On Fri, 29 Aug 2014 08:18:06 -0700, wrote:

On Fri, 29 Aug 2014 07:16:08 -0700, RobertMacy
wrote:

On Thu, 28 Aug 2014 18:19:39 -0700, wrote:

...snip...

I still have some red chalk lines that have survived dozens of
pressure cleaning and 2 hurricanes. Red is pretty permanent.

They had to use that carcinogenic red food coloring somewhere!

Seriously, the "red" seems to come from iron oxide according to the
MSDS so barkeepers friend, naval jelly or some other rust remover
might work.

maybe "Whink", a commerically available mild hyrdofluoric acid for
removing rust stains

but wear gloves!!!