The picture below is of four mono prints done with thickened dye. I had the dye in squeeze bottles and squirted it on and used various tools to smear the dye around.
For pieces bigger than my glass piece, I use vinyl. I bought several yards at JoAnn's and I keep it rolled on a cardboard tube.
There are several other ways of doing mono prints, but this is my favorite way. There's no right or wrong way of doing it - just do what works for you.
On another note; my other blogwas nominated for an award today. So I had to nominate three other blogs for the same honor, so go check it out.