by Tony Clayton.
This page details the various metals and
alloys that have been used for coins and medals over the centuries.
When I was at University I gave a talk to
the college Science Society on the subject, and it is also of interest to
me as my first job involved carrying out research into alloys of such
exotic materials as niobium, hafnium, tantalum, zirconium and titanium for
superconducting, chemical and aeronautical applications.
We also had some gallium, but somebody left
it above a radiator and it melted!
Some (but by no means all) of the
information came out of 'The Teach Yourself Guide to Numismatics' by
C.C.Chamberlain published in 1960, and I also wish to acknowledge the help
of many correspondents on the newsgroup rec.collecting.coins.
Additional information has been gleaned
from an article published in World Coin News (February 17 1992 and March 2
1992) entitled 'World's coinage uses 24 chemical elements' by Jay and
Marieli.
The following materials are covered in this
document:
Element (Al), Atomic No. 13, density 2.70
kg/litre, M.Pt 660°C
The metal was first prepared by Oersted and
Wohler in 1824.
A very 'white' corrosion resistant metal
(called aluminum in the USA) used for cheap coins in a number of
countries, particularly in Europe where inflation had decreased the value
of money. Recent examples include the tiny 1 peseta coin issued by Spain,
and the 5 and 10 lire coins of Italy.
The pure metal is very soft, and so does
not wear well. However, it is an important alloying addition (see Aluminium
Bronze).
There is an apocryphal story that the
absence of the second letter i in the American spelling was the
consequence of a signwriter misspelling the word when the first producer
of aluminium started up in the US! After all, the Americans don't use the
words sodum, potassum, chromum or titanum, do they? However, I gather that
this tale is an urban legend!
Alloy
Copper-aluminium alloys, sometimes
containing a small amount of manganese or nickel.
They are yellow in colour and hard wearing. A modern example of its use is
with the 5, 10 and 20 centime coins of France.
A variety called Nordic Gold is apparently
being used for some Scandinavian coins, and also for the new 10, 20 and 50
eurocent coins because it does not contain nickel. It has a composition of
89% Cu, 5% Al, 5% Zn and 1% Sn.
Element (Sb), Atomic No. 51, density 6.62
kg/litre, M.Pt 631°C
Known since ancient times.
A silvery metal which is very brittle, and
is easily crushed and powdered, and is thus an unlikely candidate for use
in coins. It is easily cast (melting at 631°C), and gives a clear
impression of the mould. Its main use is as an alloying addition used to
harden lead.
The only example of which I am aware of the
use of antimony for an issued coin is a 10c piece struck(?) in China in
1931.
A pattern in this metal of a penny, struck
in 1860, has recently been put on sale by Spinks of London.
It is used alloyed with tin,
copper or lead to produce white
metal used in the manufacture of medallions.
Composite
Barton's Metal is in fact copper overlaid
with a thick layer of gold, and was used in 1825 during the reign of
George IV for pattern five pound and two pound coins by the Royal Mint.
Alloy
A type of cheap bronze
used in the manufacture of some Irish and American tokens, and for some
coins of the Isle of man.
Alloy
A type of bronze
normally used in the manufacture of bells, but also used in France at the
time of the Revolution.
Alloy
An alloy of copper and silver,
with more than half copper. Large quantities of billon coins were produced
in the Roman era, many with a silver wash. This alloy was also used by the
French during the 18th century.
Alloy
An alloy of copper and zinc,
although the term is loosely used to include all copper alloys. Generally
the alloys used vary in composition from 3% zinc to 30% zinc, and vary in
colour from the red of copper to a bright yellow.
Brass with a small quantity of nickel
is known as Nickel Brass. Such alloys are used for the
modern UK one pound coin.
The Roman name for the brass alloy used in
coins was Orichalchum
In Old English the Latin word aes was
rendered as brass, thus the use of the word brass to mean money still
found today, especially in Northern England. Many brass coins have been
produced in modern times, although more complex copper alloys are normally
used.
Various forms of brass have been used to
make fake gold coins to deceive gullible collectors (the density is
totally wrong), and I have been informed that a brass with 15% zinc is
sometimes known as Goldine in the USA.
Alloy
An alloy of copper and tin,
usually 80% to 95% copper. Most modern 'copper' coins are actually bronze,
as pure copper is too soft and rapidly shows extensive wear. While bronze
is usually copper coloured, a high tin content will give a silver colour,
as in speculum.
