Automated Fixtures DIY Glass Gobos

z2oo

z2oo

Active Member
I'm curious as to what you all think about the adventure I might be going on in the near future...

Basically, I'm interested in having the ability to create custom glass gobos for moving lights. I've found disks of glass from McMaster that can stand a max temp of 445° in the right size, and plan on essentially screenprinting a design on with grill or engine block paint (something high-temp and opaque). I'd love to know if it seems like I'm a crazy person for doing this, what issues you might see with this thought, and any other comments or questions anyone might have. This isn't show critical by any means, but it seems like it's much cheaper to spend $95 for 12 pieces of glass than potentially that amount for 1 custom made gobo. So, what do you think?
 
Gate temperature of a Source Four at 575w is about 600°F best case scenario, in a 750w 900°F at worst case.

Think you'll find that 445°F doesn't get you very far in any moderately sized ML.
 
What’s the paint rated for.
 
Amiers said:
What’s the paint rated for?
Click to expand...
@Amiers Kodak, remember them, the company that made film, cameras and projectors in Rochester? Back in my 35mm slide projection days, Kodak used to market a paint sold as "Opaque black", you painted it on any pin holes in your black slides and any leaky spots in your Koda-lith title slides. Koda-lith was a film with zero contrast ratio; it was either clear, unexposed, or opaque black, exposed. you could purchase it in normal 24 exposure rolls or in longer lengths, 100' put-ups are coming to mind. It was great for shooting title slides and you kept your little bottle of opaque black paint with it for touching up any imperfections. The Kodak opaque black paint was designed to withstand life in the gates of projectors.
Toodleoo!
Ron Hebbard.
 
RonHebbard said:
@Amiers Kodak, remember them, the company that made film, cameras and projectors in Rochester? Back in my 35mm slide projection days, Kodak used to market a paint sold as "Opaque black", you painted it on any pin holes in your black slides and any leaky spots in your Koda-lith title slides. Koda-lith was a film with zero contrast ratio; it was either clear, unexposed, or opaque black, exposed. you could purchase it in normal 24 exposure rolls or in longer lengths, 100' put-ups are coming to mind. It was great for shooting title slides and you kept your little bottle of opaque black paint with it for touching up any imperfections. The Kodak opaque black paint was designed to withstand life in the gates of projectors.
Toodleoo!
Ron Hebbard.
Click to expand...

The paint I'm looking at is rated for 1200°, so I feel like the temp of both materials should be ok. I'm going to have to experiment and see how things go!
 
If you want to give it a try, I would do a trial run and park a fixture down on a workbench, tilted so it's parallel with the floor, and run a sample for 12 hours. Then if you shatter anything it's not going to get pulled into the gears, nooks, and crannies of the fixture and be a mess to clean out.

Concept may work for breakups and such but I would expect to see issues with sharpness, straightness of edges, and such that would make it impractical for anything of any importance like logos. Wouldn't be surprised if the paint doesn't adhere very well to the glass or just generally that either the images or the glass doesn't have the longevity of a professionally built gobo.

I would also be concerned about any fumes given off baking the paint that may irritate audience members.
 
I think the problem of differential expansion--between the black and clear areas--of the glass would be a problem unless you use a glass with a super low coefficient of expansion, such as the stuff used for the tops of glass-top electric ranges.
 
As previously mentioned, I'd be very concerned with fumes. Make sure you run it for a few hours with the covers off, and in a very well ventilated area when you start off with a pattern. Post some pictures if you get something to work. One of my guys has experimented with various options similar to this, but never really got a good result.
 
You won't be happy if you're looking for accurate, fine details. Remember that you're making something very small that will be magnified many times, so tiny flaws will be much more visible in actual use. I've made some metal gobos for conventional fixtures using a toner-transfer etching process. It's fine for a breakup that will be slightly out of focus anyway, but it's very difficult to get crisp images.
 
I did something very similar with some high temp science lab Pyrex and some ceramic muffler paint (also1200). It worked, but after a few nights there was flaking. The paint was intact, but adherence was an issue. I can’t speak for fine designs, since I was using it for a Kabuki play, painted the glass black, and had a Japanese friend write kanji characters negatively with a toothpick.

This was 20 years ago- nowadays I would just project it-
 
Uncle Dirtnap said:
I did something very similar with some high temp science lab Pyrex and some ceramic muffler paint (also1200). It worked, but after a few nights there was flaking. The paint was intact, but adherence was an issue. I can’t speak for fine designs, since I was using it for a Kabuki play, painted the glass black, and had a Japanese friend write kanji characters negatively with a toothpick.

This was 20 years ago- nowadays I would just project it-
Click to expand...
I used to make hundreds of gobos this way. This was back when the Sourcefour was a new concept. The heat reflecting dichroic reflector reduced gate temperature dramatically. I used grey barbecue spray paint. Same as mentioned above . Use Borosilicate glass, 1/8" thick and swipe the edges of the disc on a belt or disc sander. This relieves stress on the glass. Clean the glass with isopropyl alcohol before spraying the coating.

I did not screen print the blank glass. I sprayed it with several very light coats. I then put the coated parts in a 20 watt CO2 laser engraver. Through experimentation, I found the right power level to erase the paint and not craze the glass substrate. Took about 30 seconds to make a B-size gobo. Back then, my laser cost $30K Now you can get a small table top unit for about $1600. Then again, you can buy a 4000 lumen DLP projector for about................. $1600. Time marches on
 
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