I think bobscoggins got it. In about 1975 a local painter had a chopped knuck that had that stuff on it. I asked and he said it was applied electrically somehow. Looked like shit down low from engine oil. Tank was cool tho. Was back there about 10 years ago to try and buy the knuckle. The painter guy sold it the week previously. To walrus head (the old man Teutel from OCC) SHIT