07-05-2012, 07:51 AM
Shuffling through my notes, I've unearthed some info on cleaning tarnished items by electrolysis. I can't recall the source, and I haven't tried it myself, so I can't make any claims as to the effectiveness. It reminds me of science lessons long ago when the science teacher illustrated the process by cleaning tarnished pennies. (I don't tihnk I was paying attention at the time!). For what it's worth, here are the notes on the process:
Often it’s necessary to clean heavily tarnished items when renovating old radios and electronic items such as connectors. But abrasives can be too harsh and impractical for many items, especially if they’re plated or can’t be dismantled.
The use of acids is too harsh, and would, for example, strip the silver plate off the pins connectors - likewise mechanical removal of tarnish and damaged plating would leave a ruined connector.
Someone had gained experience in de-rusting chassis by electrolysis, which had worked well.
What you need to do this is:
Plastic container (large enough to hold the items and allow a covering of fluid)
A source of DC current 10-30v @ 2amps with a series Ammeter to monitor the current being drawn.
A suitable electrode for the positive side of the supply (a brass block is OK, but stainless is better)
Connecting wire
Salt
Water
The Method:
Attach a wire to the item you wish to strip (or clean), suspend the item in the plastic container (it must dangle in free space) Connect this to the NEGATIVE terminal of the supply.
Attach your other electrode to the wire and POSITIVE side of the supply, then drop the electrode into the container.
Make up a solution of salty water - the stronger the solution, the higher the initial current flow....
Fill your container so that the item to be cleaned is fully immersed.
Switch on supply and note current flow (you should see some bubbling around the item you wish to clean - if not then the supply is connected incorrectly!)
For heavy cleaning/ stripping then the full 2 amps will do the job, for a light clean then keep the current low, and inspect frequently.
Final Cleaning
if you have gone for the real heavy clean then brass will come out a little discoloured - just give it a good scrub with a Brillo pad to remove this. You will end up with a tub of fairly grotty mess - this is mainly a mixture of copper sulphate, which can be disposed of by diluting with plenty of water.
It may be that common salt (sodium chloride) is perhaps not the best idea for a number of reasons. Some other salt (in the chemical sense of the word) may be better if available. Washing soda might be better, although it will attack aluminium and zinc.
The reasons to avoid common salt are:
a) Chloride ions play a powerful role in the rusting process. Having got your nice result they lurk until the humidity gets high and then the rust may break out again much worse.
b) Any remaining sodium chloride is hygroscopic (it will attract water) and thus will provide the wet conditions necessary to start up the rusting again.
c) A slight risk that you may discharge chlorine gas at your other electrode, but more likely hydrogen, but in any event, at the size of operation we are using here, the quantities are negligible. You do have to rinse the object thoroughly after the process is carried out, but it’s debatable whether the very dilute salt solution needed would be a corrosion issue - around 5g in 1000ml. (The salt is only there to make the water conduct electricity a little better).
A carbon rod might be a better electrode, e.g. from an old-style U2 battery, (do they still have rods down the centre I wonder?). Maybe a carbon arc welding electrode would be an alternative, though they’re usually copper plated. The other electrode does dissolve to a point (hence the comment regarding stainless). However, it shouldn’t migrate to the item being cleaned, as that is repelling.
If you have used salt it maybe a good idea if you boil the object in distilled water, (or water from a filter jug) or if it won't stand boiling, then soak in cooled boiled distilled water, to help remove as much of the salt from pores in the surface of the item.
If there are concerns about the salt, as weak solution of sodium carbonate (washing soda) or a weak acid like lemon juice or vinegar might be good alternatives - the two latter will also brighten brass after electrolysis as well. To really brighten brass, clock cleaner (detergent + ammonia + oleic acid) does an excellent job.
Hope that's of interest - maybe those with an enquiring who wish to clean any tarnished brass items mind might wish to give it a go?
Often it’s necessary to clean heavily tarnished items when renovating old radios and electronic items such as connectors. But abrasives can be too harsh and impractical for many items, especially if they’re plated or can’t be dismantled.
The use of acids is too harsh, and would, for example, strip the silver plate off the pins connectors - likewise mechanical removal of tarnish and damaged plating would leave a ruined connector.
Someone had gained experience in de-rusting chassis by electrolysis, which had worked well.
What you need to do this is:
Plastic container (large enough to hold the items and allow a covering of fluid)
A source of DC current 10-30v @ 2amps with a series Ammeter to monitor the current being drawn.
A suitable electrode for the positive side of the supply (a brass block is OK, but stainless is better)
Connecting wire
Salt
Water
The Method:
Attach a wire to the item you wish to strip (or clean), suspend the item in the plastic container (it must dangle in free space) Connect this to the NEGATIVE terminal of the supply.
Attach your other electrode to the wire and POSITIVE side of the supply, then drop the electrode into the container.
Make up a solution of salty water - the stronger the solution, the higher the initial current flow....
Fill your container so that the item to be cleaned is fully immersed.
Switch on supply and note current flow (you should see some bubbling around the item you wish to clean - if not then the supply is connected incorrectly!)
For heavy cleaning/ stripping then the full 2 amps will do the job, for a light clean then keep the current low, and inspect frequently.
Final Cleaning
if you have gone for the real heavy clean then brass will come out a little discoloured - just give it a good scrub with a Brillo pad to remove this. You will end up with a tub of fairly grotty mess - this is mainly a mixture of copper sulphate, which can be disposed of by diluting with plenty of water.
It may be that common salt (sodium chloride) is perhaps not the best idea for a number of reasons. Some other salt (in the chemical sense of the word) may be better if available. Washing soda might be better, although it will attack aluminium and zinc.
The reasons to avoid common salt are:
a) Chloride ions play a powerful role in the rusting process. Having got your nice result they lurk until the humidity gets high and then the rust may break out again much worse.
b) Any remaining sodium chloride is hygroscopic (it will attract water) and thus will provide the wet conditions necessary to start up the rusting again.
c) A slight risk that you may discharge chlorine gas at your other electrode, but more likely hydrogen, but in any event, at the size of operation we are using here, the quantities are negligible. You do have to rinse the object thoroughly after the process is carried out, but it’s debatable whether the very dilute salt solution needed would be a corrosion issue - around 5g in 1000ml. (The salt is only there to make the water conduct electricity a little better).
A carbon rod might be a better electrode, e.g. from an old-style U2 battery, (do they still have rods down the centre I wonder?). Maybe a carbon arc welding electrode would be an alternative, though they’re usually copper plated. The other electrode does dissolve to a point (hence the comment regarding stainless). However, it shouldn’t migrate to the item being cleaned, as that is repelling.
If you have used salt it maybe a good idea if you boil the object in distilled water, (or water from a filter jug) or if it won't stand boiling, then soak in cooled boiled distilled water, to help remove as much of the salt from pores in the surface of the item.
If there are concerns about the salt, as weak solution of sodium carbonate (washing soda) or a weak acid like lemon juice or vinegar might be good alternatives - the two latter will also brighten brass after electrolysis as well. To really brighten brass, clock cleaner (detergent + ammonia + oleic acid) does an excellent job.
Hope that's of interest - maybe those with an enquiring who wish to clean any tarnished brass items mind might wish to give it a go?
Regards, David.
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
BVWS Member.
G-QRP Club Member 1339.
'I'm in my own little world, but I'm happy, and they know me here'
