Toying around with some steel trying to make it rust quickly. Well, I failed, because it turned pretty much completely and smoothly black. I didn't degrease it first, and I guess that is why a few splotches didn't turn black.

I first left the steel in citric acid overnight, and nothing happened. Then I left it there for a couple of weeks, and still nothing happened, and I forgot about it. Then some of the water evaporated and the steel was exposed to air.

When I remembered to check it, brown rust had formed on the air-exposed steel. I submerged the steel again and still nothing happened. I then threw away the citric acid and filled the container with snow to remove the acid stains and put the steel in the snow.

That was a few days ago, and today the steel was black.

The blackened steel actually looks very nice and could be cool for my current project, but even if I knew how to repeat this I have no way to treat 125cm X 80 cm sheets.