Antiques, their restoration and preservation / by A. Lucas.

  • Alfred Lucas
Date:
[1932]
Catalogue details

Licence: In copyright

Credit: Antiques, their restoration and preservation / by A. Lucas. Source: Wellcome Collection.

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    soft brush. If the tarnish still persists, the next step is to apply dilute ammonia solution (10 parts of strong ammonia, specific gravity -880, to 90 parts of water) with a rag or small sponge, which removes silver chloride, often the chief constituent of the tarnish. In the rare cases in which ammonia is not successful, potassium cyanide 1 should be tried, as this will remove tarnish due to silver sulphide and copper sulphide, which are not soluble in ammonia. This reagent should only be employed in very dilute solution (5 per cent.), as it acts upon and dissolves gold when used too strong, or if left in contact with the gold too long. After treatment, the object must be thoroughly washed in warm water and carefully dried. Occasionally on the surface of ancient gold there are patches of a dark purplish discoloration apparently due to organic matter, which is not soluble either in ammonia or in potassium cyanide, but which can sometimes be removed by the care¬ ful use of plate powder, such as whiting or jeweller’s rouge, or sometimes by heating, if the nature of the object will allow of this, which is done by making the object momentarily red hot in the flame of a bunsen lamp or spirit lamp. If, how¬ ever, the gold is very thin it should not be heated, or it may melt. If, after heating, the gold shows 1 This reagent is very poisonous.
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