Schwerter's solution

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Schwerter's solution is a test solution for testing silver objects.

Recipe

Schwerter's solution is quite forgiving to the composition so there are a lot of different recipes on how to prepare it. Here are a couple different.

10g potassium dichromate + 22ml nitric (67-70%) + 7.5ml distilled water
HNO3 + K2Cr2O7 =Schwerter's Silver Test Solution
Add 20 grains of potassium dichromate to 30 mL of 35% nitric acid.
Dissolve Potassium Dichromate salt in 8mL of distilled water in a glass container.
Add crystals until no more salt will dissolve in the liquid.
Add 25mL of 70% Nitric Acid
Store in a small bottle.

Detailed instructions

To test an object a notch is filed into the object, at least so deep that any heavy plating is penetrated. A drop of the solution is applied and the color during the first minute is observed and the mark left by the test. Different alloys and metals will give different colored reactions.

Alloy / metal Color after a minute Color of mark left
Pure silver Bright blood-red Grayish white
.925 silver Dark red Dark brown
.800 silver Chocolate brown Dark brown
.500 silver Green Dark brown
German silver Dark blue Light gray Scarcely any
Nickel Turquoise blue
Copper Brown Cleaned copper
Brass Dark brown Light brown
Lead Nut brown Leaden
Tin Reddish brown Dark
Zinc Light chocolate Steel gray
Aluminum Yellow No stain
Pure gold No reaction
Palladium None
Platinum Vandyke brown No stain
Iron Various Black

Table thanks to Geo and Lazersteve

Referenses

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