In the Sept - Oct 04 Practicing Oil Analysis magazine, there is a write up on doing a patch test for simple On-site analysis. I have been wanting to do this test at a Nuclear Plant for sometime now but have several hurdles to clear and looking for some help. I need something to replace Mineral Spirits that has a flash point greater then 140f and what microscope is the best for doing this test?

Lamp oil is an excelent diluent for reducing the viscosity of your lube oil to get it through the patch effectivly. I just checked a few MSDS sheets for lamp oil flashpoints and they run from 185-210 degrees F.

You need at least 100x magnification to get a good look at the particles. If you can get multiple lenses that can be usefull but 100x is where you will do most of your viewing. Look for a scope that has oblique lighting (above the patch off to one side). Most of the particles you will be looking at are opaque so bottom lighting will just show black where the particle is (looking at the dark side). If you have a light that shines down thru the lens you get too much glare from the residual oil/diluent unless you allow the patch to dry for awhile before viewing. You can also just use small lamp set beside your scope to illuminate the patch. Capability to mount or incorporation of a digital camera can also be usefull for documentation.

BuckHntr,
What is this Lamp oil, is it kerosene oil which is used in lamps and stoves? If it is that one, it will contain lot of contaminants and will give erroneous results.Generally for Patch test I dilute the 100 ml of test-oil with equal qty of Hexane (Of lab Quality 99.7% pure , but use it only after passing it through a 0.8 micron filter ), the mixture is now passed through a 0.8 micron membrane with the help of a vacuum pump. Yes, the Flash Point of Hexane is perhaps below 140 degree F, it is expensive also. If lamp oil can be used ,it will be economical too, but what about the solid contamination particles it will have ?

The Lamp oil I use is liquid parafin and is very clean. It is designed for liquid oil candles and to be smokeless when burned so it has been highly refined. As you do with your Hexane I pass the lamp oil thru 2 .8 micron filters before use. The particle counts I average for the lamp oil are 12/11/9 or so and my software automaticaly takes into account the particles in the lamp oil when calculating the count for the oil being tested.
Hexane has a flashpoint of around 7 degrees F (-22C) and I would not want to use something that volitile in my lab if there was an acceptable substitute.

Maybe a little bit late. One option to reduce contaminants from solvents or low viscosity oils is filter it before use it. If I am going to use a 5 micron patch, I filter the solvent through a 0.8 microns patch.