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For technical assistance, scroll through the list below of common technical questions and answers. If you have a technical question that is not listed, please contact ukinfo@pgiglobal.com.
It is difficult to predict the reaction of platinum in a mold at high temperatures when casting. However, with simple fine-tuning, the process can be perfected.
Many production casters believe it is easier to deal with porosity after casting by using lasers. If you use one alloy and set your quality standards high, casters should be able to get the parameters right and give you a good product. While it is not possible to cast without some porosity, a good
caster has ways to reduce it to an absolute minimum by controlling the casting parameters.
 Pure Platinum: 3224F or 1773C
Pt950/Ruthenium: 3250F or 1788C
Pt950/Irididium: 3236F or 1780C
Pt900/Iridium: 3236F or 1780C
This is an older stamp that refers to 900 platinum/100 iridium alloy that was used until the mid 70s. Today, the same alloy is stamped Pt900, 900 Pt or 900 PLAT, as established by the Federal Trade Commission.
It is not possible to weld near stones using a torch. Even the lowest temperature platinum solder will burn the stones. However, it is possible to weld using a laser next to stones. At times, soldering can be done with a gold solder when replacing a head on a semi-mount.
Jewellery made from platinum 950/cobalt alloy is slightly ferro-magnetic, but is acceptable to use for jewellery production. This alloy is commonly used when a fine, detailed casting is desired.
Platinum is found mostly in South Africa and Russia. There are also smaller mining operations in the U.S. and Canada. Alluvial platinum (platinum found above ground) is found in the rivers of Columbia as well.
PGM is the acronym for Platinum Group Metals, which refers to the group of metals commonly found along side of platinum. There are a total of five, which are: palladium, osmium, rhodium, ruthenium and iridium.
Ductility is the ability of a metal to be elongated, as in making wire and drawing.
Malleability is the ability of a metal to be forged, bent, formed, and thinned by rolling. Platinum is a very ductile and malleable metal.
A diamond, the hardest substance on earth, will cut through anything when given the opportunity. Platinum jewellery, as with any fine jewellery is not immune to this. Since a band and engagement ring are constantly rubbing together when the wearer moves their fingers, the diamonds can scratch and damage the surface of the engagement ring. Damaged prongs may have to be replaced. But if the rings are soldered together, the damage can be minimized.
Platinum in its pure state is very soft and cannot be used for jewellery. In order to give it hardness, platinum is alloyed. To determine which alloy to use, first look at the manufacturing method.
The best choice for universal needs, such as casting, fabricating, die striking, etc. is Pt950/Ruthenium. This hard, malleable and ductile alloy is the alloy of choice for many high end manufacturers.
For hand fabrication, Pt950/Iridium is a good choice, as the metal is work-hardened by hammering and rolling it.
For casting, Pt900/Iridium is a good choice, as Pt950/Iridium may be too soft and the piece of jewellery will scratch, bend and dent easily.
1. Using a side cutter, cut the shank from the right and then the left. This will create two opposing pointed ends. Spread the shank open to the desired size using a mandrel.
2. Cut a piece of sizing stock to the required length for the desired size. Using a saw, cut a V-shape on either side of a piece of sizing stock. File it to fit on the shank ends. Check for fit.
3. Insert the piece of sizing stock into the ring. Be sure it fits snug.
4. Using hard 950 platinum solder, solder the piece of sizing stock to the shank. Be sure solder flows all around.
5. After filing the inside, round the ring on the mandrel. This will also work-harden the shank for easier finish.
6. File, sand, and polish the ring after the dove tail sizing.
Pick sizing stock of the same alloy as the ring to assure color match.
Pick sizing stock of the approximate dimension of the actual ring. This will reduce filing and waste.
Be aware of stones in the ring. You may need to protect or remove them before sizing.
Make the ring about 1/4-1/2 sizes small and hammer the shank to the proper size. This will harden the shank and finishing will be easier.
Remove all scratches with fine abrasive paper before polishing.
Be sure and replace the quality mark (Pt950).
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When polishing platinum, it is important to remove all scratches before the polishing process.
