Platinum was discovered by early Spanish explorers in Columbia and finally brought back to Europe in 1735. When Platinum was first discovered, people did not know what to do with it so they called it Platina meaning Silver of little value. The native people of Columbia were long aware of Platinum often finding the grayish white heavy nuggets when panning for gold in streams and rivers. The native people would throw the Platinum nuggets back into the stream thinking it was gold that wasn’t ripe yet. Over the years as refining and melting processes were developed, many uses were found for this most valuable metal. Platinum is used in chemical processes as a catalyst, in electrical and electronic applications, in dental applications, medical applications as a cancer treatment and in the finest quality jewelry.
Pure Platinum is a tin white metal, malleable, ductile and harder than silver; it does not tarnish in air or dissolve in any single acid. Platinum ranks 57th in abundance among the elements in the earth’s crust. The metal occurs native in a fairly pure state or alloyed with other metals and nuggets weighing up to 21 pounds have been found. Most of the Platinum used today comes from South Africa or Russia. Pure Platinum has a melting point of 3224 degrees F. / 1773 degrees C., the specific gravity is 21.45 g/cu cm @ 20 degrees C. Over the past 5 years the popularity of jewelry made of Platinum alloys has increased dramatically and many jewelry manufacturers are now making Platinum jewelry to satisfy the demand. Worldwide demand for Platinum is a record 5.35 million troy ounces in 1999 according to Johnson Matthey’s " Platinum 1999" report.
Pure Platinum is much too soft for most jewelry applications and small additions of other platinum group or base metals are added to increase the hardness. A 90% Platinum / 10% Iridium alloy is the most popular alloy for jewelry manufacturing in the United States. The 90% Platinum / 10% Iridium gives an excellent white color with a good hardness and is used for sheet stock, wire goods and investment casting. In recent years a 95% Platinum / 5% Cobalt alloy which is very popular in Europe is gaining in popularity in the United States as a casting alloy. The 95% Platinum / 5% Cobalt is slightly magnetic and has excellent fluidity for filling intricate castings providing a good final hardness. A 95% Platinum / 5% Ruthenium alloy has a fine grain structure, excellent hardness and high tensile strength making it ideal for making tubing and other wrought products where good machining characteristics are required. The 95% Platinum / 5% Ruthenium alloy is not recommended for investment casting due to Ruthenium’s affinity for oxygen that can cause porosity in castings. A new heat treatable Platinum alloy has come on the market consisting of 95.5% Platinum / 3.0% Gallium / 1.5% Indium. This alloy can be investment cast or made into wrought products where a hardening heat treatment can be used to increase the hardness, making it ideal for thin parts that need a springy hardness. Various other Platinum alloys are used in other parts of the world, in Japan, Platinum / Palladium or Platinum / Palladium / Cobalt alloys are used and in Europe, Platinum / Copper or Platinum / Copper / Cobalt alloys are used.
Platinum Jewelry Manufacturing
For those manufacturers accustomed to casting, rolling or finishing gold and silver alloys, working with Platinum seems difficult or alien. Platinum is different to work with than gold and silver alloys but once the processes are understood, it is not so difficult. The biggest difference is in the melting points, a 14 Karat yellow gold alloy has a melting point of 879 degrees C / 1615 degrees F, the melting point of 90% Platinum / 10% Iridium is 1788 degrees C / 3250 degrees F. A calcium sulfate bonded investment is used for gold and silver casting, with Platinum a phosphate bonded or acid bonded investment is required. Higher temperature wax burn-outs and flask temperatures are needed for Platinum casting. Different polishing techniques and compounds are used for finishing Platinum than those used for gold and silver alloys.
Investment Casting Platinum Alloys
Platinum alloys can be melted and cast in specially designed high or medium frequency induction casting machines or torch melted and cast in vertical or horizontal centrifugal casting machines. The induction powered casting machines are very expensive and are usually used by high volume manufacturers. Most of the small and medium sized shops use torch melting and centrifugal casting. The vertical centrifugal casting machine is the most popular for torch melting platinum alloys. The crucibles used are specially formulated for platinum casting such as Wesgo crucibles, check with your supply house for platinum crucibles. Do not use carbon or graphite crucibles for melting platinum. The best gas mix to use for melting platinum is Hydrogen and Oxygen, this mix will melt the platinum alloy quickly. Other gasses can be used such as Propane / Oxygen or Natural Gas / Oxygen but will take longer to melt platinum alloys with. Avoid using Acetylene / Oxygen gas mix on platinum alloys due to carbon contamination. Torches used for melting platinum alloys usually have multiport or rosebud screw on tips and a built in flashback arrestor for safety. Proper eye protection must be worn when melting platinum alloys, # 10 welding goggles are the minimum protection and # 11 or # 12 will provide the best protection of the eyes from ultraviolet radiation when melting. Inadequate eye protection can cause permanent damage to the eyes. Long sleeved heat resistant gloves and a leather apron are advised when casting platinum alloys.
