What Acid to Strip Chrome Plating from Plastic?

[nigelmercier]

I've brought the plastic inner frames from my Rutgerson Portlights home to strip the Hammerite I sprayed over the corroding chrome, then the chrome itself.

[Update]

Sodium Hydroxide solution (1kg dissolved in 10 litres of water) works very well to remove Hammerite, and doesn't appear to damage the plastic.

I had hoped that Hydrochloric Acid (35% dissolved in 10 parts water) would remove the chrome plating, but my test piece has been over an hour and I can't see any action.

Can anyone suggest a more aggressive acid to use?

 

[AntarcticPilot]

[Update]

Sodium Hydroxide solution (1kg dissolved in 10 litres of water) works very well to remove Hammerite, and doesn't appear to damage the plastic.

I had hoped that Hydrochloric Acid (35% dissolved in 10 parts water) would remove the chrome plating, but my test piece has been over an hour and I can't see any action.

Can anyone suggest a more aggressive acid to use?

It could be one of several things, and each would require a different approach;

1) It might be actual chrome plating. If it is, there will be a layer of copper under the Chrome. Chrome is very difficult to remove chemically; it forms a very resistant oxide layer that protects it from further reaction. Wikipedia suggests that treating it with a reducing agent followed by acid might work; Oxalic acid or phosphoric acid might work as a reducing agent.

2) It might be vapour deposited aluminium. however, I think that your sodium hydroxide would have removed it if that was the case.

3) It might be a paint; again I'd have expected the sodium hydroxide to remove it if that was the case.

 

[Lakesailor]

Google has loads of advice. This is one http://swiftysgarage.net/topic/6957265/1/

 

[Wooden Boat Fittings]

Traditionally,to remove chrome plating from a bronze fitting you'd take it to an electroplaters and get him to apply the reverse chemical process to the one that put the coating on in the first place. But whether that would work with a plastic substrate I'm afraid I have no idea. It would probably be worth asking though.

Mike

 

[nigelmercier]

So far I have tried:

Hydrochloric Acid: some discolouration only
Strong household bleach: nada
Phosphoric Acid: zilch
Strong Ammonia: watering eyes
Sulphuric Acid (a few drops stolen from a battery): TBA

 

[vyv_cox]

Sodium hydroxide should do it. Not clear from your first post whether you have tried it.

 

[Tranona]

Having had similar problems with mine I have painted them matt black. Look great and very easy to touch up if necessary.

 

[nigelmercier]

Sodium hydroxide should do it. Not clear from your first post whether you have tried it.

Yes, this is what I used to remove the Hammerite.

 

[VicS]

Yes, this is what I used to remove the Hammerite.

According to the text books chromium dissolves slowly in dilute sulphuric and hydrochloric acids/ but I guess not when protected by an oxide film,

No details but apparently the oxide film can be destroyed by touching the chromium under the acid surface with zinc. Maybe an idea to experiment with if you have a bit of an old anode. Maybe aluminium would do the same??

 

[nigelmercier]

Latest trial is with Calcium Hypochlorite, there is a lot of foam and black scum on the surface, so something is happening.

 

[rob2]

If your luck's like mine that means it's dissolving the plastic and you'll end up with a perfect chrome cast of the item! ;-)

Rob.

 

[Wooden Boat Fittings]

... apparently the oxide film can be destroyed by touching the chromium under the acid surface with zinc.

As I said, talk to the electroplaters....

Mike

 

[nigelmercier]

Latest trial is with Calcium Hypochlorite, there is a lot of foam and black scum on the surface, so something is happening.

No change, just a load of globules on the surface, looks like smallpox.

Currently trying again with 18% HCl (36% Hydrochloric Acid dissolved 1:1), this is about the most concentrated you can get without it fuming. Some initial fizzing, but that was probably Hypochlorite residue. The only change after an hour is that the areas which had green corrosion have gone copper coloured.

Vic, when you say "apparently the oxide film can be destroyed by touching the chromium under the acid surface with zinc..." do you mean literally touching it, and all electrically connected parts will clear?

 

[VicS]

Vic, when you say "apparently the oxide film can be destroyed by touching the chromium under the acid surface with zinc..." do you mean literally touching it, and all electrically connected parts will clear?

You know as much as I do I am afraid.

 

[macd]

According to this: http://www.cromoplasticacmc.it/Sito_ENG/Manufacturing_process.html
the plating is palladium, nickel, copper, nickel, chrome, so perhaps unlikely that any single chemical would remove all.

 

[Steve Clayton]

Try Lysergic

For a while you won't care about the chrome plating

 

[121]

Aqua regia? (1 part nitric to 3 parts hydrochloric - both concentrated).

Hugely unpleasant stuff...

 

[nigelmercier]

Aqua regia? ...

I was wondering about this, but in a dilute form. Currently testing 1 litre of 18% HCl plus 200g Oxalic Acid crystals, but I don't think it's doing much:

 

[cliveshelton]

Aqua regia? (1 part nitric to 3 parts hydrochloric - both concentrated).

Hugely unpleasant stuff...

Dont mess with this stuff unless you have the necessary experience, gloves, goggles, fume extraction etc. it eats everything , especially organic matter (including flesh and lung tissues). If you do, dispose of carefully. Gets hot when diluted like many conc. acids). Also it might form nasty things with some chromium compounds. But you won't care 'cos you flesh will be dropping off anyway.

I doubt if it will work though to your satisfaction. I would use mechanical means to get back to the substrate you need. Quicker in the long run than experimentation.

 

[nigelmercier]

Dont mess with this stuff [Aqua Regis, NHA] unless you have the necessary experience, gloves, goggles, fume extraction etc...

I'm pretty sure we used this stuff at school for cleaning the glassware, although it could have been Chromic Acid!