Tarnish

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tarnish

[′tär·nish]
(metallurgy)
Discoloration of a metal surface due to the formation of a thin film of oxide, sulfide, or some other corrosion product.
(mineralogy)
The altered color and luster of a mineral surface; characteristic of copper-bearing minerals.

Tarnish

 

the variegated, often iridescent, coloring of a thin surface layer of a mineral, differing sharply from the color of the rest of the mineral. Tarnish is caused by the presence, on the surface of the mineral grains, of a thin film formed as a result of the alteration of the mineral, for example, under exposure to oxygen. The film often produces an iridescent effect. Tarnish is typical of bornite, chalcopyrite, limonite, and other minerals. It is not observed on a fresh surface of mineral breakage.

tarnish

An oxide layer on a metal surface that causes it to dull, often discoloring it.
References in periodicals archive ?
Tarnishing of silver plated articles cannot be prevented completely; elements such as sulphur, moisture, oxygen and chlorides that accelerate tarnishing are ever present and in time, low carat gold and silver and silver plated jewellery will eventually tarnish.
To slow the onset of the tarnishing process there are some metallurgical interventions, for example the addition of de-oxidising metals such as germanium or silicon to the alloy mix.
Tarnishing is an inevitable long term reality for precious and costume jewellery items.
It is well known that recycled paper and cardboard actually has a lower sulphur content than virgin paper; additionally re-processed paper has lower levels of other harmful tarnishing causing constituents.
0002% of reducible sulphur may cause tarnishing, whereas, if the pH is higher, even a much higher quantity of sulphur may not cause tarnishing and might be tolerated.
Acid free' paper/card board is more important from tarnishing point of view.
In the UK, the average level of sulphur in the atmosphere is only a few parts per billion and this is not sufficient in itself to cause rapid tarnishing.
Some synthetic foam, besides sulphur, contains high levels of chlorides and fluorides--both of which will cause tarnishing of silver and other metals used in jewellery.
The accelerated tarnish test procedure utilised by The Laboratory of the Birmingham Assay Office for testing packaging materials involves the identification of the presence or absence of components in packaging responsible for tarnishing or staining silver products which come into contact with the packaging material.