What's a Gobo?

I'm often asked this question when discussing lighting possibilities with a client. A gobo is a template of an image or words that is placed into a lighting fixture between the lamp and the lens.  Adjusting the lens will focus the image as it is projected onto a wall, the floor, or a backdrop. 
I needed a couple lekos for the musical South Pacific which were going to be outdoors for a few weeks. I chose this beat up old Altman leko. The gobo template holder is slid into a slot on the top of the light fixture.
There are many theatrical supply companies that create catalogs of stock gobos which they offer in printed catalogs or online. The three largest producers are Rosco, Apollo and GAM.  Typically, they're made from steel or glass, either laser cut or etched. 

Whatever areas allow light to pass through is what becomes projected. Moving light fixtures will often have several gobos which can be rotated and overlapped with each other.
I've used these stock gobos many times and they will eventually disintegrate under the intense heat from the lamp.  

Some companies use brass or a heavier gauge steel for longevity, but heat resistant coating on glass gobos also withstands the temperature.  This multi-colored glass gobo is made from bits of dichroic glass and should last a long time under normal circumstances.  I store my gobos in an old fishing tackle box with dividers.


The manufacturers will also create custom gobos from your design. A steel custom gobo will cost about $75+ before shipping. In a pinch I've had to create my own when there wasn't enough time or money to order the gobo. Sometimes I create the design and print several copies of it onto transparent film sold at office supply stores. I will then cut them out and overlay three of them and tape them together. This will work, BUT... the film cannot withstand the heat and it will begin to smoke and melt in the light. I found that in a standard Source Four leko, which uses a 575 watt lamp, I can raise the lamp intensity to about 30- 50%, depending on how much dark area is in the image which absorbs the heat, before it crumples up and smokes. This is NOT a safe thing to attempt if you don't know what you're doing. 

For South Pacific, I needed two gobos that would project, "Thanksgiving FOLLIES" onto a white parachute (see one of the stage photos in my last post). I hand-cut these with an exacto knife. Having the lettering look rough and hand-made was completely acceptable for the scene. I tried a number of materials but ended up using black wrap, which is basically heavy aluminum foil painted with heat resistant paint. They also make it with an adhesive backing, so I stuck one to the other to make it a little heavier and it was just the right thickness for cutting with the razor knife. I also used the black wrap to make what's called a "donut" or a "cookie" to place in the color slot at the end of the lens barrel. Cutting a smaller hole helps to sharpen the image being projected.
Feel free to file this post under cheesy theatrical tricks...