Investment for Platinum Alloys
Gypsum based jewelry investments can not be used for casting platinum or platinum alloys. There are two types of investment normally used to cast platinum alloys, Phosphate bonded investment and Acid bonded investment. The Phosphate bonded investments are the easiest to use and set up quickly allowing burn out within about 2 hours. A 10 hour burn out cycle is usually done. The as cast surface on castings made with the Phosphate bonded investments are rougher and will require more finishing time. The Acid bonded investments will give a smooth strong mold providing a smooth as cast surface requiring less finishing time. The Acid bonded investments are very unforgiving to make, the manufacturers instructions must be followed religiously through all the steps. Long drying times are needed with the Acid bonded investments and absorbent paper must be used during the 16 to 24 hour drying time. The finest quality castings are made with the Acid bonded investments. Recently, a very innovative manufacturer has incorporated ceramic shell molding technology formerly used to make jet engine turbine blades to an investment process for platinum casting. The resulting platinum alloy castings were excellent dimensionally with a smooth as cast surface. Most investment manufacturers will supply
3 to 5 pound samples of platinum investment for trials and it is suggested that several types be tried to find one that is suitable for your operation.
Burn Out Ovens for Casting Platinum Alloys
Gas fired burn out ovens are strongly recommended for wax burn out with platinum investments. The good air flow and even heating in the gas ovens provides a clean investment flask free of carbon residues from the waxes. There are gas fired burn out ovens specially built for platinum casting with an extra burner and thicker insulation to handle the higher temperatures (1600 to 1700 degrees F) required for platinum investments. Electric ovens can be used in smaller operations but the air flow through the ovens during burn out is rather limited and any retained carbon residues will cause casting problems with platinum alloys. The electric ovens can be modified by adding air holes in the top and bottom to improve the air flow and increasing burn out times to assure a clean burn out. Most of the larger manufacturers of platinum alloy castings use gas fired burn out ovens. Accurate temperature controls are essential on any burn out oven used for platinum casting.
Designs Cast in Platinum Alloys
There will be design limitations on jewelry being cast in platinum alloys. Platinum alloys will solidify very quickly and to avoid potential fill or shrinkage problems, thick to thin to thick variations in designs should be avoided. The more complex designs will need to be cast in sections and assembled after casting. Thin detailed portions need be cast separately using higher metal and flask temperatures than the heavier parts of the casting. Designs that cast easily in karat gold alloys may be impossible to cast in platinum alloys in one piece. There will be size limitations on one piece designs cast in platinum alloys due to the rapid rate of solidification. Avoid sharp inverted V shapes, claws or prongs that are thicker at the tips than at the base, forms that curve back on themselves, deep holes or cavities with small openings, large thin areas or long wire and tube sections in designs being cast in platinum alloys.
Sprue Systems for Platinum Alloy Casting
Due to the rapid solidification rate of platinum alloys, shorter, heavy, straight sprue systems must be used. Multiple heavy sprues may be required on some designs. The sprue size should be equal to or in some cases up to 30% larger than the largest cross section of the casting being fed. The first rule of casting must always be followed, "Always sprue to the heaviest area of the casting", this will help avoid shrinkage porosity and fill problems. Large round sprues flared at the attachment area are ideal for platinum alloy castings and will provide a supply of molten metal to the casting as it solidifies. It may be helpful to use a multiple sprue system to the edges of heavier rings with large amounts of detail on the surface of the design.
Wax Patterns for Platinum Alloy Casting
Use a sturdy, clean burning wax for casting platinum alloys. Some new wax formulations are now available for platinum casting, check with your supply house. Make sure the waxes are clean and free of any talc or mold release residue as this will cause rough surfaces on the finished casting.
