What is the chemical equation for the oxidation reaction between Silver and Potassium Polysulphide?

Question

also if potassium has more than one polysulphide, what are their recations with silver? Can I control the colour change produced on the surface of the silver by controlling (for eg) Ph? I want the reaction to stop when the silver becomes irridescent blue and purple to obtain consistency between pieces (I'm a jewellery making ex-chemist!!) without the trial and error I currently rely on!

Answer 1

///// the following applies to copper and bronze, but will most likley work with silver, too.

A. Ammonium Sulfide Process

With a sponge or pad fairly well wrung out, swab on a thin film of a solution containing 5% to 10% by volume of polysulfide (dark) and water.

Rinse thoroughly.

Immediately follow this with a slightly heavier film of either a 5% solution of copper sulfate in water or a 0.5% solution of sulfuric acid in water. Apply by swabbing with a sponge or pad.

Do not contaminate the solutions by using the same sponge to apply both.

Rinse thoroughly.

Tone by rubbing in the direction of the grain with a fine abrasive pad (e.g., Scotch-Brite) while still wet.

Remove solution residue by wiping with a clean damp cloth or sponge and dry.

Repeat until the desired depth of color is achieved.

Alternatively, small objects may be immersed in the ammonium polysulfide copper sulfate solutions.
B. Potassium Sulfide Process

One gallon of 1.5% sharp water (2 oz oxalic acid in 1 gallon tap water).

Fine beach sand.

Potassium sulfide (liver of sulfur) mixed in tap water (1/4 lb. liver of sulfur to 1 gallon water).
Clean the metal. Wipe down the solution of potassium sulfide using a virgin clean white cloth, in the direction of the grain of the metal. Wash down with a clean white towel wrung out in sharp water. Apply fine beach sand with another clean wet towel going against the grain to even out the color.

This procedure is followed until a medium statuary color is attained. It may have to be repeated several times before uniformity appears. After the desired uniform color is attained, neutralize the work with a wash of clear water.

C. Other Processes/Procedures

Clean with fine pumice (0, 1/2) on a clean cloth moistened with a 10%-20% solution of oxalic acid and water.

Wipe off with a clean soft cloth

Apply a 5%-l 0% solution of potassium sulfide or ammonium sulfide using another soft cloth dipped in the solution and well wrung out.

Follow while still wet with a wipe of sharp water (about 2 oz of oxalic, sulfuric, or nitric acid in 1 gallon water) using a clean soft cloth well wrung out.

Repeat steps 3 and 4 to achieve a depth of color slightly darker than the desired shade.

Relieve the surface by rubbing with fine beach sand on a clean damp cloth until the desired color is reached.

Rinse and dry.

Answer 2

I am not familiar with the potassium ,but any thing with sulfur in it will tarnish silver . I lived in the West Texas oil field and they have H2S very deadly gas. So they burn it and it makes SO2 and that will tarnish all silver ,the better quality the more tarnish . Try to get Camphor Gum . It looks like small sq. of paraffin and smells like Camphor. Some way if u put it in a drawer it retards the reaction of the sulfur .

Answer 3

probably immersion in a diluted solution for a fixed amount of time, then immediate rinsing should have a good reproducibility.

Check also the temperature, maybe doing it at low temp will slow the reaction enough to have the desidered result/color.