Bell Metal and Bath
Metal are other types of bronze.
Element (Cr), Atomic No. 24, density 7.19
kg/litre, M.Pt 1875°C
First isolated in 1798 by Vauquelin.
A hard white metal which is unsuitable for
coinage, but which has been used to plate steel coins. An example of such
use is the Canadian 5c pieces of 1944-45 and 1951-1954, which were
nickel-plated steel with a surface plating of chromium to add wear
resistance. A few medals have been struck in chromium.
Chromium is an important constituent of the
alloy Stainless Steel and is also used in smaller
concentrations to impart hardness to steels. It is not usually used in its
pure form as it has too high a melting point to cast easily, and is too
hard to work.
Element (Co), Atomic No. 27, density 8.85
kg/litre, M.Pt 1495°C
First isolated in 1733 by Brandt.
A steel-grey metal with a reddish tinge
which is strongly magnetic. It is normally used as an alloying addition.
35 medals were made in this metal for a conference on cobalt, and are
thought to be the only examples of this element's use in the pure form.
Element (Cu), Atomic No. 29, density 8.96
kg/litre, M.Pt 1083°C
A soft reddish metal known since ancient
times. It is rarely used unalloyed in modern coins, other than as a
coating for other metals (modern US cents and the UK 1p and 2p are
examples), because it has relatively poor wear properties. The beautiful
large British pennies of Queen Victoria from 1839 to 1859 were made of
copper.
One of the largest conventional copper
coins that ever circulated is the Cartwheel twopence of 1797 produced by
Matthew Boulton at the Soho Mint in Birmingham. Swedish plate money issued
from 1644 to 1759 consisted of large lumps of copper cut roughly into
squares weighing up to 6 pounds (3 kg) and 10 in (25 cm) across. They were
issued because of a grave shortage of silver after a war with Denmark. I
bet they wore holes in Swedish pockets!
It is the main constituent of a wide range
of alloys such as aluminium bronze, brass,
bronze, cupro-nickel, gun
metal, Orichalchum, and Pinchbeck.
Alloy
Gold with 2 carats of alloy and 22 carats
of gold so called from the gold crown of 1526 which used this alloy.
Previously gold coins were made from almost pure gold.
Crown gold is the standard used in the British sovereign which is still
minted. The alloying metal is usually copper, although silver has been
used.
Alloy
Self-evidently an alloy of copper
and nickel, it is one of the most common alloys used in
modern coins. It is also called copper-nickel in the US by some. A related
alloy called Alpaca also contains zinc.
It is silvery in appearance and hard
wearing, and yet easy to fabricate. In the UK was first used in 1947 where
an alloy of 75% Cu and 25% Ni is used for most 'silver' coins. With this
composition the coin shows no trace of the colour of its main constituent.
Other copper-nickel alloys have been used.
The early US cents from 1857 to 1864 contain 87.5% Cu and 12.5% Ni, and so
have a light yellow colour, while the present-day 20p coin of the UK is
made from an 84% Cu and 16% Ni alloy. Some modern cupro-nickel coins of
Russia also contain zinc. The Franklin Mint in the USA
have developed a cupro-nickel alloy they call Franklinium.
Alloy
This naturally occurring alloy of
approximately 75% gold with 25% silver
and copper and other metals was used for the earliest
coins struck in Lydia around 700 BC. The name electrum is also used for an
artificial alloy such as used for coins in the Merovingian Dynasty of the
Kingdom of the Franks around 600 - 700 AD.
It might be argued that coins made at
private mints in the US from native gold at the time of the gold rush in
California are made from electrum.
Element (Au), Atomic No. 79, density 19.32
kg/litre, M.Pt 1063°C
Gold is the most anciently known of metals,
occurring as the native metal.
Perhaps the most ideal metal for coins, as
it is malleable and chemically inert, to the extent that gold coins
discovered after long periods in the ground still maintain their lustrous
appearance. As it is a soft metal it is nowadays almost always used
alloyed with copper to make it more durable, although
gold-silver alloys have been used, particularly by Australia in the
manufacture of sovereigns and half-sovereigns during the period 1855-1870.
At present the only gold coins minted are
for bullion purposes, guaranteeing fineness and weight.
