Elmer's Glue -> Modeling Clay?

I've been looking into cheap alternatives for clear casting resin, and came across a simple, kid's recipe for modeling clay that involves equal parts Elmer's Glue-All, cornstarch and flour. What I'm wondering is - does this stuff dry translucent? I would like to either cast a 'brick' or 'shell' (depending on how thin it has to be to be translucent, if that applies) that will diffuse the light from 7-8 LED's to make an even color (the LED's are evenly spaced).

In addition, if I do have to cast a three-dimensional shape out of this, would it be possible to coat the sides with petroleum jelly for a 'mold release'? As far as I know, it should work - an often-used trick for glue bottles is to coat the bottle caps with mineral oil or Vaseline so they don't stick.