I promise that this is my last epistle about electrolytic derusting. It's just that I never could find out how much better Washing Soda is than Baking Soda as the electrolyte for this process. So I ran a controlled test and here are the results:
I was told that after soaking steel in vinegar to remove scale/rust it was good to use a baking soda and water solution to neutralize the acid. But when I went to the store to buy some baking soda, I found there was both washing soda (with the detergents) and baking soda (with the baking supplies) both made by the old standard Arm and Hammer. Reading the box, I couldn't find anything to tell me if they were the same or different - and at that point, I wasn't sure which I was told to use! I never realized there where two types of Arm and Hammer soda.
But your page has now improved my education a bit on those two. My guess, is that either would work, but that that the washing soda would neutralize more acid per pound and that baking soda would be safer and milder to work with. At least I now know there is a real difference between the two now.
However, doing some test, I really couldn't see any difference between rinsing the piece in the baking soda solution vs just rinsing it with water (or soap and water). Do you ever descale with vinegar? And do you rinse the finished piece in anything other than water?
And does anyone know if baking soda or washing soda has any other interesting uses in blacksmithing I should know about? :)
ABOUT DESCALING, NOT DERUSTING: I have a friend who uses vinegar to descale most of the time. It takes a long time to descale that way compared to other chemicals that I use.
Personally, I use much harsher chemical for descaling. Muriatic acid that is available at hardware stores works well. An even stronger form of the same (I think) acid is "The Works" toiler bowl cleaner. Use either at your peril. Get serious about good ventilation. Even a few wiffs of the stuff may give you a nosebleed. By the way, toilet bowl cleaners that work on the basic side of the ph scale don't work for this application, as far as I know.
To those who may be wondering, descaling and derusting are different processes. Strong enough acids will do both, but they eat into the iron itself during the process. The electrolytic derusting processs, which is the topic of this original post will NOT remove scale!!! Only red rust...
Regarding neutralizing after acid descaling: I'm not surprised that the soap and water gives about the same results. As long as you get all the acid off the part, it will probably be neutral anyway. However, the part will rust again quickly if you don't protect it, won't it?
I have large plastic tanks that contain HCL (swimming pool acid) and the other contains a bag (10#'s ) or two of Baking Soda.
I de-scale and then neutralize. When the soda that is on the bottom of the tank starts to disappear, I add more. I want a well anti-acid bath ready if I get a hand into acid or just my work. Welds a bit better without scale.
Thanks for the great posting. I built the rig using one of those 5 gallon white plastic paint buckets and 6 rebars, including two that were cut long and bent into an "L" to cross the bottom. I couldn't find the Washing Soda so I used the baking soda and hooked up the whole rig to an old auto battery charger I had. It's almost like magic. Depending on how much amperage I turn on, the fizzing is quite noticable. The parts come out just like your pictures, black and pitted, but no red rust remaining.
Since gun blueing is actually an oxidized finish, would this technique work to deblue a gun prior to rebluing? Or is gun "blue" the wrong kind of oxidation? I don't have any that I want to risk on experimentation at this time and wondered if any of you have tried it.
Sorry for the late reply. No, I haven't tried that. And I don't know what the various blueing methods really do. Might get some help from the Brownell's Gunsmith Kinks books, tho. They are fun to read anyway.
It wouldn't hurt to contact Brownell's and simply ask them.