General and Technical details on Platinum
Why Platinum is so special
All gems and jewels have three attributes in common- They are Beautiful, Durable and Rare.
Platinum has all these and more:-
• Is compatible with all skin types
• Produces no allergic reactions
• It is inert
• It does not discolour or tarnish
• Is extremely resistant to wear
• Is ideal for use with precious stones, providing a secure and firm setting because of its high resistance to heat and other influences
• Is naturally white
• Is extremely dense, gives a very satisfying heavy feel
• It is the most noble of all the precious metals
• It is rare
Platinum jewellery is non-allergenic, compatible with all skin types. It is the only material suitable for the electrodes in heart pacemakers
Platinum is an inert element which is extremely robust and stable and exceptionally resistant to corrosion. It is one of the few metals unaffected by atmospheric exposure, even in a sulphur polluted industrial environment. It retains its polish and lustre up to its melting point.
It is very wear resistant which means it will not wear out fast. A piece of jewellery with fine patterns or fine filigree work will not wear out fast. Wedding rings made in the 1930`s with engraved designs, still have their designs clearly showing. In gold, these designs were worn off a long time ago. Platinum is ten times harder to work that Gold.
Because of its high tensile strength in very thin sections, platinum is perfect for the setting of diamonds and fine stones. Its whiteness allows more light to reflect in and out and show the true colour of the stones. Its strength holds them securely with the minimum ‘setting’ covering the stone.
What is Platinum
Using today’s modern techniques it takes 5 months to extract one troy ounce (31.1gms) from ten tonnes of ore, for gold it is only 4-5 weeks.
It was not until the mid-eighteenth century that scientists and alchemists began to solve the problem of producing this metal in its pure form. Platinum formed such a strong natural alloy with its sister group metals, that solutions of each metal had to be eliminated before pure platinum could be obtained. The other metals are rhodium, ruthenium, osmium, palladium and iridium.
No other metal has the same properties of Platinum.
It has an extremely high Melting point.
It is very hard and durable.
Its purity is almost entirely unaffected by corrosive substances. It is a natural Catalyst.
It does not oxidise, discolour or tarnish
In short platinum is virtually indestructible.
What is the difference between Platinum and White gold?
Platinum is an element in its own right and is a pure metal. It is alloyed with other metals to improve its working qualities, for example to make it harder, more malleable and to enable multiple soldering. It is naturally white and does not need plating with another metal for ‘show’.
White gold is a man-made, made-up metal, as gold is naturally yellow. 18ct. gold is an alloy of 75% gold and 25% is other metals. The White metals used for the 25% can be nickel, silver, manganese or palladium. As a result of these alloys, white gold it is not always suitable for body jewellery. Very often the raw colour is greyish gun metal with a slight yellow tinge. To make it totally white it is then plated with another metal (usually rhodium) to give it a white look. This plating will wear off in time.
How Platinum compares with other metals
Platinum 95% Gold 75% Silver 92.5% Steel
Carat 950 18ct.(yellow) Sterling
Chemical Symbol Pt Au Ag Fe
Density 20.6 15.5 10.5 7.7
Melting point 1750 900 890 1450
Its vital statistics
Chemical Symbol Pt
Density (g / cubic cm) 21.45
Melting point (degrees C) 1769
Vickers Hardness no. * 41
Electrical resistivity 9.85
(microhm.cm at 0 degree C)
Thermal Conductivity 73
(watts /metre/degree C)
Tensile strength * 14
(kg/square mm)
figures for pure Pt.
* = annealed condition
As refined platinum it first appears as grey, dusty granules. These are melted into ingots of various sizes. In the UK and Europe the main quality or carat of platinum is 950 parts per 1000 it is alloyed to give greater flexibility in working conditions. By alloying it with different metals, different qualities are given to the alloy. To make an easily worked copper is used and when an item is going to be made by casting then cobalt is often used. It must be remembered that only 5% is added to the alloy and so it has no effect on the general qualities of Platinum. The other metals themselves are not reactive.
About the other Platinum sister metals
Palladium Rhodium Iridium Ruthenium Osmium
Chemical Symbol Pd Rh Ir Ru Os
Density 12.02 12.41 22.65 12.45 22.61
Melting point(deg.C) 1554 1960 2443 2310 3050
Vickers Hardness 41 101 220 240 350
Electrical resisivity 9.93 4.33 4.71 6.8 8.12
Thermal conductivity 76 150 148 105 87
Tensile strength 17 71 112 165 ---
Most metals are used in industry in alloys and catalysts. Rhodium is used in jewellery for plating, often to cover up bad coloured white gold. Platinum is used in a very powerful anti-cancer drug.
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Working with Platinum- Technical details
We have been making platinum jewellery in all shapes and sizes since 1982 and have noted how platinum behaves when worked. Here are some qualities and characteristics that we have noted.
Platinum is a very different metal from gold and silver; its qualities are as useful as they are a hindrance. It is very predictable and works well if care is taken but is very unforgiving if treated the wrong way.
As silver is different to gold so platinum is different from both of these. It is a very contradictory metal as it gives and takes at the same time. Your experience may be different; in making jewellery there is often many ways of doing a job and experiencing the metal from different angles.
