Citric acid is a good tip!

My pickle juice is a mellow blend of nitric and sulphuric acid, with a dash of hydroflouric acid in a convenient paste format with an indicator to let you know when you've neutralized it. It was pretty pricey too; ~$80 for a big bottle of it. If you do get into welding stainless a lot, and wish to use something like that, do read the MSDS and order a tube of Calgonate for your emergency kit. Many off the shelf stainless steel brighteners have similar formulations. But I digress...