Clean all parts and dry with acetone. In a polypropylene (recycling number 5) tub, dissolve 110g of selenium dioxide in a liter of distilled water, connect the positive terminal of a 9-volt battery to the part you're trying to blue, connect the negative terminal to a piece of coat hanger wrapped in cotton balls. Add a splash of hydrogen peroxide. If you want a really rich finish on your part you're going to want to take it out and polish it intermittently because this blue will form very quickly.
If you can't find selenium dioxide, smash up some selenium capacitors from scrap electronics, sift, and dissolve them in strong nitric acid. Copper contamination is not a problem but do not get lead or tin in there.