Headlight reflector plating

Prior to sealed beam lamps, most headlight reflectors were brass with a colorless reflective plating. What was it?

Bill

Silver. I had the reflectors on my model T redone at a silversmith's.

kinda OT but over here, like europe, there never was sealed beam headlights. one '80s car i had was missing the rubber boot that sealed around the bulb allowing water and grime to get in and corrode the reflector. at the yearly inspection it caused me to fail and i was told to replace it....so i gingerly cut the rubber seal holding the glass in place, cleaned up the reflector with scotchbrite, laid down a bunch of rows of that bright aluminium backed tape, burnished it down with a big rubber eraser, then glued the glass back in place. back at the inspection garage they put the testing machine in front of it and to my surprise it passed.



dave

I cleaned up the reflector with a small wire brush through the bulb hole and used aluminium paint to repair the affected areas. This is not a permanent fix, but it will get you through inspection.

If you happen to know anyone who has a large vacuum chamber you can sputter
or thermally evaporate aluminum for this application.

Not that I've ever done that, of course....

Jim

Apparently the model T used a very polished substrate with nickle or stainless. Telescopes are glass substrate with aluminum (very slightly less reflective, but reflects all colors in the spectrum more evenly) or silver (a bit more reflective, but easier to tarnish).

J

As I would expect, an interesting set of answers. I have silver and nickel plating, so either is a good possibility, but the next question is what did they coat the plating with? When bright nickel comes out of the tank it is almost white, but you have to rinse and blow the water off very quickly because nickel passivates while you watch, changing to a yellow cast. Silver takes longer to tarnish, but it will turn black. I think the modern solution would be to wipe silicone grease on the surface immediately. I have an 18" dia vacuum chamber and have played with aluminizing a bit. Putting the coating on is simple, but it depends on good surface preparation to make it stay on. Telescope mirrors are coated with silicon monoxide, which I suppose is evaporated on at the same time. My silver doesn't have brighteners since it is done for electrical contact purposes, so I will probably use nickel. A silicone coat will probably do the job, but they didn't have silicones back then.

Thanks for the suggestions.

Bill

Bill,

For fine optics, the solution is to coat with a MgF2 coating. If you were to take this to someone who does Al coating for telescope mirrors, they could probably do it.

It may be overkill, and your nickel plate, with appropriate coating, might do just as well.

Jim

I don't think you need the SiO for a headlight reflector.

Aluminum self-passivates with about ten angstroms of Al203 the instant
you get it out of the system into air. Depending on your surface that you
are starting with, you might put down an adhesion layer like Ni, or maybe Ti
but I suggest you clean up the surface as much as possible, and polish
it as well. Then just give it an alcohol wipe-down and coat.

If you have adhesion problems you could consider the Ni or Ti.
Jim

To widen the horizons of this discussion, I'll add that at least one outfit aluminizes headlight reflectors and then coats the aluminum with a thin layer of glass. Considering the amount of work it takes, it is quite affordable.

We have a fleet of antique Model A Fords and all of them have been equipped with aluminized headlight reflectors. They are noticeably brighter than the original silvered reflectors.

Orrin

but the next question is what did they coat the plating with?

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My Model A reflectors are silver plated. There is no coating on the surface. As long as you don't touch the surface they stay untarnished for quite a while. Every once in a while (5 years or more), we'll dip them in tarnex and their good to go for quite a while longer.

Pat Black

Orrin,

Who can carry out this process? I have Lucas lamps I am restoring for a 1934 British sportscar.

Jim

I Googled silicon monoxide and got a lot of hits. It comes in granular form, so you probably use platinum boats to evaporate it. The aluminum is really easy, just hang pieces of Al wire on a tungsten filament, pump the chamber down, and light the filament. Silver also evaporates nicely. I have never done it deliberately, but doing vacuum casting with silver, the surrounding area gets coated.

I wonder if I could get enough of this business to be worthwhile. Like a lot of people's, my business is in the tank. Since I already have the equipment, it gets into "anyhow economics". You have the shop anyhow, equipment anyhow, and I have way too much free time anyhow. Most of the work would be polishing the bad reflector.

Bill

SiO is a standard E-beam passivation. But honestly, aluminum forms
its own passivation, aluminum oxide, which is very tough and self-healing.
I doubt that you really need any coating like this on top of aluminum, or
any AR coating like MgO.

