heat treated

Volcanic Stainless Steel

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Is anyone familiar with this technique of coloring stainless steel with heat? An Oregon artist named Milo uses a liquid he doesn't identify to "paint" images on 300 series mill finished stainless steel sheet. He then uses a torch to burn the images onto the sheet and claims the resulting color and image are permanent. I'm curious what chemicals he could be using. There is a video on his website where you can watch the process. One of the chemicals appears to be similar to a petroleum jelly and the other is a liquid that is sprayed on the image.