hi, I'm sure the ammonium nitrate will work it just seems to have a lesser amount of nitrogen, just as long as it has no other ingredients and kind of looks like small clearish white granules. I tried a few things before i could get the urea but nothing worked well if at all.
As for paint i use standard solvent based auto paint, mixed and sprayed through a gun and spray [rattle] cans of celly or acrylic. It will take a lot of spray can clear in many coats to build enough to cover the tactlie finish of the crystal efect.
I wouldn't use water based paints for the contrast coat [usually the black coat] as it will most likely wash off with the crystal stuff.