I'm planning to do a blotter test, too. ..and have a few "?"s: 1) How long should I wait to take the pic after blotting? 1a) How much oil (how many drops) should I put on the media? 2) If I don't have a white business card, what's the next best paper? --Can I use real white filter paper from the chemistry lab? --Do the printed stuff on the back of a buisness card matter? --What kind of paper should be avoided? 3) How "good" are the blotter tests? I mean: Can I really base the oil-life left on the results? Thanks a lot.