Be aware of it qualities
Poor heat conductivity
Never oxidises or tarnishes
Very wear resistant
Heavy (dense)
It absorbs carbon when heated
It has many anomalies
Although it is hard work to file and polish - it will scratch and mark very easily.
Although a bad heat conductor - it will “grab” heat very quickly. Be careful when soldering platinum to gold, put heat on the gold not platinum.
It is a back to front metal
Be sure of what you are going to do before you start.
Because of its inability to oxidise, units can be prepared and polished before assembly.
You can finish before you start.
Always work clean
Make sure all your tools are clean from contaminates. Clean your files if used for other metals. It will take up surface contaminates very easily at low heat from other metals.
Never use lead solder
Polish the surfaces of your pliers, ensuring marks or indents are not put onto metal. Use soft jaw pliers and tungsten steel polished drawplates if possible.
Do not mark metal unnecessarily as it is very hard to clean up afterwards and polish.
Although it work hardens, it is always malleable.
When bent it has a “dead action” and does not have a spring back. It is ideal for settings.
When stretched or bent
It I will often have a crinkled effect or “orange peel “ look to the surface.
It is gritty to machine work
General working metal is sticky and “judders” giving an uneven surface i.e. when diamond milling, thread cutting. It is best to keep one set of files exclusively for platinum as they will be blunted for gold work, but they will work fine for platinum.
Never anneal or work on a carbon charcoal block
Platinum will absorb carbon from the charcoal block and make it brittle- us porcelain or a special platinum soldering block.
Use Tungsten steel tweezers when holding a platinum piece to heat
Normal carbon steel jewellery tweezers will affect the metal. Platinum will absorb carbon from the carbon steel when heated, giving it a dark stain and make it brittle.
It has low heat conductivity
When annealing and heating platinum do it long and slow as it takes time for the heat to travel through the metal. The main advantage of this is when soldering - it will only affect a small area rather than the whole item. The converse is also true for cooling down. It needs more time to cool, when quenching there is still heat in it after the first hiss.
When soldering, make sure there is mechanical strength in the join
Platinum does not have a fused join but more of a “glue” surface joint. The solder can “peel” off the surface.
When sizing a ring by stretching, the solder joint can easily break. Hard solder and welding is better for this.
Use as hard or high temp solder possible. Most Platinum solders either have low or non quantity of platinum in them.
Soldering
Easy solder has a high silver content and so may oxidise, flux may be needed
For joints that must not be seen (as in ring shanks) use welding or 1700 solder. Easy solder joints may blacken in time. See notes on polishing.
Use as hard or high temp solder possible. Most solders either have low or non-quantity of platinum in them.
Soldering a joint
The faces must meet exactly as you cant “fill” a crack and it reduces strength.
Polishing-There are no short cuts
In polishing the item, it has to be emeried through many grades. All marks and scratches must be removed from the previous coarser grade abrasive.
It is not like gold or silver where marks can be polished marks out using the polishing mop.
Polishing is a grinding process
Take all marks out using 1000 grade emery paper. For very fine polish then use crocus paper. Followed by “Brushing compound” on a coarse calico mop. Then follow with “white compound”(as used for stainless steel) on a firm bound calico mop. Use a soft flowing motion as though it were a grinding wheel. The surface of the metal is being ground down by the compound, not moved as is in silver and gold. The use of water on the mop will help keep the temperature down and help with the polish. Care must be taken not to overwork a piece as solder can be dragged from the joint. The solder is often softer than the metal being polished. It burnishes very well.
If polished properly, it does not need Rhodium plating
It has a natural colour- Black
Its colour is like steel. There are different tones for each alloy. Some very low grade American Platinum is pink. When displaying it, put it onto a light colour background, as it will get lost on a dark one. This is due to its molecular structure and low reflectivity. Ruthenium alloy is whiter but gives a harder harder metal to work. Copper alloy is a good general purpose one is very malleable but is greyer in colour.
Cobalt alloy is mildly magnetic
Used in casting alloys and some chain wire.
Some platinum will blacken when heated
High copper and palladium content -often used in sheet used for stampings. If it is a palladium alloy passing or “wafting” a soft gassy(yellow tip) flame over the piece can remove the blue or blackness.
Designs and pieces are often finer and on a smaller scale and size
Its high value and density may justify the use of more hand work, due to its weight, high price and working qualities.
Vital statistics
Approx twice weight of silver and 9ct (densities Pt950=20.5, 18ct=15.4, 9ct=11.2, silver925=10.3)
35% heavier than 18ct Gold
Melts at 1769 C (pure), 1745-1765 C (general 950/1000)
According to World Gold Council it is 10 times harder to work that gold(!?)
20 times rarer than Gold
Takes approx 5 months to refine (gold takes 4 weeks)
Takes approx 10 tons of ore to produce 1 ounce of platinum
The price is set by its rarity, there is usually a greater demand than supply.
It has been considered on of the 21st century wonder metals. There are still many unknown secrets and uses to be discovered.
Rider and Rider
Steve Rider FGA
July 2003
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