Assembly of Waxes on the Wax Base
A dome shaped wax base is normally used to attach the wax patterns to before investing. The tall vertical trees used for gold casting can not be used for platinum casting due to the rapid solidification rate of platinum alloys. When multiple pieces are cast in platinum, short sections of wax sprue rod are attached horizontally to the wax base and the lighter weight castings attached to the wax sprue rod. Heavier castings are usually attached directly to the wax sprue base. The wax used for sprue rods and the wax base should have a lower melting point than the wax patterns used for the castings.
Investing the Wax Assemblies
Once a suitable platinum investment is selected that suits your needs, a complete set of instructions should be obtained from the investment manufacturer or supplier. Follow the instructions to the letter. The platinum investments will be different than the regular jewelry investments.
Each type of platinum investment will have a specific technique for mixing, de-airing, drying and set up time. The acid bonded investments will require absorbent paper to assist the drying of the investment. The metal flasks are normally made of stainless steel or Inconel that will resist the higher heat used in the burn out process for platinum investment. Keep in mind that you will be casting the platinum alloy at about 3500 degrees F/ 1926 degrees C or higher, a strong investment mold is essential to withstand the heat and centrifugal force used in casting.
Wax removal – Burn Out
Steam de-waxing is not recommended when using the platinum investments.
The invested flasks are normally burned out in an oven. A 10 hour burn out cycle is usually used for phosphate bonded investments and a 5 to 6 hour burn out is used for acid bonded investments. The top end burn out temperature usually reaches 1600 degrees F / 871 degrees C. Be sure to follow your investment manufacturers instructions as to ramping and burn out procedures. The oven used to burn out flasks for platinum casting should have accurate temperature controls and a good air supply to allow complete combustion of wax residues. Most high production platinum casters use gas fired ovens.
Melting & Casting
Be sure to use a crucible made for platinum casting, graphite or carbon crucibles are not to be used for melting platinum. Check with your supply house for platinum melting crucibles. The life of the crucible will be limited due to the high temperatures used for melting. The induction powered casting machines use crucibles specially designed for that machine and are normally supplied by the machine’s manufacturer. For those using torch melting it is better to use a pre-alloyed platinum casting alloy as it is difficult to get a homogeneous mix when trying to make alloys in small melts with a torch. The pre-mixed platinum alloys come in shot, small squares or chopped rod shapes. Proper eye protection must be worn for melting platinum and a minimum # 10 welders goggles must be used, many prefer # 11 or #12 lenses for optimum protection. Permanent eye damage can result from inadequate eye protection due to the high temperatures used to melt platinum. Long sleeved heat resistant gloves and a leather apron will offer a measure of protection against the hot flasks, ovens and hot metal. For Torch melting the vertical centrifugal casting machines are preferred, the machine should be securely bolted to the floor. The preferred gas mix for melting platinum is Hydrogen and Oxygen that provides the hottest, cleanest flame. Propane and Oxygen or Natural Gas and Oxygen have also been used but melt times will be longer. Acetylene and Oxygen should not be used for melting platinum alloys due to the high carbon content in the acetylene. A screw on, multiport or rosebud torch tip should be used and the torch should have a built in flashback arrestor. A sharp, strong oxidizing flame should be used to melt the platinum, the flame should be concentrated on the metal not the crucible. The regulator settings for the hydrogen should be about 50 pounds and the oxygen 50 pounds. The regulator settings for propane should be about 5 pounds and the oxygen at 40 pounds. Keep in mind that a strong oxidizing (oxygen rich) flame must be used for melting platinum alloys, very much the opposite of melting gold or silver alloys. The molten platinum is normally cast at about 400 degrees F / 204 degrees C above the melting point of the platinum alloy, higher temperatures are used on light weight detailed castings. Platinum alloys will solidify quickly and an adequate amount of super heat is needed for casting. When torch melting, the casting temperature is usually determined by color and liquidity of the molten platinum alloy. In induction powered casting machines, optical pyrometers are often used or time at a predetermined power setting to determine the casting temperature. Some of the latest platinum casting machines have very sophisticated controls and programs to set pre determined casting temperatures.
should be adjusted to the size, weight and detail of the castings. A 1200 to 1300 degree F / 648 to 704 degree C flask temperature is used for heavy castings. A 1400 to 1500 degree F / 760 to 815 degree C flask temperature is used for medium weight castings. A 1600 degree F / 871 degree C or hotter flask is used on delicate light weight castings. The top flask temperature used for casting will be determined by the type of investment used, be sure to follow the instructions of the investment manufacturer.
