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Cheaply assay unknown metal?


#1

Hello everyone!

I recent purchased an assorted box of used jewelery tools at an
auction. When I got home with the box I discovered a sizable sheet of
metal in the bottom that was sandwiched between two sheets of
cardboard. I hadn’t even noticed it at the auction because it was flat
against the bottom and I assume that no one else noticed either because
I got an excellent bargin on what I Knew was in the box. My question is
this: Is there an easy way for me to find out what type of metal it
is? At first I thought it was silver but I detect a light golden sheen
(my eyes are not that great any more so I may be mistaken). I work in
silver so I don’t have any gold assay kits. Then again it could be
some base metal alloy. I just don’t know! Any help is greatly
appreciated!

Thanks!
Shane Morris
Druid’s Grove Unique Gifts


#2
 Is there an easy way for me to find out what type of metal it is?
At first I thought it was silver but I detect a light golden sheen 

G’day; Yes there are a few simple tests you can do. First cut a
small sliver off hold it briefly in a flame (using pliers!!) and
immediately dip it into some solid table salt. Now carefully reheat
it in the edge of the flame. the salt will produce a very bright
golden flame, but if should you see a greenish tinge, then it will
contain copper, and may be brass or low carat gold, but more likely
just brass. It will also go black, whereas pure gold won’t. Pure
silver will remain virtually unstained, but sterling will go black,
and that blackness is mainly due to the formation of copper oxide on
the surface. Pickle will of course remove that, and if you have
sterling, the resultant surface will be white.

If you want to take this kitchen sort of chemistry/‘assay’ business a
little further, dissolve a tiny piece in warmed strong nitric acid;
don’t breathe in the brown fumes of nitric oxide as it is quite
poisonous, but the small amount you make won’t be noticed in good
ventilation. Add a little salt solution to the liquid. If the metal
contained silver you will get an opaque white precipitate of silver
chloride which turns a dirty violet on exposure to sunlight. Now
carefully add a little ammonia. The solution will get very hot as the
acid and alkali neutralise and react together. Keep adding ammonia
and shaking, and the precipitate will completely dissolve. You have
proved that silver is present. If copper is also present, the further
addition of ammonia will produce a pale blue colour, thus proving you
have sterling. If you’re sure there is no blue colour, then you have
fine silver. If you have gold the sliver of metal won’t react. If it
should be one of the many varieties of brass, then it will dissolve
easily in nitric acid, and will give a solution with a definite blue
colour. The addition of excess ammonia will give a deep blue colour
indicating that the metal contains a good deal of copper.

You should also bear in mind that a sheet of sterling or even fine
silver, if left as you have found it for any length of time, will
accumulate a fine golden sheen due to a very slight reaction with
minute amounts of sulphur in the atmosphere and the cardboard. (which
may contain the remnants of sulphite bleach) Cheers and happy assay, I
say.

John Burgess; @John_Burgess2 of Mapua Nelson NZ


#3

John,

I have a further question. I did the flame test you recommended and
I am pretty sure there is no copper present. I also tested some
jewelers brass and sterling silver so I could compare the reaction of
my unknown metal to known metals. As expected the Brass and sterling
turned black. My unknown metal was not tarnished at all however it
did change colors. They were tempering colors (golden to green). One
other thing I noticed was the rate at which the different metals
reached the cherry red state. NOTE: All samples were approximatly the
same size and I was useing propane torch to do this test. The brass
and sterling both went cherry red very quickly. My mystery metal
required a good deal of time to even begin to glow. Any thoughts?
Thanks!

Shane Morris


#4
    I have a further question.  I did the flame test you
recommended and I am pretty sure there is no copper present.  I also
tested some jewelers brass and sterling silver so I could compare
the reaction of my unknown metal to known metals. As expected the
Brass and sterling turned black.  My unknown metal was not tarnished
at all however it did change colors. They were tempering colors
(golden to green). 

G’day Shane Morris; Those colours were almost certainly produced by
surface oxidation, and as you say, like tempering colours.

    One other thing I noticed was the rate at which the different
metals reached the cherry red state. 

This effect is certainly due to the metals having different
coefficients of heat conduction and also differing specific heats -
that is, it takes a greater amount of heat to get 1 gram of steel to a
certain temperature that it takes for 1 gram of say, aluminium. This
property is linked to specific gravity also.

   My mystery metal required a good deal of time to even begin to
glow. Any thoughts? 

If you would like to go to the trouble you could cut strips of
different metals of the same thickness, width and length, clamp one
end between two pieces of steel plate and place a piece of bees wax or
candle wax on each of the other ends. Heat the steel and take the
time at which each piece of wax melts. This gives a fairly accurate
indication of specific heat. Stainless would be one of the last to
melt the wax. Silver would be one of the first

One can’t be too certain without facilities for actual chemical
analyses, but it does seem to me that your metal probably contains
nickel, very likely in the form of stainless steel which does have
low heat conduction properties. Whilst not all stainless steels are
attracted by a magnet, many are, but the better ones have no ferro
magnetic properties. A cobalt/nickel alloy would be very slightly
magnetic. (I’ve got that in both my knees!)

Most of the alloys containing a high proportion of nickel (such as
stainless) tend to be relatively poor conductors of electricity, but
there again, you really need fairly sophisticated equipment to
determine that.

If you can dissolve a very small amount of the metal in a little warm
nitric acid, or even 10% sulphuric acid, nickel gives a pale green
colour. There is a colour test for nickel which requires a chemical
not easily obtainable called dimethylglyoxime, which gives a bright
red colour to solutions containing nickel - but that’s not much use to
anyone outside a lab!

There is one more possible test open to you; make a 3mm loop at one
end of of thin (say 22 gauge) iron wire, make it red hot and dip into
powdered borax and repeat until you have a nice little bead. Touch
the hot bead into very fine filings of the metal and reheat strongly.
The presence of nickel is indicated by a green colouring of the bead,
but there are other metals which also give a green borax bead under
certain conditions, so this isn’t positive. Other than these
suggestions, I cannot help you identify your unknown metal positively.
Sorry, but cheers just the same. –

John Burgess; @John_Burgess2 of Mapua Nelson NZ