Early english coins were made of pure gold,
but a number of other alloys have been used, examples including Crown
Gold and Electrum.
Alloy
An alloy of 88 % copper,
10% tin and 2% zinc, used for making
cannons. Not normally used for coins, although the famous Gun Money was
produced from 1689 by James II for use in Ireland. It was cast in scrap
metal from old cannons, bells, etc., and is unusual in having the month as
well as the year of issue indicated. Imagine collecting Lincoln cents from
1909 to date if there were 12 different coins per year (or more if you
include mint mark variations)!
Element (Hf), Atomic No. 72, density 13.09
kg/litre, M.Pt 2222°C
First isolated as recently as 1923 by
Coster and Hevesy.
Fred Zinkann has struck a few private
pattern 'coins' in this metal, which has few uses except in the nuclear
industry, where its high neutron capture cross-section makes it useful for
control rods in some nuclear reactors.
Hafnium is chemically very similar to zirconium
with which it is normally found in nature. Indeed, zirconium ores always
contain hafnium in a proportion of between 0.7% and 50%.
As mentioned above, hafnium absorbs
neutrons very readily, whereas zirconium does not. The
need to remove hafnium from zirconium for nuclear applications is one
reason for the high cost of the latter material.
Element (Fe), Atomic No. 26, density 7.87
kg/litre, M.Pt 1537°C
First isolated in prehistoric times, for
many years iron was not used as currency as it was heavy, brittle in the
most commonly available cast form, and liable to rust.
(Before someone tells me that copper and
gold are denser, I mean heavy in terms of its weight per unit value.)
Cast iron contains between 3% and 4.2% C,
melting at between 1150°C and 1250°C, depending on the carbon content.
Iron alloys containing small levels of carbon are normally called steel.
Iron coins were issued by Finland between
1943 and 1953, and also Bulgaria in 1943.
To get round the corrosion problem in
modern coins various coatings have been used, from copper
(modern UK 'coppers') and brass (German 5 and 10
pfennig) to nickel and chromium
(Canadian post-war 5 cents), nickel alone (Finnish 1
& 5 markaa 1953-1962) or zinc (US cent of 1943).
Some of these have actually got a steel rather than
iron core.
Element (Pb), Atomic No. 82, density 11.36
kg/litre, M.Pt 327°C
Lead is a very soft bluish-grey metal, and
so early lead coins do not survive too well. However, it has been used,
particularly in southern India around the time of Christ, in China, and in
Burma and Siam during the 19th century. Because it casts well and has a
silvery appearance when new it has often been used for forgeries,
especially when plated to replicate gold coins.
In Roman times lead was used for tesserae,
which were tickets or tokens (also made in bronze) that were distributed
by the emperor (amongst others) entitling the holder to either food or
money.
In its normal state it tarnishes rapidly to
a dark grey colour, and has extremely poor wear resistance.
Element (Mg), Atomic No. 12, density 1.74
kg/litre, M.Pt 650°C
First isolated by Black in 1755.
Magnesium is a silver-white ductile metal
40% lighter than aluminium. It is an important alloying addition in many
metallurgical applications, but it has not been used for a major national
coinage issue, as far as I am aware.
There have been some minor issues - the Jay
and Marieli article refers to a 10 pfennig Lodz Ghetto issue.
The Dow Chemical Company struck some tokens
in Dowmetal, an alloy of this metal with 95% Mg, in 1933.
Element (Mn), Atomic No. 25, density 7.43
kg/litre, M.Pt 1245°C
First isolated by Gahn in 1774.
A grey metal resembling polished steel. It
is not used as a pure metal in coins or medals because it reacts with
water, but often found in alloys. The WWII 5c pieces of the USA were made
from a 56%Cu 35%Ag 9%Mn alloy from 1942 to 1945 as nickel is a vital
material in war. I am grateful to Louis S. Flocco of the USA for the
information that this alloy was chosen in order to match the electrical
properties of the original cupronickel alloy so that it could be used in
pay telephones and other vending machines.
Alloy
Technically a nickel brass containing an
additional amount of manganese. It is a copper alloy
containing zinc, manganese and a small
quantity of nickel which is used for the new US dollar.
