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How much does tarnish affect the conductivity of silver?


We manufacture an industrial product with silver plated contact pins. We have noticed many of the pins are tarnished. This does not seem to affect the operation. Would like to know for sure if tarnish affects the conductivity, and if so, how much?

Lowell Bonner
Manufacturing - Tulsa, Oklahoma


Tarnish reduces conductivity since it is metal oxide not pure metal. Sometimes this is not enough to cause problems depending on electric factors (voltage, amperage) or mechanical (such as relative movement that sweeps tarnish away). When absolutely no tarnish is tolerated the plating normally is gold (palladium seems to be a good intermediate compromise between tarnish resistance and cost).

Guillermo Marrufo
Monterrey, NL, Mexico


Silver sulphide(tarnish) is conductive silver compound. Compared with pure silver conductivity is reduced.

Good luck!

Goran Budija
- Zagreb, Croatia


I believe silver sulphide is a semi conductor and will therefore conduct electricity, but nevertheless it will reduce the surface conductivity of the silver. To what extent will depend on the thickness of the tarnish. Surface tranish will not affect the bulk conductivity unless the "bulk" thickness is very thin. When silver contacts are used, one of the factors that make them good is that the silver is soft and when rubbed against the other contact, it cleans itself and smears, so good metal-metal contact can be sustained. However, if the contcats are not designed to do this, there could be a longer term problem with an accumulation of low conductivity sulphides and oxides. Basically, any potential loss in conductivity depends on the design of the contact.

Trevor Crichton
R&D practical scientist
Chesham, Bucks, UK

First of two simultaneous responses -- +++++

My apologies gentlemen, they certainly are sulphides not oxides.

Guillermo Marrufo
Monterrey, NL, Mexico

Second of two simultaneous responses -- +++++

All of the above is correct. It all boils down to voltage and contact pressure. IF you do put gold over silver, be aware that the silver will walk right thru the gold in a few days, so use a barrier like nickel or palladium. IF the silver is left on top, then dip it thru one of the yellow colored slightly chrome bearing rinses in the shop and that will retard the tarnish.

Finally, silver cyanide will not rinse off in 40 rinses, you must use a neutralizer like 5% acetic acid, then top it off with a smidgen of chrome yellow water.

Editor's note:    
   Mr. Probert is the
   author of
Robert H Probert
Robert H Probert Technical Services

Garner, North Carolina

June 27, 2012

Q. I use AA silver impregnated fabric as an electroconducting surface as a switch; how can I prevent the silver oxidising and thus reducing conductivity?

Andy Houston
- Minchinhampton, England

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