what gel are you using? brand? price? link?
these have always been some of my favorite types of shots, but i ain't spending 80 bazillion dollars on a square piece of glass from Lee (don't care how good it is).
You could go to harbor freight or some other cheap tool shop ang get a number 14 welders glass. I was serious when i suggested that may be what was used here. It is dark enough to allow you to look at the sun, like solar film. Tbe 14, i believe,is the numberof halves, or stops, of light it cuts out. Probablyhave to deal with some color cast, and use some gallers tape to hold it to the lens, but it should work.
Metalized solar filters are also available in sizes thatcan be mounted to lenses, for usually around $90. They definitely haveacolor cast.