Vapor Deposited Aluminum Plating

Originally auto headlamp reflectors were plated with silver. Which makes sense as it is one of the most reflective metals. But it does have drawbacks – it’s expensive and it tarnishes over time. As a result, the modern process used by all automobile manufacturers is vapor deposited aluminum plating. A very thin layer of aluminum is deposited on the substrate and then protected by a coating of silica.

Aluminum is less expensive and does not tarnish over time – and it’s almost as reflective as silver.

I’m sometimes asked why I go to all the trouble to have the reflectors restored with vapor deposited aluminum as opposed to simply chroming them. Chroming is a lot simpler as the process can be done a single plater as opposed to aluminum which requires having the reflectors prepared by one plater – copper -> nickel -> polishing – then sent to a second plater for the vapor deposited aluminum process. Also, it’s much cheaper to just chrome plate them and admittedly the aluminum process is more expensive and with more moving parts, which takes longer..

The reason? Chrome just doesn’t work very well. Using silver as the standard for reflectivity, vapor deposited aluminum is 95.6% as reflective as silver, while chrome is 63.5% as reflective as silver. You lose almost 1/3 of the light with chrome as opposed to aluminum. Here are the numbers:

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Reflectance Comparison
Silver: .95512 = 100%
Aluminum: .91320 = 95.6%
Chrome: .60604 = 63.5%

Source:
Refractive Index
http://refractiveindex.info/?shelf=main&book=Cr&page=Rakic

The central point of H1’s is their shear brilliance. When done right they are flame throwers. It kind of defeats the purpose to decrease the light by a third with chrome plating. My goal is to restore H1’s to as high a level as possible and vapor deposited aluminum, the process used by all modern automotive manufacturers, is the best way to go at this time.


flying a© 2015 ~ Audette Collection ~ Bend, Oregon
H1, H4 and SWB Turn Signal Concours Restorations ~ Email

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