The composition used for the dollar is 88.5% Cu, 6% Zn, 3.5% Mn and 2% Ni
overall, with a cladding of 77% Cu, 12% Zn, 7% Mn and 4% Ni. This
combination was chosen in order to match the electrical properties of the
earlier Susan B. Anthony dollar to avoid costly changes to vending
machines.
Element (Mo), Atomic No. 42, density 10.22
kg/litre, M.Pt 2610°C
First isolated in 1781 by Hjelm.
An silvery-white element usually used as an
alloying addition to steels and titanium alloys, although there are
applications where the pure metal is used. It has not been used for
circulation coins, although a small number of patterns have been made in
this metal by Fred Zinkann.
Element (Ni), Atomic No. 28, density 8.90
kg/litre, M.Pt 1453°C
First isolated in 1751 by Cronstedt, an
event commemorated by Canada in 1951 with a special 5c piece. However, the
element is present in alloy form in early Bactrian coins dating from about
200 BC.
Usually used in an alloy with copper
(see cupro-nickel) or iron (see stainless
steel), although the pure metal has been (and is) used a great deal,
notably for the coins of Switzerland and Canada. It was first used in this
form by Switzerland in 1881. The pure metal is magnetic, and is noticeably
yellower than some of the silvery metals such as chromium
and aluminium.
There is some concern that a number of
people are allergic to nickel, thus the avoidance of this element in
alloys used for the new euro coins.
Alloy
A copper alloy containing
zinc and a small quantity of nickel
which is used for the UK 'brass' threepenny bit and the pound coin. The
composition used for the threepenny bit was 79% Cu, 20% Zn and 1% Ni,
while that for the pound coin and early single metal two pound coins is
70% Cu, 24.5% Zn and 5.5% Ni. The outer ring of the bimetallic two pound
coin is 76% Cu, 20% Zn and 4% Ni.
Alloy
A copper alloy containing
18-22% nickel, 15-20% zinc and
sometimes manganese and other metals which is made with
a wide variety of compositions.
The alloy is sometimes known as German
Silver or Argentan.
Element (Nb), Atomic No. 41, density 8.57
kg/litre, M.Pt 2468°C
First isolated in 1801 by Hatchett.
An expensive grey metal mainly used for
superconducting applications in alloy form. The occasional medal has been
made using this metal. This element used to be called Columbium (symbol Cb)
in the USA.
Trials using this metal have been carried
out at the Sherritt Mint in Canada, and at the Philadelphia Mint in the
USA.
Alloy
A word used by the Romans to denote their brass,
containing 80% copper and 20% zinc,
approximately. The dupondius was distinguished from the as by being in
orichalchum rather than copper, as well as by having the emperor with a
radiate crown, whereas the sestertius, also in orichalchum, was larger. (1
dupondius = 2 asses, 1 sestertius = 4 asses, 1 denarius = 16 asses)
Element (Pd), Atomic No. 46, density 12.02
kg/litre, M.Pt 1552°C
First isolated in 1803 by Wollaston.
A scarce ductile metal of the platinum
series which does not have quite the same economic importance of platinum
at present. Some bullion coins have been made of this metal, the first
being the 1967 ½ Hau from Tonga which was actually an alloy containing 2%
ruthenium.
Alloy
Originally an alloy of tin
with about 15% lead, and sometimes antimony
and copper. Modern pewters are usually lead-free.
Pewter coins include the 1757 1 kreuzer of
Bohemia and a 5 franc French piece of 1831.
Alloy
A cheap brass, mainly copper
with some zinc, invented in the 18th century as a cheap
imitation of gold. Used for medals rather than coins. Now known as Gilding
Metal.
Element (Pt), Atomic No. 78, density 21.45
kg/litre, M.Pt 1769°C
First isolated in 1735 by De Ulloa.
Discovered in quantity in Russia in about
1822, and used by that country during the period 1828 to 1835 for coins.
Platinum is the most common of the platinum group of metals, and is
ductile, making it relatively easy to make into coins. However, supplies
are relatively limited, and the metal has a far more important use as a
catalyst in chemical reactions.
It is seen as a bullion metal as well as an
important metal for chemical applications, and a number of bullion coins
have been struck.
One of the earliest uses of platinum for
medals was in France during the Napoleonic period around 1800. I am
indebted to David Block of the USA for this information.
