Precious Metal, Platinum, Rhodium, Palladium, Gold

Precious Metals...Platinum, Rhodium, Palladium, Gold....propertiesThere are more precious metals used in Jewellery than Silver andGold, precious meaning expensive. They are mainly Platinum, Palladiumand 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 theirproperties, 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 demandfluctuations, sometimes extremely, but it should give you a RELATIVEidea in relation to gold. You can always get a current price on the netif needs be.GOLD (Au)Atomic Number: 79Density: 19.32 g/cm3....about 19 times heavier than waterMelting point: 1064CMohs hardness: 2.5...softValue: 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, themetal chosen for the supposed financial security it can provide.SILVER (Ag)Atomic Number: 47Density:10.5 g/cm3....about 1/2 the weight of gold.Melting point: 961CMohs hardness: 2.5...softValue in terms of gold: About 1/50th - 1/90th of gold. Historicallyit it used to be about 1/10th - 1/15th. So relatively inexpensiveI 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.PLATINUM (Pt)Atomic Number: 78Density: 21.37 g/cm3...a bit heavier than goldMelting point: 1772CMohs hardness: 3.5Value 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 duringthe Art Deco period as a Jewellers metal and has been used up to thepresent. With its high melting point and hardness it is a difficultmetal to work so generally it was used on "one off" high quality handmade pieces. White metal is particularly important in diamond settingsas it does not make your white diamond look off colour as a yellow goldsetting might. The joy of old platinum jewellery is that it is usuallyin very good condition, being so hard. If you look at an old Art Decoring made of a platinum setting and gold band, the gold band may haveconsiderable wear but the setting is usually in very good condition.Jewellers may dislike working with it because of its characteristicsbut collectors of old jewellery love it. Also excellent for making theclaws 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 weightsand measures. It is also combined with cobalt to produce very strongmagnets.RHODIUM (Rh)Atomic Number: 45Density: 12.44 g/cm3...Relatively lightMelting point: 1966CMohs hardness: 6Value in terms of gold: 4 to 5 times of gold.A FEW OBSERVATIONS ABOUT RHODIUM...Horrendously expensive, hard, ahigh melting point and extremely chemically inactive, almostuntarnishable. Widely used to plate white gold or silver to give it adurable and bright mirror like finish. This is a most common practiceand is NOT indicated with jewellery hallmarks. Rhodium plating is alsoused around diamond settings to make white diamonds look whiter. If youfind your white gold ring has lost it's shine and sparkle, has ayellowish tinge, it is a fairly simple matter for a jeweller to have itreplated with rhodium to bring back its original mirror finish. It isbrittle, difficult to work mechanically and too expensive to use inother forms for jewellery manufacture.OTHER USES: Used as a coating to prevent wear on high qualityscience equipment and with platinum to make thermocouples. Also used inheadlight reflectors, telephone relays and airplane spark plugs.PALLADIUM (Pd)Atomic Number: 46Density: 12.16 g/cm3...Relatively lightMelting point: 1552CMohs hardness: 4.75Value in terms of gold: 1/3 to 1/2 of goldA FEW OBSERVATIONS ABOUT PALLADIUM...A hard white metal used injewellery for settings, etc. Excellent hardness and workingcharacteristics and relative cost make this an excellent white metalfor jewellery manufacture. It makes very strong claws and settings thathold precious gems and keeps white diamonds looking white. Mixed withyellow gold to make white gold.OTHER USES: Used in alloys for telecommunication equipmentswitching systems and electrical relays, catalyst for reforming crackedpetroleum fractions, metallizing ceramics, aircraft sparkplugs.OSMIUM (Os)Atomic Number: 76Density: 22.59 g/cm3...a bit heavier than goldMelting point: 3027C...Extremely highMohs hardness: 7...Super hardValue in terms of gold: About 1/2 of gold.A FEW OBSERVATIONS ABOUT OSMIUM...Oxides reasonably easily. Used asan alloy with other precious metals to increase hardness. See Iridium.OTHER USES: Instrument pivots (such as compass needles and clockbearings), to make electric light filaments. Used for high temperaturealloys and pressure bearings.IRIDIUM (Ir)Atomic Number: 77Density: 22.56 g/cm3Melting point: 2443CMohs hardness: 6.5...Very HardValue 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 nibtips.OTHER USES: To make crucible and special containers. Used to makealloys used for standard weights and measures, and heat-resistantalloys. Also used in cancer irradiation, hypodermic needles, helicopterspark plugs and as hardening agent for platinumRUTHENIUM (Ru)Atomic Number: 44Density: 12.06 g/cm3...Relatively lightMelting point: 2250CMohs hardness: 6.5...Very hardValue 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 eyetreatments, thickness meters for egg shells, fountain pen points, andelectrical contacts. Aircraft magnetos use platinum alloy with 10%ruthenium.RHENIUM (Re)Atomic Number: 75Density: 21.04g/cm3...Relatively lightMelting point: 3180C...The highest.Mohs hardness: 7...Super hard. Diamond has a hardness of 10Value in terms of gold: A bit more than 1/2 of gold.A FEW OBSERVATIONS ABOUT RHENIUM...It was the last naturallyoccurring stable element to be discovered. Not used in jewellery butyou 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 isused 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. SEE MY OTHER GUIDES FOR OTHER INFORMATION ON JEWELLERY.Vote as appropriate. 2010 Edward Vabolis