When filing, file gently with a diagonal movement. Then repeat with a diagonal movement perpendicular to the first one.
Remove file marks with abrasive paper such as 400, 600, and finer paper.
Be sure to use the files and abrasive paper only on platinum to avoid contamination.
Reduce the surface to at least a 600 grid finish on the bench.
Burnish the ring with a polished tungsten burnisher.
Use platinum polishing compound only for luster.
Use 2000, 4000, and 8000 grid polishing compounds.
When polishing platinum that is joined to gold, be sure the platinum is polished completely before polishing the gold.
Check with tool suppliers for brand recommendations.
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The essential features of a quality sizing are: a proper fit, invisible seam, and an even shank thickness. The following procedure will leave no seam and is totally invisible.
1. Cut the ring and remove 2.54 mm of shank. Bend the ring together until the ends meet.
2. Using a three square file, file a chamfer (v-groove) along the seam. This ensures a complete fill of the seam during welding.
3. Roll the piece just cut out from the ring through the rolling mill making it approximately .5 mm thick. Cut a small piece from this and wedge it into the gap with
the chamfer groove. It should stick out approximately 1 mm, evenly around the cross section of the shank.
4. Wearing #5 welding goggles, use an oxidizing flame of a propane/oxygen, hydrogen/oxygen or natural gas/oxygen mix and melt the over hanging metal all around the seam, filling the gap as it melts.
5. Quench or let cool, gently file away excess metal, and round the ring.
6. Clean and polish. Be sure there are no scratches, pits, or marks. Check size and make adjustments if necessary. Because the metal used to fill the gap was from the host ring, there will be no seam, therefore sizing is invisible.
Don't use Acetylene Gas. Only Natural Gas, Hydrogen or Propane will work for Platinum
Don't weld without eye protection. UV radiation WILL damage your eyes
Don't weld when stones are nearby. The welding process will damage most stones
Don't use your soldering pick or steel tweezers near the flame, as they may contaminate the platinum
Don't weld on a charcoal block. Platinum and carbon do not get along
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We do not recommend machines by brand names. However, a small operation machine using a vertical centrifuge would be able to do cast 3-4 flasks twice a week. You may want to try hydrogen/oxygen or propane /oxygen fuel with a multi-port torch. For eye protection, use at least #10 welding goggles.
Soldering is usually required when you are working on a multi-metal piece, such as an 18K and platinum combination. The metal with the lowest melting point dictates the method used. Soldering is also preferred when attaching minor components to platinum, such as findings.
Sizing a platinum ring is normally done by welding, as long as there are no stones nearby and the ring is made entirely of platinum. When you need to use solder to size a ring, use a 1700 seamless solder or a high purity "plumb" solder. Lower temperature solders tend to show a seam.
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When annealing platinum, it is easy to contaminate the metal by melting in stray filings, solder chips, or any other metal on the bench. If this happens, use a ball burr and grind the contamination away, similar to the way a dentist cleans a cavity. Then take a small piece of the same platinum alloy the object is made of and weld it to fill the hole. Filing the excess metal away, you create an invisible repair. To prevent this contamination from happening, be sure to steam or sonic clean your platinum before welding or soldering, and clean the bench prior to heating the piece.
Platinum alloyed with 5% Ruthenium is the universal alloy of choice. Pt950/Ru is 130 HV hard, has excellent colour and is 100% precious metal. It is used for casting, fabricating, machining and die striking. Most of the machined wedding bands sold in the U.S. are made from this alloy, and because of the hardness it will take on a very high lustre.
Platinum must be alloyed with another metal to provide the best high purity alloy. Depending on what type of manufacturing method will be used, some alloys are more favorable than others.
For example, an alloy that is very soft may need to be work-hardened or heat treated to become harder. These alloys are ideal for die striking or hand fabrication, where additional work is being done resulting in a harder piece. However, casting usually requires little work and produced pieces may just need to be cleaned and polished. For this method of manufacturing, these soft alloys are less suitable.
Depending on which alloy was used and which manufacturing, a ring such as the above in question may have been cast from Pt950/Iridium or Pt950/Palladium, which have a hardness of only 80 and 65 Vickers respectively. |
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