I don't know - it was redish in color, and I believe water based. When I set out to do this I picked up the yellow pages and the first jewelry repair person I talked to had an interest in the subject - because he had recently used his ultrasonic jewelry cleaner to clean the injectors on his Saab, apparently very successfully. I figured I had nothing to lose, took the sensor out of the housing, removed the rubber o-ring and gave it to him. He refused payment, saying "I didn't do nothing" - meaning he just lowered it into this "bath" and took it out 30 minutes later. I'll see if I can find out what it was.