How do I tint (slightly black) a clear dura-lar polyester film sheet with an even color coating?

Background: I'm working on a final for art school, and I wanted to find a material that is pretty much exactly like the Dura-Lar .005 clear film (archival polyester film) I bought from Blick, but I wanted it to be slightly tinted gray, and still transparent enough so that I could layer the sheets a few times to change the intervals of opacity. I couldn't find anything like that at Blick or online, so I gave up and settled on the Dura-Lar.

Present: I'm currently trying to tint the polyester film manually by using Piñata Alcohol Ink mixed with Piñata Alcohol Ink Claro Extender, and 91% isopropyl alcohol, as a more affordable substitute to make mistakes with.

Problem: I want to apply an even coating of the diluted color to make the sheet a slightly darker color, but I'm having trouble applying the ink with a consistent, even coat. Everything I've tried has resulted in visible brushstrokes or texture in the color. I want it do be as even and consistent in color/transparency as posible.

I've tried using a brush (sponge and bristle), pouring the mixture directly onto the sheet, and nothing has been quite consistent/smooth enough to my liking. Is there something I'm not thinking about? Do I have the right idea with alcohol ink? Honestly, anything would help. I have been taking adderall left and right, not sleeping, and don't think my brain is working properly, but I can't afford to take a break. Please help a struggling artstudent :')