Alloy
An ancient alloy of copper,
zinc, lead and tin
found in coins of Ancient Gaul. Unlike billon, it normally contains no
silver, although some alloys containing silver have also been called potin,
such as some from Egypt in the 1st to 3rd century A.D.
Apparently this alloy was also used in 1st
century coins from southern India.
Element (Re), Atomic No. 75, density 21.04
kg/litre, M.Pt 3180°C
First isolated in 1925 by Noddack, Tack and
Berg.
Fred Zinkann has struck a fantasy coin in
this very scarce white metal.
Element (Ag), Atomic No. 47, density 10.49
kg/litre, M.Pt 961°C
An attractive white metal extensively used
for coins from ancient times to the present day, although the increasing
value of the metal has meant that few countries now use it except for
proof specimens. It is harder than gold, but is easily worked. Unlike
gold, it tarnishes readily if there is sulphur in the atmosphere. It
recent times is was normally used in alloy form.
Mexico issues composite coins with a .925
silver centre. As far as I am aware this is the only country using silver
for circulation coins.
Alloy
A large number of silver alloys have been
used over the years. A silver-lead alloy has been used in Bhutan.
Sterling silver (92.5% Ag) is usually
alloyed with copper. This alloy was used for British silver coins up until
1920.
During 1920 the silver content was reduced
to 50%, with 40% Cu and 10% Ni. It was found that this alloy tarnished
badly, going an unattractive yellow-brown colour, so the alloy was changed
to 50% Ag with 50% Cu. This in turn was changed to 50% Ag, 40% Cu, 5% Ni
and 5% Zn in 1927, with a significant improvement in appearance.
Alloy
A silvery alloy of tin
and bronze used in Gaul and Britain during the
period around the time of Caesar's invasion.
Alloy
A hard-wearing alloy of iron,
chromium and nickel. The 50 and 100
lire coins of Italy use this material. Because it is a hard material, and
thus fairly difficult to strike, you usually find that stainless steel
coins have a fairly low relief.
The alloy used by Italy is sometimes known
as Acmonital, an acronym for Aciaio Monetario Italiano
Alloy
A general name given to iron-carbon alloys
having smaller amounts of carbon than cast iron. Strictly speaking most
modern iron coins are made of steel. Steel rusts very
readily so it needs a coating when used for coins.
Nickel and copper
clad steel coins were in use in Bolivia from 1965 to 1987, when
hyper-inflation led to a new series of stainless steel
coins.
Zinc coated steel was
used for 2 Franc coins during the Allied Occupation of Belgium in 1944.
They were made from the same blanks as the zinc coated steel US 1 cent
piece of 1943.
The 'bronze' coinage of the UK has been
copper-clad steel since 1992, with a couple of minor exceptions.
Element (Ta), Atomic No. 73, density 16.6
kg/litre, M.Pt 2996°C
First isolated in 1802 by Ekeberg.
A hard blue-coloured metal with a very high
melting point. Too expensive and difficult to work for coinage, but once
again Fred Zinkann has made a medal in this material.
Element (Te), Atomic No. 52, density 6.24
kg/litre, M.Pt 450°C
First isolated in 1783 by Muller.
A hard grey semi-metal, or metalloid,
similar to selenium but not used for coinage. However,
in an alloy with 11% copper it has been used for a
commemorative medal.
Element (Sn), Atomic No. 50, density 7.30
kg/litre, M.Pt 232°C
Silver-like in colour and very malleable,
but too soft to stand up to wear, and the metal is more often used as an
alloying addition in copper to make bronze.
One such alloy, known as speculum,
was used by the Belgic people of Gaul and Southern Britain during the two
centuries before the birth of Christ.
Farthings and halfpennies were struck in
tin with a central copper plug in England during the 17th century. The
intention was to try and deter forgers, but the experiment was not a
success.
The metal has two (or perhaps three)
allotropic forms:
- Grey tin, stable below 13.2°C, which is
a grey powdery substance.
- White tin, stable from 13.2°C to 161°C,
which is the normal white metallic form.
- Rhombic tin, stable above 161°C to the
melting point, another metallic form, has been referred to in some
sources. I have no clear evidence for this form.
