Precious Metal, Platinum, Rhodium, Palladium, Gold

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Precious Metals...Platinum, Rhodium, Palladium,

There are more precious metals used in Jewellery than Silver and Gold, precious meaning expensive. They are mainly Platinum, Palladium and Rhodium. I include the others just for the sake of completeness. This is a short guide to these metals, giving you an idea of some their properties, relative relationships and uses.
All these metals have many industrial uses, some vital, and not just decorative.
As most of you are familiar with gold, I will use gold as a standard that describes their relative properties.
The values stated will vary somewhat with supply and demand fluctuations, sometimes extremely, but it should give you a RELATIVE idea in relation to gold. You can always get a current price on the net if needs be.

  • GOLD (Au)
  • Atomic Number: 79
    Density: 19.32 g/cm3....about 19 times heavier than water
    Melting point: 1064°C
    Mohs hardness: 2.5...soft
    Value: See the daily news.
    I will presume everyone is familiar with its uses and alloys as this is really about other precious metals.
    OTHER USES: Used in electronics, dental crowns and coins. Gold, the metal chosen for the supposed financial security it can provide.

  • SILVER (Ag)
  • Atomic Number: 47
    Density:10.5 g/cm3....about 1/2 the weight of gold.
    Melting point: 961°C
    Mohs hardness: 2.5...soft
    Value in terms of gold: About 1/50th - 1/90th of gold. Historically it it used to be about 1/10th - 1/15th. So relatively inexpensive
    I will presume everyone is familiar with its uses and alloys.
    OTHER USES: In many many chemical compounds, photographic film and paper electronics, mirrors and batteries.

  • Atomic Number: 78
    Density: 21.37 g/cm3...a bit heavier than gold
    Melting point: 1772°C
    Mohs hardness: 3.5
    Value in terms of gold: About 1 1/2 to 2 1/2 of gold. Substantially more expensive than gold.
    A FEW OBSERVATIONS ABOUT PLATINUM...Platinum became popular during the Art Deco period as a Jewellers metal and has been used up to the present. With its high melting point and hardness it is a difficult metal to work so generally it was used on "one off" high quality hand made pieces. White metal is particularly important in diamond settings as it does not make your white diamond look off colour as a yellow gold setting might. The joy of old platinum jewellery is that it is usually in very good condition, being so hard. If you look at an old Art Deco ring made of a platinum setting and gold band, the gold band may have considerable wear but the setting is usually in very good condition. Jewellers may dislike working with it because of its characteristics but collectors of old jewellery love it. Also excellent for making the claws that hold gemstones. A most secure metal.
    OTHER USES: To make crucibles, special containers, as a catalyst, in dental crowns, as an anti-tumour agent and to make standard weights and measures. It is also combined with cobalt to produce very strong magnets.

  • RHODIUM (Rh)
  • Atomic Number: 45
    Density: 12.44 g/cm3...Relatively light
    Melting point: 1966°C
    Mohs hardness: 6
    Value in terms of gold: 4 to 5 times of gold.
    A FEW OBSERVATIONS ABOUT RHODIUM...Horrendously expensive, hard, a high melting point and extremely chemically inactive, almost untarnishable. Widely used to plate white gold or silver to give it a durable and bright mirror like finish. This is a most common practice and is NOT indicated with jewellery hallmarks. Rhodium plating is also used around diamond settings to make white diamonds look whiter. If you find your white gold ring has lost it's shine and sparkle, has a yellowish tinge, it is a fairly simple matter for a jeweller to have it replated with rhodium to bring back its original mirror finish. It is brittle, difficult to work mechanically and too expensive to use in other forms for jewellery manufacture.
    OTHER USES: Used as a coating to prevent wear on high quality science equipment and with platinum to make thermocouples. Also used in headlight reflectors, telephone relays and airplane spark plugs.

  • Atomic Number: 46
    Density: 12.16 g/cm3...Relatively light
    Melting point: 1552°C
    Mohs hardness: 4.75
    Value in terms of gold: 1/3 to 1/2 of gold
    A FEW OBSERVATIONS ABOUT PALLADIUM...A hard white metal used in jewellery for settings, etc. Excellent hardness and working characteristics and relative cost make this an excellent white metal for jewellery manufacture. It makes very strong claws and settings that hold precious gems and keeps white diamonds looking white. Mixed with yellow gold to make white gold.
    OTHER USES: Used in alloys for telecommunication equipment switching systems and electrical relays, catalyst for reforming cracked petroleum fractions, metallizing ceramics, aircraft sparkplugs.

  • OSMIUM (Os)
  • Atomic Number: 76
    Density: 22.59 g/cm3...a bit heavier than gold
    Melting point: 3027°C...Extremely high
    Mohs hardness: 7...Super hard
    Value in terms of gold: About 1/2 of gold.
    A FEW OBSERVATIONS ABOUT OSMIUM...Oxides reasonably easily. Used as an alloy with other precious metals to increase hardness. See Iridium.
    OTHER USES: Instrument pivots (such as compass needles and clock bearings), to make electric light filaments. Used for high temperature alloys and pressure bearings.

  • IRIDIUM (Ir)
  • Atomic Number: 77
    Density: 22.56 g/cm3
    Melting point: 2443°C
    Mohs hardness: 6.5...Very Hard
    Value in terms of gold: About 1/2 of gold.
    A FEW OBSERVATIONS ABOUT IRIDIUM...The most inert precious metal. Used in alloys with other precious metals. An Osmium + Iridium (Osmiridium) and Ruthenium alloy is used to make super hard pen nib tips.
    OTHER USES: To make crucible and special containers. Used to make alloys used for standard weights and measures, and heat-resistant alloys. Also used in cancer irradiation, hypodermic needles, helicopter spark plugs and as hardening agent for platinum

  • Atomic Number: 44
    Density: 12.06 g/cm3...Relatively light
    Melting point: 2250°C
    Mohs hardness: 6.5...Very hard
    Value in terms of gold: A bit more than 1/2 of gold.
    Not used much in jewellery.
    OTHER USES: Used to harden platinum and palladium. Also used in eye treatments, thickness meters for egg shells, fountain pen points, and electrical contacts. Aircraft magnetos use platinum alloy with 10% ruthenium.

  • RHENIUM (Re)
  • Atomic Number: 75
    Density: 21.04g/cm3...Relatively light
    Melting point: 3180°C...The highest.
    Mohs hardness: 7...Super hard. Diamond has a hardness of 10
    Value in terms of gold: A bit more than 1/2 of gold.
    A FEW OBSERVATIONS ABOUT RHENIUM...It was the last naturally occurring stable element to be discovered. Not used in jewellery but you need about 35 kilos to make a commercial jet engine at around $12,000 a kilo.
    OTHER USES: It is added to tungsten and molybdenum alloys and is used in refractory metal components of missiles, electronic filaments, electrical contacts, high-temperature thermocouples, oven filaments, electrodes and igniters for flash bulbs.

    LASTLY, I point out that I am not a jeweller and that the above guide is just that, a guide.
    I am a pawnbroker with 25 years experience. If you want professional advice go to a jeweller.
    Vote as appropriate.
    © 2010 Edward Vabolis

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