High temp light diffusing paint?

I have metal halide fixtures that have a clear glass. I would like to make some sort of a light diffucing glass and am curious if there are any paints or coatings that stick to glass and are white and diffise light.
Something like chalk paste or some such (which I can make myself in a blender if it is suitable).
i
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You will increase the fixture temperature perhaps to unsafe levels and reduce output, the temp is hot enough to cook on the glass
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You have to be very careful - even clear glass gets quite hot in such a fixture and by changing the glass you probably have to re-do UL qualification etc.
That said, the keyword you want for diffusion in such a fixture is "frosted" or "prismatic". Glass remains clear but is cast (prismatic) or sandblasted (frosted) in such a pattern that internal reflection/refraction takes care of diffusion.
Tim .
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If you want a reflective white diffusing coating, the standard optical product is called "Munsell White Reflectance Coating". It's real good stuff and easily coated onto glass. I suspect you're talking about a transmissive diffuser, though (the other side of a piece of glass coated with this stuff will have only a tiny fraction of a percent of light shining through!)
And a colleague who used to work in the lighting industry informed me that most frosted glass used to be done with hydrofluoric acid etching, although he was of the opinion that this is seen as environmentally unfriendly today.
Tim.
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Yes, I want diffusive coating, not reflective.

I suppose I could rig something up to blast glass using my compressor, but I was hoping to just find some coating.
i
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On Wed, 07 Dec 2005 16:51:04 GMT, Ignoramus8325

You can't just sand blast it?
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I do not have a sandblasting setup of any sort, presently.
i
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On Wed, 07 Dec 2005 18:05:43 GMT, Ignoramus8325
You know, if you and I lived a bit closer, I could see us hanging out together regularly. I've got a blast cabinet in the garage...
One thing to think of - around here we have an outfit called "U-Spray" which rents sandblast cabinet time by the minute. Inexpensive, they have all the equipment, and you just pay a flat fee based on your time. Might be a franchise?
Dave Hinz
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mount the light facing up so it diffuses off of the ceiling...
that makes for a much gentler light
Mark
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http://www.lonestarts.com/DripPan/SandBlaster.htm
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At least from my own experience with MH fixtures, there's a good chance the glass is tempered, designed to protect you from excess UV and from showers of nearly-molten quartz if a bulb ever detonates. I would not mess with the factory glass.
How hot does the outside of the glass get?
I used to have an MH in my garage that was a high-bay fixture in a lower-height room, so I put an external diffuser on it, just cut a circle out of one of those plastic diffuser sheets you can get at the hardware store for 4-tube fluorescent fixtures, and mounted the circle an inch below the MH fixture's glass.
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When I wanted frosted glass in an outdoor lamp fixture I frosted it with a palm sander and aluminum oxide paper (I think.) it was a long time ago. Maybe emery paper. I would think 80 grit would be about right. Tom

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wrote:

Thanks... I have a belt sander...
i
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Frost it and you will retain heat and possibly do damage, talk to a manufacturer of fixtures or bulbs.
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Add a piece of frosted glass. Frosting your glass can weaken it and MH fixtures need a sheild in case of "non-passive failure."
There are some theatrical materials that come in a wide range of frostings and colors. If the heat isn't too great they would be ideal.
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Just go to a craft store and get some mirror etch for etching mirrors. It does a nice job of frosting the glass. It is a paste acid etch of some kind. Glenn
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