Best technique for a 50/50 black?

[hawgdriver]

I've been experimenting with different masks and techniques to get a laser-straight 50/50 black dye to work. So far, as dyeing medium I've used top-painted shaving cream mixed with Rit graphite synthetic, or just the Rit/water/acetone in a pan. To mask the disc I've used different types of tape (electrical, duct, blue masking).

Sometimes I've let it sit at room temp, but the strongest/quickest results have been using small oven to accelerate the process under something like ~150° F (I have to briefly cycle the bake function and let it sit).

Anyways, my end goal is to make a half orange half black disc with no bleeding. The only precise results I've achieved are with the electrical tape, but not if it overlaps any other tape.

I was going to try contact paper next. Just looking for any hints, thanks!

 

[seedlings]

I have done electrical tape and contact paper with lotion based dye. If I take plain lotion and hit the edges, then wipe off, then it's the plain, colorless lotion that seeps in, leaving a crisp line. So, if I were trying what you say, I'd put a strip of electrical tape with one edge down the middle, run lotion down that edge, wipe off, then use color (I like to put the disc in a container, with clearish lid, outside in the sun) until set. For the next color, get your tape on that same exact line, plain lotion, wipe, then 2nd color. If you're using a different method, perhaps you can adapt, like hit the edge with plain shaving cream instead of lotion?