Watching this video that I posted recently, I always thought that plating shops reverse chromed parts in the chroming bath to remove the chrome & nickel layers of plating, in order to minimise any damage to the substrate steel. Problem is Chromic acid is really nasty stuff, hard to get hold of and I don't want to be 'Ashimoto of East Yorkshire' with the local Erin Brockovitch on my back.
However, in the video posting and linked again here, the pro company used sulphuric acid with a couple of 'additives' to reverse plate strip the chrome and nickel from steel parts.
https://www.youtube.com/watch?v=RU9l66_XmDkI have a few little bits off my C110 50cc Sports to re-chrome and I need them doing ASAP and can't afford to wait the lead time at Prestige. The other thing is that I need repairs doing to a few parts with silver solder and bronze brazing which means getting the parts stripped, repaired and then back to the chromers so I put together a small setup to have a go myself.
Research on the internet recommends 5% glycerine added to a 50% strength sulphuric acid, the glycerine evidently limits the damage to the steel base metal. Battery acid is weaker than this so I got some One-Shot drain cleaner I have had in my garage for about 10 years. I remember buying it from a plumbing place in Hull and when I asked for it , the smart ar$e behind the counter says " Do you know who John George Haig' was?" .. so me being the equivalent smart Ar$e replied " Yea he was the Acid Bath murderer in Crawley.' ...So he then plonks the bottle of drain cleaner on the counter and says " Well this stuff is 3 times stronger that the stuff he used''.. " sign here " .. presenting me with some kind of poisons register.
Anyway, the safety data sheet for the drain cleaner (made in good old 'ull by the way Orcadian) states 91% concentrate sulphuric acid, so I mixed the 1 litre bottle with 910 mls of de-ionised water .. Acid to water NOT water to acid, as it was drummed into me as a schoolboy. It exotherms (heats up) quite a bit so the usually PPE bol*cks applies.... mask , rubber gloves, old clothes blah blah.
I set up a little bath and did everything outside and used a car battery and rheostat (variable resistor) to provide the current and some lead sheet from my dodgy mate, as the cathode (negative terminal of battery). The anode (positive terminal of battery) is the chrome part to be stripped ... the rheostat is used in series with the positive terminal to control the current. I reckon you could use combinations of headlamp bulbs to limit the current if you don't have a rheostat.
I started out being all fancy with a multimeter etc. but they only usually measure up to 10A DC, at best, so I just adjusted the current until there was loads of fizzing at the electrodes.
I must say it works really well and no real hassle to the base steel as long as you keep your eye on it and don't leave it in the bath any longer than required.
On triple plated parts you are left with the copper layer, so it is obvious that all of the nickel has been stripped off.
What I do with the non-triple plated parts is to paint the part after stripping, with acid-copper marking solution that the old boys used to use for marking out steel parts. You basically get some copper sulphate dissolved in de-ionised water and add a few drops of sulphuric acid to it. As soon as you paint the de-plated part with the solution it turns a lovely salmon pink and any areas not stripped you will see a different colour patch. The copper plate doesn't really bond to the mild steel so it easily buffed off afterwards. Proper copper plating is done with cyanide to get the initial copper layer and is very hard to remove without using nasty chemicals.
If you look at the rear shock cover in the 2nd photo, this wasn't triple plated but after stripping it was brushed with the copper marking solution and you can clearly see that where the top part was not fully immersed in the bath and hence is still silver, not salmon pink.
My bath is only small but my mate is going to donate me 5l of conc. sulphuric acid, in order to make up a bigger 10 litre bath .. plus more lead from my dodgy mate of course ! Sorry , it wasn't me vicar
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