of an organic colloid that forms a shiny mirror when fired. The final form is polished gold, which is matt after firing and must be polished to achieve the required shine.
The addition of organic compounds improves the adhesion
As an inorganic salt, the glass industry mainly uses gold chloride (AuCl3), which is produced as a yellow-brown liquid or as a crystalline substance that is extremely hydroscopic. It is used to decorate glass with shiny gold and in the process is converted into gold mercaptide, which is a brow-black viscous liquid whose odour does not escape our noses.
This gold would form a gold mirror on the glass, but the adhesion of the layer to the surface of the glass would be very slight. Therefore, organic compounds of metals and non-metals are added to the mixture, which chemically bond with the gold and at the same time form an interlayer with the surface of the glass. Furthermore, organic substances in the form of essential oils (rosemary, lavender, benzene or turpentine) are added to the mixture, which act as diluents and homogenizers and dampen unpleasant odours.
Silvering the glass around us, for example in mirrors
Other widely used chemicals containing precious metal include silver nitrate (AgNO3), an ammoniacal solution of which is used to silver glass. At present, manufacturers supply two solutions for silvering glass, which are mixed in a specified ratio before the actual silvering. This mixture has its inherent place in the production of glass Christmas decorations or in the manufacture of mirrors. Other applications include the production of heated car glass in the automotive industry.
Silver glaze for beauty and functionalit
Other silver compounds, such as silver oxide (Ag2O) or silver chloride (AgCl), are used in the production of silver stain. The latter was formerly called silver yellow and was used by painters in the Middle Ages to decorate and enhance the durability of cathedral windows. The glazing produces a yellow layer with considerable chemical and mechanical resistance.
The yellow coloring of the glass surface with silver can only be obtained by glazing; coloring transparent enamel with silver during glass melting is not possible.
Silver chloride (AgCl) is the basic raw material used in the Lithyalin glass decorating technique, which was discovered in the 19th century by Bedřich Egermann.
Last but not least, silver sulfate Ag2SO4 is also an important representative, which is one of the basic raw materials for the production of pearlescent glazes, which have found their application mainly in the ceramics sector.
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