Silvering



Silvering is the chemical process of coating glass with a reflective substance. Glass mirrors were first coated by molten metal. Later, sputtering, powdered aluminium or other compounds are more often used for this purpose, although the process maintains the name "silvering".

History

In the early 10th century, the Iranian scientist al-Razi described ways of silvering and silver, and deposited onto the glass. Then in 1880, American astronomer John Brashear improved the process in order to make more powerful and accurate telescopes. These techniques soon became standard for technical equipment.

mercury have historically been used in the silvering process.

Modern silvering process

In modern aluminum silvering, a sheet of glass is placed in a vacuum chamber with electrically heated nichrome coils that can sublime aluminum. In a vacuum, the hot aluminum atoms travel in straight lines. When they hit the surface of the mirror, they cool and stick. Some mirror makers evaporate a layer of aluminum oxide.

Mirrors made by this method are classified as either back-silvered, with the silvered layer viewed through the glass; or front-silvered, with the layer viewed from the other side. Most common mirrors are back-silvered, since this protects the fragile reflective layer from corrosion, scratches, and other damage. However, extraneous reflections from the front surface of the glass make these mirrors unsuitable for high-precision optical work.

See also

References

  1. ^ Annalen der Chemie 14 (2): 133. doi:10.1002/jlac.18350140202.
  2. ^ Annalen der Chemie und Pharmacie 98 (1): 132-139. doi:10.1002/jlac.18560980112.
 
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