The History of Platinum
Platinum is a white metallic element and the most important member of the platinum group metals (iridium, palladium, platinum, rhodium, ruthenium and osmium). It was not until the late 1500s that Spanish explorers of Colombia discovered the metal. They named it "platina", meaning "silver of little value", because they did not know what to do with it. Specimens of the metal were not taken to Europe until the 1700s. Since then, the other five metals in the platinum group have been discovered. The six metals are generally found together in nature.

These metals have several characteristics in common: a silvery-white color, rarity, unusual resistance to chemical corrosion, high melting points, and certain chemical peculiarities, such as the formation of complex salts useful in electroplating and photography.  The platinum group metals along with gold and silver comprise the "noble," or "precious" metals.

The Platinum Market
In 1920, 65% of the platinum used in America went into jewelry. By 1972 that figure was down to 2%. Industrial demand had priced the metal out of the jewelry market. With the soaring cost of gold in the late 1970s, platinum began to regain its lost glory as the metal of choice for diamond jewelry. As of 1994, of the 4,320,000 ounces in demand worldwide, 1,700,000 (approximately 40%) was used for jewelry.

Jewelry is the largest single application of platinum, due almost entirely to the large Japanese market. In 1994, 1.5 million ounces went to the Japanese jewelry trade. On a per capita basis, the Japanese people use at least 50 times the platinum for jewelry than does the United States.

In 1994, 4,320,000 ounces of platinum were mined. That equates to an area 6' long x 6' x wide x 6' high. That's it. Compare this to 74,100,000 ounces of fine gold (18' x 18' x 13') that was mined in 1994, which is 19 ½ times as much as mined platinum. Platinum is truly a rare metal.

Characteristics of Platinum
Working with platinum is more different than it is difficult. With respect to melting, annealing and casting, these differences are very pronounced. You must not transfer what you know about gold and use it on platinum.  With respect to rolling, bending, drawing, and workability, platinum has many positive characteristics.

Like gold, platinum must be alloyed with other metals to make it suitable for jewelry use. The most popular alloys for jewelry are 90% platinum/10% iridium and 95% platinum/5% ruthenium. These two alloys are very similar in working characteristics. Certain characteristics of platinum need to be taken into account when designing and working on a piece of jewelry. Platinum is a very dense metal, one of the heaviest on the periodic table.

If the same piece is made in silver and in platinum, the platinum piece will weigh twice as much. What this also means is that much thinner gauges of platinum can be used to achieve the same weight of other precious metals. Platinum is also very strong, thus structural integrity and rigidity will be maintained while using thinner material.

Melting Platinum
The high melting point and poor thermal conductivity make platinum more difficult to melt than gold or silver. A torch capable of melting metal at 1927oC or 3500oF is required. The recommended gases to use are natural gas/oxygen or hydrogen/oxygen. Unlike gold, melt the platinum as quickly as possible by using a hot oxidizing flame.  Fast melting helps prevent long exposure of the eyes to the bright light.

An alumina/fused silica melting crucible must be used, because of the high temperature required to melt platinum. Use clean crucibles that are designated for platinum only. Platinum is easily contaminated. It is very important to keep your work area clean, in order to avoid mixing any other metals with platinum.

Platinum can be hammered and formed into plate or rod. Because of this, platinum can be melted in a crucible and left to solidify into a button shape. This is important because of platinum's low heat conductivity. The metal quickly solidifies once the torch is taken away, which makes it very difficult to pour molten platinum into a mold.

Steps to Successfully Melt Platinum
For safety when melting platinum, use welding equipment. Prior to heating, prepare the platinum by pickling for at least 15 minutes in a mild nitric acid or bi-sodium sulfate solution. This will eliminate any cross-contamination from residual materials.

The torch should be 12" to 18" long to keep hands and body a safe distance from the heat. Melt the platinum using the force of flame to stir the metal. Make sure that the platinum is completely molten. Pull away the torch and the platinum will begin to solidify. When the metal loses its bright white color and turns to a dark red it may be quenched. Pick up the crucible with wraparound tongs, as the crucibles are brittle and can crack or chip easily if not handled properly. You want to quench the button while it is warm so it releases from the crucible.

Take the crucible out of the water and flip the button over. You will notice moonlike craters in the surface of the metal. Grind and hard buff the silica stuck to the bottom of the metal thoroughly. Place the platinum on a piece of ATJ grade graphite. Make sure the graphite plate is not sitting on a surface susceptible to burning.

Take the torch and heat the platinum until the surface becomes molten. Do this to eliminate the surface pits and to push any silica left from the crucible to the edges of the button. Make sure that you thoroughly flow the top of the button. There is usually a large sinkhole in the center of the button, below the surface. Use a back and forth motion with the flame until all air bubble holes are filled. Once the surface of the button is smooth, take away the flame. Work quickly while the metal is still hot.

Move the button with a pair of tongs either to a drop hammer or a steel plate so that the button can be hammered. At this point the button can be hammered flat for sheet or into a rectangle to make wire. Never fold the metal over completely as this will cause cracks. Flow the metal with the torch flame after hammering.

Rolling
After hammering, the platinum can be rolled down into sheet or drawn into wire.  Platinum is very malleable and can be reduced, without annealing, further than karat gold. Platinum can easily be reduced at least 50% in thickness before an additional anneal is necessary.

Rolling platinum can be done very easily with little stress to your rolling mill. If you begin with a thickness of .150" you can roll to .030" without annealing. The metal will roll out easily, but will be hardened enough in the process to get nice, sharp pieces without blanking. However, if the metal is going to be worked after rolling, anneal at .050" before rolling to .030". 