Thus on an ordinary English winter day
white tin should turn into a grey powder. In fact this does not happen
unless in extreme cold, but once some is formed, the transformation is
more rapid, giving rise to what is known as tin-pest. I have heard it said
that Napoleon's troops invading Russia in 1812 had tin buttons holding
their trousers up, with disastrous consequences when winter set in!
Tin was used for coins in Thailand in the
mid 1940's, but then the temperature does not fall so low there. Japan
used a tin-zinc alloy in 1944.
When a rod of tin is bent, it emits a
characteristic noise known as the 'Cry of Tin'. However, this phenomena
has also been observed with other elements, particularly cadmium.
Element (Ti), Atomic No. 22, density 4.51
kg/litre, M.Pt 1668°C
First isolated in 1791 by Gregor.
Titanium is a strong light metal that is
corrosion resistant. It could be used for coins, and has been used to
strike medals. However, there are problems in producing a sheet of the
metal with a smooth enough surface for coinage purposes, and this
increases the cost of producing coins in bulk using this metal. As the
basic cost of the raw metal is high as well, other cheaper alternatives
are more attractive to governments!
I have a few tokens struck in this metal
during trials at Imperial Metal Industries Ltd. Birmingham during the late
60's.
Apparently a new zinc-titanium alloy has
been developed for coinage, but no information as to its use is available.
Alloy
Tombac is a brass
alloy famous in numismatic circles for its use by Canada in the emergency
5 cent coins of 1942 and 1943, but more generally known for its use in
cheap jewellry. The particular alloy used by Canada was 88% copper with
12% zinc.
Element (W), Atomic No. 74, density 19.3
kg/litre, M.Pt 3410°C
First isolated in 1783 by D'Elhuyars.
Tungsten is a very hard and brittle metal
at room temperature, and is consequently unsuitable for coinage. It is
very dense (although not the densest material known), and has the highest
known melting point of any metal. Despite these well-known properties, I
am told that the US mint tried to make some patterns using tungsten. The
dies did not make much of an impression.
Fred Zinkann has made a pattern coin out of
an alloy containing 5% Ni, 3% Fe with smaller quantities of copper and
cobalt. The dies reputedly broke after three coins had been made.
Element (V), Atomic No. 23, density 6.1
kg/litre, M.Pt 1900°C
First isolated in 1831 by Sefstrom.
An element very similar to titanium. A
token has been struck by Wah Chang Albany to demonstrate their ability to
work in this metal, but no circulating coins have been been struck in this
poisonous metal.
Alloy
Virenium is a German Silver
type of alloy containing nickel as well as copper and zinc with a magnetic
element as a built in security device. It was first used by the Isle of
Man. It has the composition 81% Cu, 10% Zn and 9% Ni. (I am indebted to
Jrgen Smod and Louis Carlson for the latter information).
Alloy
A name given to a range of alloys usually
containing antimony alloyed with tin, copper
or lead to produce a white silvery metal used in the
manufacture of medallions.
Element (Zn), Atomic No. 30, density 7.13
kg/litre, M.Pt 420°C
First isolated in 1746 by Marggraf.
A lightweight metal which is cheap and can
readily be made into coins. It does oxidise steadily and inexorably, and
so is not a very satisfactory coinage metal in its pure form. Generally
superseded by aluminium, zinc was used by the Germans for occupation
coinage during the two world wars. The metal is an important constituent
of brass.
Element (Zr), Atomic No. 40, density 6.49
kg/litre, M.Pt 1852°C
First isolated in 1789 by Klaproth.
Similar to Titanium, and used for
flash-bulbs and nuclear fuel-rod casings. No true coins have been struck
in this metal, but a token has been struck by Wah Chang Albany to
demonstrate their ability to work in this metal.
Element (C), Atomic No. 6, density 2.25
kg/litre (graphite), M.Pt 3727°C
A small number of 'coins' were struck using
coal during Germany's hyperinflation period in 1922 as Notgeld.
The Japanese circulated a baked clay 1 sen
coin just before the end of the Second World War.
A variety of fibres were used to make coins
in a province of China.
Small glass tesserae of the 1st to 4th
centuries AD have been found in Egypt, and were probably used as coins. It
is also believed that glass weights found in Arabia were used as currency.
Embossed pieces of leather have been used
during a number of sieges around the 16th century, and examples of leather
tokens are known from Germany after the First World War.
