Parts Identification Methods

Maybe this?

Yes, spray paint sounds like a good idea (I'm not the OP, and I don't know all the constraints).

Possibly RFID tags would be worth considering, also. (They can be fairly inexpensive, and could identify the exact type of part.) Again, I'm not the OP, I have no idea of what is driving this desire, nor the value of a solution (how much money is worth spending).

Sharpie!

Forney paint markers.

Glyptal 1201

It might be cheaper to give up and replace them. Trying to get tools to make a round trip seems to be a violation of one of the fundamental laws of physics.

Don't know what exactly you are doing, but if this is meant to be temporary, go get some bumper sticker stock in a particular color to identify your section of the plant and cut it into little squares. You would have to do an initial cleaning to stick it on the parts, (quick wipe with alcohol or acetone), but once stuck on, the adhesive is pretty tough. If you need to remove them later, use a hair dryer to soften up adhesive and remove.

Not sure what type of parts it is that you are trying to keep identified....but I know that our company has actually applied fluoropolymer coatings of different colors (orange, blue, green, yellow, etc...) to tools which go on oil well rigs. Tools are color coded differently for each level on the rig making it real obvious which tool came from what level. The fluoropolymer coatings are resistant to oils, solvents, etc...no problem. Thickness of the coating is very thin(Typically less than 1.0 mil thick) therefore no problems in fits, etc....The company is located in Houston, Texas and is called Southwest Impreglon Inc. You can do a google search.