In the first National Treasure movie, what invisible ink stuff did Ben use to get Abigail's fingerprints?

Question

When Ben made that green liquid stuff and covered the button he gave Abigail in it, which gave him her fingerprints, what did he make the stuff with? What was the recipe?

Answer 1

I bet it was diluted highlighter ink, because its not visible when diluted and glows when exposed to black light like he did in the movie