Kim,
Are you talking of Millipore Patch test with Hexane, 47 mm dia membrane of 0.8 micron porosity and a vacuum pump.Oil is first diluted with the help of Hexane, then it is passed through a 0.8 micron membrane, oil passes but the solid insolubles remain on the top of membrane forming a white grey or black patch which can be viewed with a 100 X microscope or compared with a Coloured Patch chart to reveal the condition of oil. It is a very reliable test, sometimes better than Particle Counter and is always much much more economical than Particle Counter. If it is so, i have that Patch chart. write to me at pa_ranchi@yahoo.com