Yes Jazz - I know all this and more (chemistry at Uni), thats why I recommended the Wickes stuff. It will get the zinc off in about 15 to 20 minutes and is not as dangerous as more concentrated hydrochloric or sulphuric acid. I am not so sure about chip shop vinegar, acetic anhydride would do the job, but I certainly wouldn't want to inhale the vapours of that stuff.
I have been told that in Barnsley, the pigeons fly backwards to avoid getting the shit in their eyes. Is this true Dean ?

Happy Holiday.

Rob