If you have a multi color log there are some companies that can put it on a glass gobo. It's a lot more expensive though. Rosco is probably one, there should be others.
If I recall correctly Nino talks about an attachment for the source 4 that allows you to print your own on transparancy media for one time use type things.
Now that I have checked it is the rosco image pro
That's true. Inkjet transparencies are designed to hold up to having high wattage overhead projector lamps hitting them. They won't last a long time, but they also aren't as expensive and replacements can be printed as necessary. It's a pretty ingenious add on for the ETC lights.
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