How can you tell if oil is removed from the surface?

Question

I'm doing a project relating to dish degtergent and so on. Though finding whether the oil/grease is removed from the surface is crucial. My science teacher says there is a way to tell, but is not sure, and she has approved of my project. Pleases give a way based on facts or other reliable sources. Do not give assumptions done by visuals and etc. No, I don't have all the science tech in the world, so try to keep it simple without using a bunch of science lab tools that an average person might not have. Please and thank you!

I am testing on either metal or ceramic surfaces

Answer 1

There is something called a "water-break-free" test used on metal surfaces. You run water over the surface. If it smoothly covers the surface, it is clean. If it breaks up at all, then there is oily contamination. Oils are hydrophobic, so that's why the water breaks if there is contamination. If you use this test, I'd suggest starting with a super clean surface, hold it under running water, and then pull it out to see what the water does. Then rub a little oil on it, repeat the test, and see the difference. It takes a bit of practice to get good at seeing the water breaks. Note this will only work on surfaces that are hydrophilic when clean - like sheet metal. You may need to go to a metal machine shop and buy some aluminum test panels for your project.

Answer 2

My father, an environmental scientist used to test for the presence of oil in his oil pollution research cases and he said a simple test is to use plain paper and dip it in the sample.
A presence of oil will turn the paper translucent. Good luck.

Answer 3

Hi. Tape will not stick to an oily surface.