After many years and a whole lot of trial and error and research I have found a method of rust blackening that works very well for me. I did not invent it and it does not belong to me. As already stated it is a variation of techniques that have been for some time to achieve a decorative rust patination. My contribution to this process is to be able to do it in a matter of minutes. It is durable, attractive and *black* and it takes me about 30 minutes to do. It goes like this;
Don't panic about the pits on these fittings...they were patinated after a few botched attempts at this. Is does not take days to rust the fittings and you don't need urine or bleach or all that. This flash rust routine is much quicker.
Starting with clean steel (degrease and clean with alcohol) and handle with clean hands or vinyl gloves to keep oil from contaminating the surface. Make a simple solution of hydrogen peroxide (the stuff they sell at the drug store for 99 cents), table salt, and vinegar. Put about 4 ounces of peroxide in a glass jar and microwave it until it is hot but not boiling. Add salt and stir and then reheat. Continue heating and adding salt until the solution is saturated....you can tell because the salt stops dissolving and starts to accumulate at the bottom of the glass jar. When saturated add about an ounce of vinegar (what kind does not matter) and pour the solution into a spray bottle. I use empty and very clean butter spray bottles.
Take the steel fitting (clean, remember?) and run it under hot tap water till it's hot. Remove it, and then spray it liberally with the hot solution. It will steam, fizz, foam and drip so don't do this over the living room carpet or your wife's clean bedspread. You will see red rust appear immediately and as the foam dies down spray it again and again. After a few spray cycles rinse it under hot tap water, brush it with a soft toothbrush (not *your* toothbrush...use someone else's) and then run it under hot tap water again. And then repeat the spray and foam routine until it is literally covered with a thick coating of red rust. Maybe about 10 cycles and maybe it takes about 12 to 15 minutes.
Then place the fitting into a pan, fill it with water, and set it on the stove. Heat until the water boils and then boil it about 10 or 15 minutes (I use distilled water) or until the fitting is black. Pull it out of the water (use your fingers! If you don't get burned it ruins the whole thing) and while it's still warm rub it with mineral oil or Renaissance wax. The wax will make it shiny...the oil will evaporate and leave a cool, dull black antique look.
It's done. Rub it with a soft cloth to remove any loose rust. This procedure will rust without pitting and the surface will be slightly matte looking. And I was just kidding about the burnt finger part. Use a stick or someone else's finger.
Good luck.
Brian