Tarnish on Silver-Plated Components: its removal - UK Vintage Radio Repair and Restoration Discussion Forum

Skywave · 31st May 2007, 6:16 pm

Preamble ~ Although this is "Cabinet / Chassis" stuff, it doesn't feature in "Domestic Radios" - but it is common in "Military Equipment" - which is why I've chosen to put it here.

I think most of us who take an interest in this Section of the Forum know what I'm referring to here: that matt, buff cream / yellow finish that you find on self-supporting VHF coils, screening cans, tuning condensers, etc. Often it has acquired a dirty finish and / or black spots where corrosion / tarnish has set in - usually, I believe, due to handling / acid on the fingers, (amongst other causes)

Question is: what is the way to remove this tarnish / corrosion without damaging the silver plating? Metal cleaner doesn't sound like a good idea, since this would surely remove the very thin layer of silver plating. I suppose that an ultra-sonic bath may do the job - but I suspect that not many of us have such a useful item.

Your thoughts, ideas, suggestions and know-how are invited. Thank you.

Al / Skywave.

OErjan_S · 31st May 2007, 6:45 pm

bakingsoda bath in a aluminium tank (or alfoil in a plastic tank) just make sure to have complete circuit and oxygen should go to the Al instead, then soak in distilled water 3-4 times to remoe the bakingsoda...

Mike Phelan · 1st Jun 2007, 8:37 am

Seconded!
I use washing soda (sodium carbonate).
This is how these "magic silver cleaning plates" work - they are just bits of aluminium sheet with a few fancy holes for effect to justify the £5-£10 charged.
Put some cooking foil in a plastic bowl, soda solution and drop parts in.

Skywave · 1st Jun 2007, 5:12 pm

Goodness me!

I never knew that trick!

Mike -
Any suggestions as to the concentration of the soda - such as x grams per litre of water?
Is the temperature of the solution relevant? - for example, I would have thought that cold would work better than hot.
Is there any benefit to be gained from using distilled / de-ionised water over common tap water?
Is it helpful to agitate the item whilst it is in the solution?

Finally - just out of interest - are there any chemists out there who can provide the chemical equations for the reaction?

Al / Skywave.

SWB 18 · 1st Jun 2007, 8:03 pm

When rebuilding high power (many kW) silver plated klystron cavities and spring fingers at work, suitably clad in rubber gloves and goggles etc, we used 'Silver Dip' liquid cleaner. It was the clear, very thin fluid type, which we applied with paint brushes or cloths.
Once clean, everything was thouroughly washed with de-ionised water and allowed to dry.

The 'Silver Dip' was said to be a 'special formula', came in 5 litre industrial containers, but seemed to smell and work just like the stuff you could buy in the High Street in small quantities.

Phil.

Skywave · 1st Jun 2007, 8:37 pm

Just a quick note to say "thank you" to all who replied to my question. I will try the suggestions and report back.

Al / Skywave.

Ray Cooper · 1st Jun 2007, 10:26 pm

Ah yes, the dread 'Silver Dip' - I remember it well...

It certainly worked - a bit pongy, though. Though its worth while examining just what is going on when you use this stuff.

'Tarnish' is generally either silver oxide or silver sulphide. The former is lightish in colour and forms a fairly even 'bloom' on the surface of the metal - simple atmospheric oxidation, though probably accelerated by other impurities in the atmosphere. Silver sulphide is darkish in colour and usually appears in quite small spots, presumably where atmospheric pollutant particles have alighted on the surface. Interestingly, both the oxide and the sulphide of silver appear to be electrically conductive, so for most people the only reason for removal will be an aesthetic one. However, conductive or not, they certainly don't conduct as well as pure silver, so if you are passing any amount of current through the oxide layer, it will tend to warm up: to the extent that spring fingers in contact with the tarnish and carrying RF currents will tend to heat up, and eventually the contact surfaces will burn. This then worsens the contact resistance even further, and a destructive runaway effect results. Hence the great keenness in cleaning klystron (and other) cavities regularly.

The trouble with the 'Dip' is that when it removes the tarnish, it removes what was formerly silver, too, so erosion of the plated surface still takes effect. The cleaned surface, in fact, looks dull - no more shine. If you examine the freshly-cleaned surface microscopically, it looks like the surface of the Moon, and while this cleaned surface now conducts properly, the roughness causes increased mechanical friction if/when you try to move the contact fingers over the surface. So when we did our cavities, we used the Dip (to get the surface clean) and then a very light application of something like Silver-Glit wadding (to polish the surface and reduce friction). Even so, after about five cleanings with this rather aggressive treatment, the plating would be starting to wear thin and the cavity would eventually need to be sent away to be re-plated.

Mike Phelan · 4th Jun 2007, 8:23 am

Quote:

Originally Posted by Skywave

Mike -
Any suggestions as to the concentration of the soda - such as x grams per litre of water?
Is the temperature of the solution relevant? - for example, I would have thought that cold would work better than hot.
Is there any benefit to be gained from using distilled / de-ionised water over common tap water?
Is it helpful to agitate the item whilst it is in the solution?

Al / Skywave.

Hi Al
I must admit that I don't bother being too critical - I just use hot water to make the soda crystals dissolve, and chuck a small handful into the water and stir it.
I might agitate it a few times.
It's probably like my cooking - I don't weigh or measure it, but it always works!