Many casters will quench the flasks in water 10 to 20 minutes after casting. Great care should be used when quenching because the higher temperature flasks can generate steam and scalding hot water causing burns when put in water. Some casters prefer to wait until the flasks are a dull red color, hold them with tongs and use a hammer to knock the castings and investment out of the flasks by hitting the open ends of the invested flask, then quenching the investment covered castings in water. The platinum investment after burn out will resemble a fused concrete that is very hard and tenacious. It will take a lot of work to remove the majority of the investment from the castings by hammering and using a high pressure water gun or grit blasting.
The residual investment on the casting can be removed chemically by putting in a de-vesting solution consisting of 1 part Hydrofluoric acid to 3 parts water put in a covered, acid resistant plastic container. Be sure to read all the health and safety warnings before using Hydrofluoric acid as this is a very dangerous chemical. Proper eye protection and heavy acid resistant rubber gloves must be worn when using dangerous chemicals. Recently, some proprietary caustic alkaline de-vesting solutions have come on the market such as "J- Break" (Romanoff) that is put in a covered stainless steel pan and used hot. The hot caustic de-vesting solutions will remove the investment in 20 to 30 minutes. A homemade caustic de-vesting solution can be made using the following formulas;
Use Equal portions of the following liquid chemicals if available from a Chemical Supplier in liquid form.
Mix Equal Amounts of the Liquid Chemicals
- 50% Sodium Hydroxide Solution (Caustic Soda Solution)
- 50% Potassium Hydroxide Solution (Caustic Potash Solution)
- or -
Mix the Dry Chemicals and Water
- Sodium Hydroxide – (Caustic Soda) - Pels or Flake form - 3.15 pounds
- Potassium Hydroxide – (Caustic Potash) – Pels or Flake form - 3.15 pounds
- De-Ionized or Distilled Water - 1 gallon
Heavy chemical resistant rubber gloves and safety glasses must be worn when handling strong caustic chemicals, contact with the skin will cause severe burns. A large covered stainless steel pot is used to hold the caustic solution and a hot plate is needed to keep the solution hot ( 180 deg, F). A stainless steel mesh basket with a handle (French fry basket) can be used to hold the castings during de-vesting. When mixing the 50% Sodium & Potassium Hydroxide solutions, equal portions of each liquid chemical are put in the stainless steel pot and used hot. When mixing the dry Sodium and Potassium Hydroxide with water, slowly add the dry chemicals to the water in the stainless steel pot. When the dry chemicals are added to the water, a large amount of heat will be created, carefully stir the solution until mixed with a large stainless steel spoon. The heated caustic solution will take about 20 to 30 minutes to remove the investment. Do not use aluminum pots or utensils with caustic solutions. The castings should be well rinsed after de-vesting. When the solution slows down it should be replaced. To dispose of the caustic solution mix it with hydrochloric acid to adjust the pH to 7, filter the solution before disposal. The waste liquid will be sodium and potassium chlorides, salt water.
Investment Casting & Finishing Platinum Alloy Castings
Removal of Castings from Sprue Base
Castings should be removed from the sprue base carefully to avoid undercutting the casting or mechanical damage to the castings. It is best to leave a small amount of sprue on the casting to be removed by grinding or filing rather than risking damage to the casting.
Reuse of Casting Scrap
The sprue systems removed from platinum alloy castings can be reused in the next casts. Be sure all investment material is removed from the scrap before re-melting as silicon contamination can result from any attached investment residue. Keep the scrap platinum alloy in a separate labeled container to avoid mix-ups or contamination from other metals. Do not reuse platinum alloy scrap that has been soldered due to contamination from the other metals contained in the platinum solders.
Contamination of Platinum Alloys
Cracking in platinum alloys is usually due to contamination of the metal by other elements picked up during melting or finishing operations. Good housekeeping in areas used for melting, casting and finishing platinum alloys can not be overstated. Due to the high melting points of platinum alloys any tramp metal, silica, carbon or retained abrasives can be incorporated into the metal during the melting process. Small amounts of lead, tin, aluminum, arsenic, silicon, boron and magnesium can cause intergranular cracking. A reducing flame on torches used for melting or soldering can cause pick up of contaminants from refractory materials such as crucibles and support bricks. An oxidizing flame should always be used on platinum. Contaminated platinum alloys should be refined.
