Before you spend a lot of time trying to make something work in a way for which it wasn't' designed, take a look at Ebay. There are good densitometers available at low prices, now that the places that paid big bucks for them when they were new don't need them anymore. Don't buy the Kodak Model 1, though; that requires that you visually match the shade of a doughnut with that of the hole, and is no fun at all. Get something with a meter.
Jim