Jim

Orrin said:

To widen the horizons of this discussion, I'll add that at least one outfit aluminizes headlight reflectors and then coats the aluminum with a thin layer of glass. Considering the amount of work it takes, it is quite affordable.

We have a fleet of antique Model A Fords and all of them have been equipped with aluminized headlight reflectors. They are noticeably brighter than the original silvered reflectors.

Orrin

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Who is that? I need some done.

jim rozen said:

If you happen to know anyone who has a large vacuum chamber you can sputter
or thermally evaporate aluminum for this application.

Not that I've ever done that, of course....

Jim

Click to expand...

Well, yea I DO.......

Vergason Technologies in Spencer, NY

http://www.vergason.com/about.php

They do the plating and build the machines to do it

dk

About the hardest part of sputtering a reflector with aluminium is leaving it in the vacuum long enough to outgas properly if ion bombardment isn't being performed on it.

With glass telescope mirrors it's considered well done if it passes the sticky tape test where applied scotchtape doesn't peel off the aluminium with it off the glass surface. If it doesn't pass then your coater didn't clean the reflector properly as this takes time and is expensive to do.

Personally I'd be inclined to spin up a new aluminium reflector on the lathe and then hand polish it as required, no coating is necessary as it will self oxidise to form a coating as others here have mentioned and you may have a nice new sideline selling extra reflectors to other restorers.

dkmc, As I said earlier, I have an 18" dia chamber complete with fore and roughing pump, 6" diffusion pump and LN trap, thermocouple and ion gauges, another case of your tax dollars at work. The US Navy bought it for Washington University, judging from the crud in it, for silicon research. It worked its way through the University and finally passed into my hands. It has high current water cooled feedthroughs that I have put as much as 800 amps through. I use it a lot for things like vacuum heat treating and brazing. Changing to vacuum coating would just be a matter of adding the filaments, boats, or whatever.

Jim, the aluminum self passivates, but that isn't enough protection against someone who cleans the reflector with a paper towel. Aluminum will also corrode in a humid environment.

SAG 180, My spinning is pretty rippled and has stretch marks, so it would take some serious polishing.

In a previous incarnation I designed spectrophotometers and made experimental mirrors, usually concave, from solid aluminum. We polished then on a honeycomb foundation lap with 1 micron synthetic sapphire from Micro Abrasives. We always had a pattern of fine scratches, although they were not enough to seriously affect the experimental results. We tried .1 micron abrasive, but were never able to prevent clumping, which left shallow marks like you had dragged a fingernail on them. My boss, who was an insufferable SOB, kept telling me how stupid I was because before glass mirrors, all astronomers had was speculum metal and they got them polished somehow. When I had all I could stand of him, I quit and went on a tour of Europe. In the Science Museum in London I saw Lord Rosse's diagonal with exactly the same scratches. I guess they just put up with them.

A month or so ago, I got a call from a Washington U. Medical School grad student. He was working on an eye tracking system to follow a subject's eye movements during tasks. They were using infra red to avoid distracting the subject and the mirrors they were using lost the signal. I told him to hold a mirror up to a bright light. He said he could see red light through it. I pointed out that he could see the light, it wasn't being reflected- duh. Someone must have gotten the spec backwards and given them mirrors with a dichroic coating that transmitted IR. Sometimes I think God made grad students just to give the rest of us a laugh now and then.

Bill

Orrin,

Who can carry out this process? I have Lucas lamps I am restoring for a 1934 British sportscar.

Jim

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The outfit that does the aluminizing is in Oregon, but you will need to contact Triple Plate Chrome in Spokane, Washington, and have them do the preliminary work. You should be able to do a Google to get Triple Plate's address and telephone number.

Triple Plate does the polishing and applies a nickel layer. Then, they send the reflectors to Oregon.

It's a long story, but the Oregon people once did all the polishing, etc., but for reasons too complicated to explain, they don't do it, any more.

If you have any trouble getting in touch with Triple Plate Chrome, let me know and I'll lend a hand.

Indeed, aluminum forms its own passivation layer, but the aluminum oxide is not as reflective as freshly applied aluminum. That's the reason for the glass. The people who do this work know all about self-passivation, but they also know more of the fine points of reflectivity than the most of the rest of us.

Orrin