Repair of Minor Defects in Castings
Wire stock made of the same alloy as the casting can be fused into holes or minor defects on the surface of the casting with a torch, be sure to use an oxidizing flame and proper eye protection. A section of sprue can be fashioned into wire or strip and used to fill holes in the castings. Laser machines can also be used for repair work. The obvious defects in the castings should be repaired before finishing.
Platinum Finishing Area
Finishing work on platinum alloys should be done in a separate dedicated area. This will avoid contamination of platinum by other precious metals done in the same shop. It is wise to have a separate buffing machine and polishing wheels used exclusively for platinum finishing. This is also very helpful when scrap materials are recovered for refining as platinum bearing scrap material will be kept in one area of the shop.
Finishing Platinum Alloy Castings
Methods used for finishing platinum alloys require the use of progressively finer abrasives or compounds using a clean buff with fresh compound for each step. The usual sequence normally followed is to file edges and surfaces of the casting with # 5 or # 6 cut files. Avoid dragging the file on the return stroke. File marks and other surface imperfections are removed with silicon carbide or aluminum oxide abrasive papers starting with a 240 or 300 grit. Work sequentially through 400, 500 and 600 grit papers. Scotch stone and water can be used on hard to reach areas. The work piece should be thoroughly cleaned before burnishing with a polished tungsten carbide burnisher with a suitable oil or wetting agent on edges and surfaces. Buffing compounds used are bobbing compound with a course muslin buff and tripoli with a fine muslin buff. Bear-tex or a similar wheel can be used in place of bobbing and tripoli compounds for strong abrasion. For polishing, white rouge or Bendicks rouge with a soft muslin buff. Clean work piece after each compound. Keep buffs and wheels in separate marked containers. Check with your supplier about recently available Japanese compounds and polyvinyl acetate wheels said to give excellent results.
Casting Platinum Alloy Ingots for Sheet and Wire Fabrication
Casting Platinum & Platinum Alloy Ingots
Ingots may be static cast for plate, sheet and wire stock on a large or small scale depending on your needs. The platinum or platinum alloys can be melted by torch or in an induction furnace similar to methods used for investment casting and poured into suitable ingot mold. The small sized melts are torch melted and poured by hand. Large size melts are melted by induction and tilt poured. Proper crucibles for platinum are required and # 10 minimum welding goggles are needed for eye protection. The area used for melting and casting platinum ingots must be kept clean to prevent possible contamination of the platinum. The 10% Iridium / 90% Platinum alloy is frequently used for sheet and wire stock and the 5% Ruthenium / 95% Platinum alloy is often used for stamping ring blanks or other processes requiring machining.
Ingots cast in platinum or platinum alloys should be as thick as your rolling equipment can handle. Due to the rapid rate of solidification of platinum alloys, using thicker molds when pouring will help avoid cold shuts in the ingots caused by hitting the sides of the mold while pouring the metal.
Several materials are suitable for ingot molds for platinum, pure copper, 3% chromium copper or high purity graphite. The mold materials must be good conductors of heat, capable of pulling the heat out of the molten platinum. A preference for copper or 3% chromium copper has been noted as it avoids the possibility of carbon contamination from graphite. The molds will need to be custom made as none are available through supply houses.
A two piece L shaped mold with a base plate of the same material is used for casting ingots for plate and sheet stock. For wire and rod shapes a two piece rod shaped mold should be used. The mold must be 2 to 2 ½ times thicker than the ingot thickness to provide enough mass to act as a heat sink, pulling the heat out of the molten platinum alloy. If the molds are too thin, distortion, burning or melting of the mold can occur. Ingots of up to 100 troy ounces can be successfully cast in the solid copper, 3% chromium copper or graphite molds. Larger manufacturers use copper or copper alloy molds with water cooling jackets to dissipate the heat of the molten platinum alloys during the pour.
