i'll occasionally use a zinc plated stock. if its square, i take a flap disc to it on all sides. if its round stock i either flap disc or put a heavy twisted wire wheel to it on the grinder.
After either prep, ill toss the shorter pieces into the fire pit in the back yard (as long as theres no wind) and cook off anything that I may have missed prior to forge heating the stock. I had a run in with fume fever, and I'll avoid plated stock 99% of the time. if you really must use plated stock, get the plating off as best as you can. Daswulf's muriatic acid bath is a good idea also, Ive done that also, but try to do that outdoors in fresh air to avoid fumes from that process.