Hi.
Thanks for your reply. The workpiece I have is a die-cast zinc-alloy (95% zinc). When I apply the acid stripper, It phosphatest he surface to a dull grey. I then vigorously remove the phosphating by scrubbing with coarse steel wool back to bright zinc. Here is the MSDS for the stripper that I am using.
http://www.birchwoodcasey.com/sport/.../16125-BR1.pdf
I cannot use sulphuric alone as it unfortunately isn't available here in the UK.