Casting the Ingots
The ingot mold should be pre-heated to about 250 degrees F/ 121 degrees C to drive off any moisture before using and placed on a sturdy metal table. No mold release agent should be used on the ingot mold for platinum alloys. The mold should be securely clamped with a C clamp. A high intensity spotlight should be directed at the top of the ingot mold to make it more visible when wearing dark # 10 welders goggles. Some workers will put a little talc or chalk on the top of the mold to make it more visible when pouring the molten platinum alloy. For small ingots a Hydrogen / Oxygen torch with a strong oxidizing flame should be used with a suitable crucible to melt the platinum alloy keeping the flame directed at the metal. When the molten platinum alloy has reached an adequate amount of super heat (400 degrees F / 204 degrees C) above melting point, it is poured into the mold with a quick steady pouring motion. It is important to try to avoid hitting the sides of the mold during the pour and slow down at the end of the pour to avoid deep shrinks in the top of the ingot. Some smaller manufacturers build small devices to hold the crucibles with a hinged tilting device directed into the ingot mold to facilitate pouring the molten platinum alloy. Larger manufacturers use high frequency induction furnaces with zircon crucibles packed in Insul-oxide sand placed in a silica based liner. Tilt pouring is usually done with the large high frequency furnaces. Platinum alloy ingots should be quenched in water quickly after casting. All areas used for casting platinum alloys should be kept clean to avoid contamination from other metals.
Fabrication of Platinum Alloy Ingots
Platinum alloys are normally cold rolled to make flat stock and swaged, rolled or drawn to make wire stock. 50% to 70% reductions in size are taken before annealing. Reductions of less than 30% between anneals should be avoided as light cold work and frequent anneals can cause grain growth resulting in an orange peel surface effect. Most platinum alloys will have cold working characteristics similar to 18 karat yellow gold alloys.
Platinum alloys can be hot rolled, forged or hammered. Most of the hot rolling is done in large manufacturing operations working with large ingot sizes. The platinum alloy ingots are heated above the annealing temperature (usually 1100 degrees C / 2012 degrees F to 1200 degrees C / 2192 degrees F) and rolled to 70% reductions before re-heating the ingot. Hot rolling allows rapid reduction of thick ingots.
Annealing Platinum Alloys
Most of the platinum alloys will be fully annealed at 1000 degrees C/ 1832 degrees F. The usual oven anneal time will depend on thickness and is usually 15 to 20 minutes. Most platinum alloys do not oxidize and ovens with reducing atmospheres should not be used on any platinum alloy. For torch annealing, the platinum alloy should be evenly heated to a bright orange with an oxidizing flame. Most platinum alloys can be air cooled or quenched in water, the exceptions would be Platinum / Ruthenium and the heat treatable platinum alloys that need an immediate quench in water for optimum softness. Avoid frequent or long anneal times on platinum alloys as it can cause excessive grain growth that will cause a rough, orange peel surface.
Rolling Mills used for Platinum Alloys
All rolling mills used for platinum should be cleaned before the platinum alloys are rolled. It is very helpful to vacuum and wipe down the machine to pick up any chips or small pieces of other metals on the rolling equipment. Any small chips of gold alloys imbedded in the platinum alloys during the rolling process will be melted into the platinum during the annealing which is above the melting point of most gold alloys. Platinum alloys have a tendency to smear or build up on the rolls in rolling mills. The rolls should be cleaned before and after rolling platinum alloys. A helpful device to clean the rolls is made using a large wooden dowel about 1 ½ inches in diameter by 2 inches long, a heavy leather strap 2 inches wide by 16 to 18 inches long and a strip of emery paper of the same size as the leather strap. The rolls are opened wide and the leather strap is placed around the wooden dowel with the emery paper put over the leather strap. A light oil is put on the rolls and the leather strap with the emery paper is inserted between the rolls tail first. The rolls are closed until barely touching the emery paper covered strap and the rolling mill turned on. The wooden dowel can be held to move the strap back and forth over the roll surface to remove the build up on the rolls. The rolls should be wiped clean after the build up is removed.
Wire Rolls and Dies used for Platinum Alloys
All equipment should be cleaned before running platinum alloys to remove any chips or particles of other metals. Wire rolls can be cleaned to remove any build up from platinum alloys using a pointed wooden stick to hold emery paper against the lightly oiled grooves on the reverse side of the machine. Carboloy wire dies can be cleaned using a waxed or oiled string dipped in emery powder using a back and forth motion until build up is removed. The rolls and dies should be wiped clean with a solvent after removing the build up from platinum alloys.