Well, not coins but certainly bank-notes,
and Russia allowed postage stamps to act as 'coins' at one time. I have
been told that cardboard was used the Netherlands in 1574, in Mexico in
1915, and also in Germany during the notgeld issues after the First World
War.
Frequently used for tokens. The Sixth-Form
Club at Charterhouse (where I used to teach) uses plastic coin-like tokens
for change, and some transport tokens were made in this material. Further
examples are Australian Keeling-Cocos tokens of 1913 and 1968.
Australia issues plastic banknotes.
Porcelain tokens are believed to have been
used in Ptolemaic Egypt. Porcelain coins were used in Thailand in the
early 18th century, and made as Notgeld in Germany.
Element (Se), Atomic No. 34, density
4.45(r) or 4.79(g) kg/litre, M.Pt 180°C(red form) or 217°C(grey form)
First isolated in 1818 by Berzelius.
Selenium is not really a metal, being more
akin to sulphur than the other similar element tellurium.
Like sulphur, it exists in a number of allotropic forms, the main ones
being red and grey selenium. The grey form is a good conductor of
electricity when illuminated, thus its use in light sensitive devices.
A medal has been made of this element to
commemorate Berzelius.
No coins in their characteristic shape have
been 'struck' in stone, although very large stones were used as currency
on the island of Yap. These items and other non-metallic items used as a
medium of exchange in primitive cultures are beyond the scope of this
article. If you are interested obtain a copy of 'A Survey of Primitive
Money' by A Hingston Quiggin, published by Methuen in 1949 (also reprinted
with corrections in 1963).
The majority of these metals are either too
reactive, too expensive or just too difficult to work to be used in coins
and medals, although many are useful as alloying additions in industrial
metallurgical applications.
Group One
These elements are known as the alkali
metals. They are all silvery-white in colour, react vigorously with water,
very soft, and react rapidly with air, and are thus totally unsuitable for
coins.
Element (Li), Atomic No. 3, density 0.534
kg/litre, M.Pt 181°C
Softer than lead but harder than sodium or
potassium, lithium is the lightest of all solid elements.
Element (Na), Atomic No. 11, density 0.97
kg/litre, M.Pt 98°C
Element (K), Atomic No. 19, density 0.86
kg/litre, M.Pt 64°C
Potassium catches fire when in contact with
water.
Element (Rb), Atomic No. 37, density 1.53
kg/litre, M.Pt 39°C
Rubidium ignites spontaneously when exposed
to air.
Element (Cs), Atomic No. 55, density 1.87
kg/litre, M.Pt 29°C
Group Two
The first group are known as the alkaline
earth metals.
Element (Be), Atomic No. 4, density 1.85
kg/litre, M.Pt 1277°C
An expensive metal that if burnt creates
very toxic compounds. Need I say more!
Element (Ca), Atomic No. 20, density 1.55
kg/litre, M.Pt 838°C
A reactive and brittle metal, it is stable
in dry air but reacts vigorously with water. Having such a coin in your
hot sticky hand would have unpleasant consequences!
Element (Sr), Atomic No. 38, density 2.54
kg/litre, M.Pt 768°C
A ductile white metal, more reactive than
calcium.
Element (Ba), Atomic No. 56, density 3.5
kg/litre, M.Pt 714°C
Strontium and barium are chemically similar
to calcium.
Element (Cd), Atomic No. 48, density 8.65
kg/litre, M.Pt 321°C
Element (Hg), Atomic No. 80, density 13.55
kg/litre, M.Pt -38.4°C
A liquid at room temperature! Hardly
suitable for coins.
Group Three
Element (B), Atomic No. 5, density 2.34
kg/litre, M.Pt 2030°C
A black opaque element harder than
carborundum. Well known as a neutron absorber used in alloy form for
nuclear reactor control rods.
Element (Sc), Atomic No. 21, density 2.99
kg/litre, M.Pt 1539°C
Element (Y), Atomic No. 39, density 4.47
kg/litre, M.Pt 1509°C
Used in ceramic compounds to make
high-temperature superconductors.
Element (La), Atomic No. 57, density 6.19
kg/litre, M.Pt 920°C
Element (Ga), Atomic No. 31, density 5.91
kg/litre, M.Pt 30°C
As mentioned above, this melts all too
easily. It is also very expensive.
