If you want some interesting information on Perceptol, read Barry Thorntons "Edge of Darkness". It's a wonderful book on how to get the sharpest prints you can, and covers everything from cameras to tripods to lenses to enlargers to...developers. Although Mr. Thornton went on to develop his own specialized developers and then started into digital before his untimely death, he has a lot of good to say about Perceptol. One quick read of the book will sell you on Perceptol as a "sharpness" developer that was once widely available and should once again be available very soon.