Soldering Platinum Alloys
Soldering Platinum Alloys
Techniques for soldering platinum alloys are very different than those used for soldering karat gold alloys. Due to the poor conductivity of platinum, a hot flame is used directly on the joint and solder rather than heating the whole piece. #6 to #10 protective welders glasses or goggles must be worn due to the higher temperatures used for joining platinum alloys. An oxidizing torch flame is used on platinum alloys rather than the reducing flame used for karat gold alloys. Alumina or Zircona brazing pads should be used instead of the charcoal blocks used for gold alloys. A tungsten pick and tungsten tipped tweezers should be used for platinum alloys due to the higher temperatures used in joining the metal. The work area used for platinum joining should be kept clean as the soldering temperatures used for platinum are above the melting point of gold alloys and any bits of gold alloy will melt into the platinum alloy. Make sure platinum alloy pieces are fitted properly before soldering as platinum solders do not fill gaps. Use a hot flame directly on the joint and solder, heat the joint quickly, if the platinum is not hot enough to cause fusion the joint will break on hammering.
In the jewelry industry the term solder is used but in reality they are brazing alloys. The platinum solders are formulated to melting points and are listed according to their melting point in degrees C. The standard platinum solders come in 1000, 1100, 1200, 1300, 1400, 1500, 1600 and 1700 degrees C. The best color match is obtained with the 1700 making it the best choice for sizing. Flux may be needed on the 1000 to 1500 solders to protect the solder from oxidation. No flux should be used on the 1600 and 1700 solders. Pure platinum is sometimes used to weld 10% iridium / 90% platinum alloy.
Sources of Further Information on Platinum
Booklets Available: Two excellent booklets entitled "An Introduction to Platinum" and " Platinum Tech Tips " are available from;
608 5Th Avenue
New York, N.Y. 10020
Phone (212) 245 6790 Fax (212) 541 5633
Platinum Guild International U S A
620 Newport Center Drive, Suite 800
Newport Beach CA 92660
Phone (949) 760 8279
Fax (949) 760 8780
Technical Hotline (949) 760 8882
Trade Website www.pgi.platinum.tech.com
The Orchid Website
|Platinum Alloys Used for Jewelry|
|95Pt – 5Cu||950||20.0||1725° C||Gen. Purpose & Casting – Ger.|
|95Pt – 5Co||950||20.8||1750° C||Fluid for Hard Castings -U.S. Eur.|
|90 Pt/3 Co/7Pd||900||20.4||1730° C||Hard Castings - Japan|
|90 Pt/5Co/10Pd||850||19.9||1710° C||Harder Castings - Japan|
|95.5 Pt/1.5In/3Ga||950||19.3||1650° C||Hard, Springy can be Cast|
|95 Pt – 5 Ir||950||21.4||1780° C||Gen. Purpose & Casting|
|90 Pt – 10 Ir||900||21.5||1790° C||Gen. Purpose & Casting - U.S.|
|85 Pt – 15 Ir||850||21.5||1800° C||Gen. Purpose, Hard|
|80 Pt – 20 Ir||800||21.6||1815° C||Gen. Purpose, Harder|
|95 Pt – 5 Pd||950||20.8||1755° C||Castings – Very Soft|
|95 Pt - 5 Ru||950||20.7||1780° C||Gen. Purpose, Good Machining|
|95 Pt – 5 W||950||21.3||1830° C||Hardenable for Springiness|
|90 Pt – 10 Pd||900||19.8||1740° C||Gen. Purpose, Soft - Japan|
|85 Pt – 15 Pd||850||19.1||1730° C||Chain Making – Japan|
|58.5 Pt - 36.5 Pd - 5 CuPt||585||15.4||1580° C||14 kt Platinum – U.S.|
|99.9 Pt||1000||21.4||1773° C||Stamped Pt 1000 – Japan|
|99.0 Pt||990||21.4||1773° C||990 Fine, Chuk Pak Gam – H.K.|
Co – Cobalt Cu – Copper Ga – Gallium In – Indium Ir – Iridium Pd - Palladium Pt – Platinum Ru - Ruthenium W - Tungsten
Note: – Check Platinum Fineness regulations in the Country where jewelry is being sold.
Precious Metal Spot Prices
|Gold||2020-01-23 8:39 AM|
|Silver||2020-01-23 8:39 AM|
|Platinum||2020-01-23 8:39 AM|
|Palladium||2020-01-23 8:39 AM|
Prices shown are for reference only. Please contact our trading desk for accurate, up-to-the-minute pricing.