I think the point he's making (which was my experience too when I last used a lead bag - decades ago), Newt, is that if the screener sees a "black blob" they will not assume that it is film and therefore OK... they will assume that they cannot assess the situation and either re-scan in hopes of a "better angle" or pull the bag out for hand check. That hand check may be performed primarily to figure out what is being concealed more than to be nice to the guy carrying film. When that has happened to me, the entire contents of my carryon have been examined rather than just the "black blob". You appear to have had better success with your lead bag than have others.