Sorry to drag up an old thread but just wanted to add that I used Harpic Max 10 this last weekend to remove the mill scale off some ground anchors I'd made before painting them.
It has 9% hydrochloric acid in a gel format that I worked in with a scotchbrite pad to take the scale off pretty quickly.
£1 a bottle at Asda at the moment.
I didnt! It was a bed I made, and i left the millscale and welds and grinder marks as-is.
If I was going to paint it I would have gone for a Sparkle EFX purple colour, but the guy would not ship it from the states. I thought that was dumb of him, but free will and all, what can you do.
Here is a section of the bed, its quite tall, 4 feet, so i made railings to stop me falling out and bouncing my head while drunk, it happened twice. I like the gunmetal colour. In fact I love it.
So in the end I just cleaned it a few times with thinners and a rag and left it. Its been like that for about a year now with no rust at all that I can see.
I really do think there should be a transparent coating for metal that will stop rust. I'm not the only person I've come across that likes the look of raw steel.