Salfumant

I was given this stuff to clean the rust off some old decorations. As you can see it comes in a fairy liquid type bottle. I was told it was "strong stuff" and I did try to read the print on the bottle but a mixture of blurred print and poor eyesight meant that I couldn't. I do know there were none of those European "danger symbols" except for the cross that means irritant. There was no mention of it being corrosive. It was bought across the counter at the local ironmongers and it has a picture of a lavatory on the side to suggest that it can be used as a toilet cleaner.

In fact it is Hydrochloric Acid.