31st May 2007, 6:16 pm	#1
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Tarnish on Silver-Plated Components: its removal Preamble ~ Although this is "Cabinet / Chassis" stuff, it doesn't feature in "Domestic Radios" - but it is common in "Military Equipment" - which is why I've chosen to put it here. I think most of us who take an interest in this Section of the Forum know what I'm referring to here: that matt, buff cream / yellow finish that you find on self-supporting VHF coils, screening cans, tuning condensers, etc. Often it has acquired a dirty finish and / or black spots where corrosion / tarnish has set in - usually, I believe, due to handling / acid on the fingers, (amongst other causes) Question is: what is the way to remove this tarnish / corrosion without damaging the silver plating? Metal cleaner doesn't sound like a good idea, since this would surely remove the very thin layer of silver plating. I suppose that an ultra-sonic bath may do the job - but I suspect that not many of us have such a useful item. Your thoughts, ideas, suggestions and know-how are invited. Thank you. Al / Skywave.

31st May 2007, 6:45 pm	#2
OErjan_S Retired Dormant Member Join Date: Mar 2007 Location: Skelleftea, Sweden Posts: 250	Re: Tarnish on Silver-Plated Components: its removal bakingsoda bath in a aluminium tank (or alfoil in a plastic tank) just make sure to have complete circuit and oxygen should go to the Al instead, then soak in distilled water 3-4 times to remoe the bakingsoda...

1st Jun 2007, 8:37 am	#3
Mike Phelan Dekatron Join Date: Nov 2003 Location: Near Leeds, West Yorkshire, UK Posts: 4,609	Re: Tarnish on Silver-Plated Components: its removal Seconded! I use washing soda (sodium carbonate). This is how these "magic silver cleaning plates" work - they are just bits of aluminium sheet with a few fancy holes for effect to justify the £5-£10 charged. Put some cooking foil in a plastic bowl, soda solution and drop parts in. __________________ Mike. Last edited by Mike Phelan; 4th Jun 2007 at 8:18 am. Reason: Typo

1st Jun 2007, 5:12 pm	#4
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Tarnish on Silver-Plated Components: its removal Goodness me! I never knew that trick! Mike - Any suggestions as to the concentration of the soda - such as x grams per litre of water? Is the temperature of the solution relevant? - for example, I would have thought that cold would work better than hot. Is there any benefit to be gained from using distilled / de-ionised water over common tap water? Is it helpful to agitate the item whilst it is in the solution? Finally - just out of interest - are there any chemists out there who can provide the chemical equations for the reaction? Al / Skywave. Last edited by Skywave; 1st Jun 2007 at 5:23 pm.

1st Jun 2007, 8:03 pm	#5
SWB 18 Pentode Join Date: Sep 2005 Location: West Midlands, UK. Posts: 181	Re: Tarnish on Silver-Plated Components: its removal When rebuilding high power (many kW) silver plated klystron cavities and spring fingers at work, suitably clad in rubber gloves and goggles etc, we used 'Silver Dip' liquid cleaner. It was the clear, very thin fluid type, which we applied with paint brushes or cloths. Once clean, everything was thouroughly washed with de-ionised water and allowed to dry. The 'Silver Dip' was said to be a 'special formula', came in 5 litre industrial containers, but seemed to smell and work just like the stuff you could buy in the High Street in small quantities. Phil.

1st Jun 2007, 8:37 pm	#6
Skywave Rest in Peace Join Date: Jun 2006 Location: Chard, South Somerset, UK. Posts: 7,457	Re: Tarnish on Silver-Plated Components: its removal Just a quick note to say "thank you" to all who replied to my question. I will try the suggestions and report back. Al / Skywave.

1st Jun 2007, 10:26 pm	#7
Ray Cooper Retired Dormant Member Join Date: Jan 2007 Location: Porthmadog, Gwynedd, UK. Posts: 199	Re: Tarnish on Silver-Plated Components: its removal Ah yes, the dread 'Silver Dip' - I remember it well... It certainly worked - a bit pongy, though. Though its worth while examining just what is going on when you use this stuff. 'Tarnish' is generally either silver oxide or silver sulphide. The former is lightish in colour and forms a fairly even 'bloom' on the surface of the metal - simple atmospheric oxidation, though probably accelerated by other impurities in the atmosphere. Silver sulphide is darkish in colour and usually appears in quite small spots, presumably where atmospheric pollutant particles have alighted on the surface. Interestingly, both the oxide and the sulphide of silver appear to be electrically conductive, so for most people the only reason for removal will be an aesthetic one. However, conductive or not, they certainly don't conduct as well as pure silver, so if you are passing any amount of current through the oxide layer, it will tend to warm up: to the extent that spring fingers in contact with the tarnish and carrying RF currents will tend to heat up, and eventually the contact surfaces will burn. This then worsens the contact resistance even further, and a destructive runaway effect results. Hence the great keenness in cleaning klystron (and other) cavities regularly. The trouble with the 'Dip' is that when it removes the tarnish, it removes what was formerly silver, too, so erosion of the plated surface still takes effect. The cleaned surface, in fact, looks dull - no more shine. If you examine the freshly-cleaned surface microscopically, it looks like the surface of the Moon, and while this cleaned surface now conducts properly, the roughness causes increased mechanical friction if/when you try to move the contact fingers over the surface. So when we did our cavities, we used the Dip (to get the surface clean) and then a very light application of something like Silver-Glit wadding (to polish the surface and reduce friction). Even so, after about five cleanings with this rather aggressive treatment, the plating would be starting to wear thin and the cavity would eventually need to be sent away to be re-plated.