Gold, Silver, Vermiel and tarnish

[Johnny Appleseed]

Quick question for the material's experts on the board.

 

I have found three different WWII era FPs with gold filled caps - a Parker 51 Vacumatic from 1944, and two Sheaffer Crests. All had a heavy layer of some sort of black tarnish on the GF caps. The tarnish polished off nicely, and they are beautiful pens. I have been perplexed by the tarnish, because I did not think that gold was supposed to tarnish. However, the caps really do not look brassed - it looks like the GFT is intact.

 

I understand that due to the designation of brass as a strategic metal needed for shell casings etc. during the war, many of the better FP companies switched to using vermiel - gold-filled over silver - instead of the usual gold-over brass. I also have ready, in a post from a well known pen expert whose information often needs validation, that the black tarnish seen on some vermiel pens is actually the silver tarnishing under the gold-fill.

 

Does this make sense? If not, what would cause a 1/10 GF trim to develop a black tarnish?

 

John

Edited May 12, 2006 by Johnny Appleseed

[saintsimon]

Even gold-fills themselves oxidize, as they are never made of pure gold, but contain silver, copper etc. I once had bought new gold (over brass) plated M760 Pelikan, which showed a yellowish discolouration which I had to clean off with a silver pollishing cloth. Maybe some vermeil gold layers on are not thick enough to prevent the silver underneath from oxidizing.

Edited May 13, 2006 by saintsimon

[Blorgy]

One possibility is (black) silver sulphide, which may be formed in industrial cities by the reaction of hydrogen sulphide gas with silver.

Edited May 12, 2006 by Blorgy

[NeoTiger]

I'm a graduate chemical & materials engineer. I think it would mostly depend on the quality of the gold layer. Both points that saintsimon said are possible, either the gold alloy (pure gold is way too soft) itself is susceptible to corrosion (because that's what tarnish is, just really slowly), or the gold layer does not cover the silver/brass underneath well enough (too thin, microscopic cracks, porosity, etc).

 

Gold itself is immune to oxygen (the cause of most corrosion), but common gold alloys contain copper and silver which may show response to organic sulphur that may be present in the storage conditions or chlorine (although I doubt the pens would be exposed to much chlorine) and other halogens.

Edited May 13, 2006 by NeoTiger

[Blorgy]

There is some information about tarnishing gold at:

http://www.gold.org/jewellery/technology/c...tarnishing.html

[Johnny Appleseed]

but common gold alloys contain copper and silver

 

Thanks for the responses. Copper was also, I believe, a strategic metal, but not silver - so I suspect the alloy for the 14K gold-fill may have had more silver than "normal".

 

The caps are all 1/10 Gold Filled, and don't look significantly worn, so I doubt it is caused by thin plating.

 

John