Silver Coatings On Glass And Crystal Give That Extra Sparkle!

Rhinestones or chatons are coated with silver at the back to get that beautiful sparkle!

Silver Coating On Glass History

When people think about silver on glass then everybody thinks immediately about mirrors. In every housekeeping there are one or more mirrors like a bathroom mirror, every car is equipped with mirrors, mirrors are so common that we can't think a life without them.
Most probably the first mirrors used by people were pools of dark, still water, or water collected in a primitive vessel of clay or stone.
The first mirrors found in excavations, date back to about 8000 years ago. These were polished surfaces of natural materials. 
The first metal coated mirrors date back to about 100 BC in modern-day Lebanon and soon after that the Romans have been active with coatings of molten lead on glass and gold leaf on glass. 

In China they started coating glass with silver-mercury amalgams around 500 AD. When this technology came to Europe nobody knows exactly, (Marco Polo?), but the Venetian glass makers perfected this technology and around the 16th century, Venice became a center of mirror production using a thin film coating of tin-mercury amalgam on glass. Famous are the typical Venetian mirrors from that time which were a combination design mirrors with etched decorations .

Venetian style mirror

It took about three hundred years until the German chemist Justus von Liebig, invented a superior way to make mirrors and his invention of the silver on glass mirror stems from 1835. 
The process of von Liebig, involved the deposition of a thin layer of metallic silver onto glass through the chemical reduction of silver nitrate. The process could be done with the common chemicals, ammonia, caustic soda, glucose, water and silver nitrate and this was the main reason that the Liebig-process was quickly adapted for mass manufacturing. As a result mirrors became widely available and were affordable to everybody.

Mirror production today

The process of von Liebig, which makes a silver coating on glass, is still used but there are also other processes used in mirror manufacturing.
The ‘wet chemical’ process of von Liebig has the advantage that it is relatively cheap and it can be done by everybody. It is a simple technique and you can apply it for silverizing small series and for large quantities. 

Many mirrors in the house today, like bathroom mirrors and the mirrors in the living room, are made with aluminium as the reflectant. The difference between aluminium and silver is that aluminium reflects more the blue tones while silver reflects more red and yellow tones. This makes silver the preferred metal for making ‘cosmetic’ mirrors because they give a warmer image. 

The process to make a thin aluminium coating on glass is called PVD which stands for Physical Vapor Deposition. PVD is a thin film coating technique where first the aluminium is vaporized, then the glass object is put in a vacuum chamber and then the vaporized aluminium is led to the vacuum chamber and deposits on the glass, resulting i a thin film coating. 
The machinery to do this PVD is much more expensive than the ‘wet chemical’ process of von Liebig. On the other hand is aluminium much cheaper then silver and if you have large surfaces of flat glass to cover with a thin metal coating, then the PVD-process is the cheaper process. 

There are some other thin film coating techniques with which silver can be deposited on glass. The most used is the silver sputtering technique, basically the same technology as the PVD for aluminium. But this technique is mainly used for technical applications. The layer thickness can be controlled much better than with the ‘wet’ silverizing method and reflectors and mirrors, as part of machinery, are usually made by silver sputtering.
Xmas ornaments are examples of silverized glassware by the wet chemical method.

Silvering glassware

The wet chemical method or the von Liebig process) is the ideal method for silvering glassware and crystal ware
The most well known examples of glassware, made in this way, are Christmas ornaments.

For this process, two solutions have to be prepared: one silver solution and one reductor solution. By mixing these two solutions, metallic silver is formed and this silver then deposits as a thin silver coating on the glass surface.

Vases of all sizes, made from crystal or glass, can be easily covered from the inside, which gives the vase a very special look.
The easiest way to do this is by pooring the silvering liquids into the vase or any other glass vessel and shake until the silver forms an even silver coating on the glass. The chemistry can be adjusted to make the deposition of the silver quick or slow.

Silverized wine glasses, then color painted and as last step acid etched

Since a silver layer is very thin and vulnerable (also to the oxygen in air), it has to be masked. 
The brown coating at the back of mirrors is such a masking coating. This coating protects the silver from oxygen and scratching. 

When vases, lighting glass or drinkware are silverized, it is not nice to use this brown/red masking paint. It is then better to use a transparent masking coating.

Another way how to put a silver coating on glass is by spraying the two silverizing solutions. 
For this method two spray guns are used (each for one solution) and the chemistry is adjusted to make the silver forming process very quick.
The spraying is easy to automate and is widely applied in the glassware and  crystal ware industry.


Crystal Chatons

Silverized MC (Machine Cut) Chatons
The production of crystal chatons is a good example of a fully automated silverizing process by spraying. Chatons are the cut crystal jewelery stones or rhinestones which are used in jewelery, dresses, accessories, wedding dresses, etc. Many millions of these stones are produced every day and each piece must be silverized.

The chatons are put on a plastic plate in such a way that the front of the chaton is masked and the back exposed to the spraying. The plates are placed on a conveyor belt and so transported through the spraying booth. The first step is to clean the chatons and prepare them for the silverization. Next step is spraying the silverizing solutions and right after that a masking coating is sprayed on top of the silver for protection.
The silver coating in combination with the cut, lead crystal chaton gives an unbeaten sparkle. 

Consultant for silverizing chatons

The silverizing process for chatons or rhinestones is optimized for high speed silver forming and depositing. This process comes very precize and small deviations of the composition of the silvering liquids, the quality of the chaton surface, the impurities in raw materials, etc.,  can lead to a bad silver deposition.

I assist companies to start up with this process. For these projects I work together with a Czech company who has long experience of making state-of-the-art equipment for the silvering line for chatons. The silverizing line cost approximately 150,000 USD.

In this operation I am responsible for the chemical technology. So I will take care which raw materials you buy and where, optimize the settings of the silvering line, learn you how to do the trouble shooting.
In the end you'll have, for sure, a good adhered silver coating and a good color and brilliance.

If you want to discuss your silver coating on glass project with me and learn how I can assist you, then please Contact me.

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