Annealing can be done using a handheld torch. Again, I recommend oxygen/natural gas. Make sure that the metal is clean. Use only a brick designated for platinum annealing. Although platinum has a high melting point, it can be over-annealed. Too frequent annealing or annealing the metal for too long can cause grain growth. The larger grain size and the voids between the grains make the surface of the metal look pitted, textured or frosted, making it difficult to achieve a high polish. This will affect the metal during forming and polishing operations.

Use a bright blue oxidizing flame in order to properly anneal the platinum. Softening occurs rapidly at 1000oC or 1800oF, or when the metal is bright orange in color. The trick to annealing is reaching the proper temperature; the most common fault is that you will not heat the metal hot enough to soften it. Once the temperature is reached, annealing will occur rapidly. An average ring will require heating for approximately 30 seconds. A good guide is 1" square by 18 gauge sheet will require 60 seconds. Increase or decrease the time according to the size of the piece. Platinum can be air cooled or quenched in water after annealing.

Brazing and Welding
Platinum can be brazed with a choice of platinum brazing filler material or can be welded with pure platinum. When brazing with the lower temperature platinum filler material you give up color match. When using the lower degree platinum filler materials, you are really using a high gold content filler material. Flux is needed for the 1000o to 1500oC platinum filler material. Flux is not necessary for higher-melting filler materials. However, flux can be used to hold the piece of filler material in place.

Steps for Successful Platinum Brazing
First, a jeweler must make sure that the joint fits tightly. Time and care must be taken to ensure a close fit prior to brazing. The two pieces must be touching each other.  Platinum filler material does not fill gaps.

The second key to successful brazing of platinum is proper heating of the joint. Unlike gold brazing, use a hot flame directly on the platinum joint and filler material. Remember, platinum is a poor heat conductor, so the joint and filler material must be heated directly.  When brazing small joints, hold the entire piece in the air with a pair of cross-lock tweezers. This will allow you to put heat directly on the joint. A water torch works well for platinum filler materials under 1500oC because they have a small, hot flame. If you must set the piece on a flat surface, use a charcoal block. Heat the joint quickly. One of the biggest problems you will encounter is having "cold-brazed-joints". This occurs because of platinum's high melting point and poor heat conductivity. The filler material will flow into the joint. However, the platinum is not hot enough to cause fusion. Once the piece of jewelry is hammered, the joint will break. Poor heat conductivity does have its advantages. You can use this in a positive way, especially when multiple brazing is necessary. When doing fine work requiring multiple brazed joints, you can braze in close proximity by using progressively lower-melting filler materials.

A ring can be sized, even if it is set with stones, by using a fine-tip torch. This can be done because platinum has a high resistance to heat. Therefore, the flame can be concentrated in a small area without damaging the rest of the ring. Direct the flame away from any stones to further minimize damage.  If done properly, even with platinum's high melting point, you can weld a ring shank together without damaging the stone.  (As a side note, when finishing, platinum is more difficult to polish than gold, because of its hardness and increased density. It is recommended that whenever possible, parts should be pre-polished before assembly. This will save a lot of extra labor at the end of the job. Platinum will not oxidize during brazing, so the piece will maintain its polish if done beforehand.)

Welding
In a platinum application, welding is different from brazing because platinum is joined together by heating the metal until it is fused together. As a guideline, you should weld when sizing a ring and braze when attaching components to platinum. When joining gold to platinum, always use a filler material that matches color and melting temperatures of the metal with the lower melting point, which is 18Kt gold in this case. Welding is possible with pure metals, including platinum. This technique takes a little extra skill but gives the most invisible joint. Pure platinum melts 25 degrees lower than platinum/iridium, which is why pure platinum is used instead of the platinum/iridium alloy. However, I recommend a 1700oC platinum filler material, which has a better color match than pure platinum. The 1700oC filler material has palladium in it, which gives it a very close color match to a platinum/iridium alloy. Use tension to hold the snippet between the two sides of the joint. Flux may be used to adhere the chip to the joint. Heat the snippet and the joint directly and intensely until the metal flows. This will form an invisible joint of solid metal.

Conclusion
When melting platinum, using the right tools is important. If the wrong torch, gas, crucible, or the wrong platinum scrap is used, a jeweler will already be setting himself up for failure.

When annealing platinum, a jeweler must bring the metal to a high enough temperature, or nothing will occur. The metal must reach a bright orange color to soften the platinum.

Brazing can be successfully achieved if a jeweler remembers: 1) The joint must fit tightly—take the time to make sure it fits perfectly before attempting to braze; and 2) the joint must be heated directly with enough heat to cause fusion.

Platinum has come a long way since its discovery 400 years ago. It is no longer considered "silver of little value". The fact is that platinum has climbed to the top of the noble metals list. Usually only the finest quality jewelry is made from platinum. Today it is more popular than ever. Jewelers and goldsmiths have traditionally shied away from platinum because of its different characteristics.  Unfortunately, until recently, detailed information on working with platinum was rare.  In the past a jeweler could expect to find his written information dated 1800s or earlier. But all of that is changing. Platinum is the white noble metal that is fighting its way back into consumers' hearts—and into their wallets. Don't be left out by not offering it as the premier choice in jewelry for your customer.

V1N3

Platinum Mill Products and Brazing
Torrance D. Hoover
Hoover & Strong

This is an abbreviated version of the original work. For full technical details, please consult the original paper.