Haven't heard of Bentone before, Matthew. I've never used real Petrobond -- too expensive for my tiny hobby budget, both in original cost and for shipping, since it is heavy. Also, the idea of handling and breathing burnt fumes of some secret commercial oil formulation wasn't as appealing as just working with plain water and steam.
But I am curious about it. I've watched at least one video about someone "making petrobond". It turned out that he was using sanded tile grout mixed with motor oil -- 25 lbs of the grout and a quart of the oil. The video didn't inspire me to go out and try it, and it didn't seem convincing that the sand he'd come up with was the equivalent to Petrobond. I guess partly because he seemed so odd in his casting practice anyway. Also, modern sanded grout has some odd organic additives. But again it was of interest. And, who knows, maybe his results were equivalent, and the health effects not pressing. The camera work wasn't good enough to really read the casting finish quality.
My understanding about Petrobond is that casting finish for aluminum is greatly improved by it -- that's its main advantage. Also that it isn't applicable for iron, but I may be wrong in that.
I think little on the internet has been devoted to improving finish for aluminum casting using conventional water/clay based greensand. But actually there is a fair amount you can do. I think using a facing sand is important, as is moisture control, and understanding local ramming pressure to yield a high quality result.
I would like to try Petrobond to see for myself if there is an advantage in finish, compared to what I'm used to and to what degree it's improved. But as I said, it's not in my tiny budget for shop work.
