Hi Dave, I have been using Citric acid as pickling solution for some time now, and it works as well as sulphuric acid, but avoids the burn holes in trousers & overalls.
I mix about a heaped table spoon in about 1 gallon of water, and add a little more as the solution ages with use.
Like all chemical processes, it works quicker if warmer, so putting parts in whilst warm speeds things up.
Citric Acid is quite safe to use, but should be washed off with copious ammounts of water if splashed in the eye, or other sensitive areas. I know we can drink it, but it becomes a good poison with copper salts disolved in it!
The home brew shop is the cheapest source of supply, much better than the little pots that chemists sell.
regards
Brian