Hello Laura. Yes, there is a chemical process that can produce a
fine silver powder. The material looks like cement and is called
"cement silver". I don’t know what the particle size range of
cement silver is, but it probably varies widely. I doubt very much
it would be suitable for making PMC. James Binnion gave the answer
to the practicability of making your own PMC in his post of 8-14.
The process for cement silver is very old. It is still used by
assayers and others recovering values from scrap. The process is
hazardous for those not trained in proper chemical/laboratory
procedures. I will describe the process briefly, without the many
important details, to give those interested an idea of what is
involved in one of the several processes used for recovering silver
The scrap sterling is cleaned to remove organic matter, foreign
material, etc. It is then physically processed to produce pieces
having as large a surface area as possible in a form that prevents
the material from laying flat on the bottom of the reaction vessel.
The prepared material is digested in 50 volume percent nitric
acid. This must be done carefully to control the reaction rate. The
reaction produces oxides of nitrogen, much of which is nitrogen
dioxide-nitrogen tetraoxide (NO2-N2O4). Nitrogen dioxide-tetraoxide
is a reddish-brown gas that is very toxic, suffocating and extremely
corrosive. There are laws controlling the amount and procedures for
the release of these gases. The presence of excess nitric acid is
to be avoided. It is added a little at a time. When all of the
scrap is dissolved, a piece of silver is added and then watched for
any indication of further reaction. If reaction is observed it is
allowed to proceed to completion.
The nitric acid free reaction solution is diluted with three
volumes of distilled water and filtered. At this point you have a
blue-green solution that contains silver nitrate and cupric nitrate
The filtered solution is further diluted with tap water and a
concentrated table salt solution is slowly added with stirring.
From this point on it is desirable to to keep light as low as
possible. The silver is precipitated as a white solid (silver
chloride). The precipitate is allowed to settle and the supernatant
liquid is tested to assure complete silver precipitation. The
silver chloride is filtered off and then washed with hot water until
the filtrate is colorless. A small pinch of the silver chloride is
then usually removed and tested for the presence of lead or mercury.
We would expect none using good clean sterling scrap.
The washed silver chloride is kept wet/damp and is spread out in
a glass dish and then covered with dilute sulfuric acid. The
mixture is warmed slightly and zinc (preferably zinc powder) is
added slowly with with vigorous stirring until the evolution of
hydrogen gas (very flammable!) ceases. The slurry is filtered and
washed on the filter with very dilute sulfuric acid (to remove any
excess zinc) followed by water washes until the pH is about 7. The
dried precipitate in the filter is good purity finely powdered
silver that has a grey color. Ordinarily, the cement silver is
mixed with flux and melted to cast an ingot.
"Marlinespike Seamanship in Precious Metals"