We had a good opportunity to compare the performance of our gold coated copper mirrors with uncoated copper mirrors recently. A customer sent us dozens of large water cooled mirrors from his 6KW CO2 laser to re-manufacture. The workplace environment of the laser cutting system had dulled and corroded the bare copper mirror surfaces. Simply handling the mirrors had caused stains on the mirror face. In comparison a gold coated mirror, from exactly the same laser, had barely changed it’s appearance, or performance.
We’ve also recently helped customers in tropical climates who had problems with copper mirrors corroding, even in storage. Moisture reacts with exposed copper to cause pitting and staining, and even penetrates through pinholes in dielectric coatings. Several OEMs are now specifying mirrors should be Electroless Nickel plated, so no part of the mirror is exposed copper. This is already the case with all of LBP Copper mirrors. Copper can also diffuse into metal mirror coatings deposited on it; to prevent this a diffusion barrier such as Electroless Nickel should be used.
Some of our competitors are now warning that copper mirrors should be kept absolutely dry, which is simply impossible if they are to be used. Especially as most of them are water cooled!
There is more information about Electroless Nickel coating of mirrors on our website