Element (In), Atomic No. 49, density 7.3
kg/litre, M.Pt 156°C
Element (Tl), Atomic No. 81, density 11.85
kg/litre, M.Pt 303°C
Group Four
Element (Ge), Atomic No. 32, density 5.32
kg/litre, M.Pt 937°C
The semi-conductor that was used for the
first transistors.
Group Five
Element (As), Atomic No. 33, density 5.72
kg/litre, Sublimes at 613°C
A highly poisonous element. Three
allotropes exist, but the stable form at room temperature is grey and
metallic in appearance. It is very brittle.
Element (Bi), Atomic No. 83, density 9.80
kg/litre, M.Pt 271°C
Bismuth is a grey-white metal with a pink
tinge. It is very brittle.
All elements with a higher Atomic Number
than bismuth are radioactive.
Group Six
All metals in this group have been used for
coins or medals.
Group Seven
Element (Tc), Atomic No. 43, density 11.46
kg/litre, M.Pt 2130°C
There are no stable isotopes of this
element which is not found in nature. It is a radioactive element, and it
seems that there is a quantity in the Irish Sea at present. It is said to
be the world's most expensive metal.
Group Eight
Element (Ru), Atomic No. 44, density 12.2
kg/litre, M.Pt about 2500°C
Element (Rh), Atomic No. 45, density 12.44
kg/litre, M.Pt 1966°C
Element (Os), Atomic No. 76, density 22.57
kg/litre, M.Pt about 2700°C
Element (Ir), Atomic No. 77, density 22.5
kg/litre, M.Pt 2454°C
These are all scarce platinum group metals.
In addition they are far more difficult to work than either platinum
or palladium, the more common elements of the group,
making production of coins or medals in these metals extremely difficult,
if not impossible. Rhodium and iridium can be cold worked to a limited
extent after hot-working, whereas ruthenium presents greater difficulties
and osmium is virtually unworkable. Osmium and iridium are used in alloy
form for hard-wearing fountain pen nibs.
One or two trial pieces have been struck in
rhodium, but is much more often used as a tarnish resistant coating for
silver. A fantasy piece struck by the firm John Pinches in iridium is
known.
Lanthanides
A whole collection of very similar metals
known as the Rare Earths. A mixture of these called Misch Metal is used
for lighter flints.
For lanthanum see above.
Element (Ce), Atomic No. 58, density 6.77
kg/litre, M.Pt 804°C
This is the most common of the rare earths.
The others are:
Praseodymium (Pr), At.No. 59,
density 6.77 kg/litre, M.Pt 919°C
Neodymium (Nd), At.No. 60, density 7
kg/litre, M.Pt 1019°C
Used in magnetic alloys.
Promethium (Pm), At.No. 61, M.Pt
1027°C
Radioactive, with no stable isotope
Samarium (Sm), At.No. 62, density
7.49 kg/litre, M.Pt 1072°C
Used in magnetic alloys.
Europium (Eu), At.No. 63, density
5.25 kg/litre, M.Pt 826°C
I believe that europium oxide is the
material used in TV's for the red phosphor on the screen.
Gadolinium (Gd), At.No. 64, density
7.86 kg/litre, M.Pt 1312°C
Terbium (Tb), At.No. 65, density
8.25 kg/litre, M.Pt 1356°C
Dysprosium (Dy), At.No. 66, density
8.55 kg/litre, M.Pt 1407°C
Holmium (Ho), At.No. 67, density
8.79 kg/litre, M.Pt 1461°C
Erbium (Er), At.No. 68, density 9.15
kg/litre, M.Pt 1497°C
Thulium (Tm), At.No. 69, density
9.31 kg/litre, M.Pt 1545°C
Ytterbium (Yb), At.No. 70, density
6.96 kg/litre, M.Pt 824°C
Lutetium (Lu), At.No. 71, density
9.85 kg/litre, M.Pt 1652°C
Actinides
Element (Th), Atomic No. 90, density 11.66
kg/litre, M.Pt 1750°C
Element (U), Atomic No. 92, density 19.07
kg/litre, M.Pt 1132°C
Uranium and thorium are both weakly
radioactive, with such long half-lives that they are found in reasonable
quantities in nature. The remaining actinides are all radio-active. The
activity of uranium is so low that it could be handled with minor
precautions, but it would be unwise to make coins out of it!
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