These are 35mm GOBO slides. I created these to use in a Spiffy Gear Light Blaster but the 35mm size allows you to use any 35mm projector to create a light pattern.

Heat is always a concern when you're running light through a GOBO so make sure you don't get it too close to your light source for a long period of time.

The term "gobo" is derived from "Go Between" or "Goes Before Optics" and is a physical template slotted inside, or placed in front of, a lighting source, used to control the shape of emitted light.