In reply to Steve Wolstenholme ) who wrote this
in , I, Marvo, say :

On Mon, 6 Aug 2007 14:44:20 +0100, "Barb"
wrote:

Hi, I've got some horrendous rust stains on flagstones, from old
cast iron pation furniture.


The rust stains will have penetrated the flags down to quite a depth.
You will need to clean to the same depth. Try neat chlorine bleach and
leave it for a few days.

That's what I meant about largely unsafe :-)

Another "cure" is conc hydrochloric acid or fuming nitric. It will damage
the flags, as will the bleach, I suspect.