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Technical Questions and Answers

Welcome to PGI's Technical Questions and Answers forum. Here you will be able to see many of the most common questions regarding platinum casting, sizing, stamping, and how to solve technical issues that are giving you problems.

Please see the current topics below.  If you would like to add a topic for discussion, please email us at platinumconcierge@pgiglobal.com.

I accidentally melted some gold into my platinum, what do I do?

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.

I am in the process of making two platinum wedding rings and am at the stage of annealling the metal. I currently use a micro-torch which heats up to a maximum temperature of 1300 degrees C, but am struggling to get the platinum hot enough (the metal is not changing color at all). Could you tell me if the torch I am using is hot enough to get the platinum to the correct annealling temperature?

Are you using oxy/propane with your torch? The metal should be bright orange in no time. I think you may have to use a different torch if this one is not getting hot enough. You will need one anyway to weld the bands do you not? Another option would be to set a kiln at 1000c and place the bands inside for annealing.

What casting machine do you believe is best for a company casting 3-4 flasks twice a week?

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.

I have a consumer who wears a white gold diamond band next to her platinum engagement ring. The diamonds from the band are rubbing against the prongs in the engagement ring and are damaging them. Why is this happening and how do I fix it?

A diamond, the hardest substance on earth, will cut through anything when given the opportunity. Platinum jewelry, as with any fine jewelry 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.

What do the terms ductility and malleability mean?

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.

Why does some platinum jewelry appear to be magnetic?

Jewelry made from platinum 950/cobalt alloy is slightly ferro-magnetic, but is acceptable to use for jewelry production. This alloy is commonly used when a fine, detailed casting is desired.

What is the melting temperature of platinum and other popular alloys?

  • Pure Platinum: 3224F or 1773C
  • Pt950/Ruthenium: 3250F or 1788C
  • Pt950/Iridium: 3236F or 1780C
  • Pt900/Iridium: 3236F or 1780C

Why is platinum made with different alloys like iridium or ruthenium? Is there a desired combination of alloys for fine jewelry?

Platinum in its pure state is very soft and cannot be used for jewelry. 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 jewelry will scratch, bend and dent easily.

Recently I experienced some problems soldering a Platinum/Cobalt engagement ring to a Platinum/Iridium anniversary band. I used 1300 platinum solder to join the rings, everything seemed fine, they looked great. Two months later they have completely separated. I have never had two rings come apart so I'm wondering if I should have used something different to solder these two alloys together. If you have any suggestions please let me know.

One of the issues here is the fact that Pt/Co oxidizes. Most likely, when you soldered the two rings together, it took a little too long and the solder melted and attached to the oxide instead of the platinum. Then, after a little wear, it simply broke off.

As you know, 1300 Pt solder contains no Pt at all, but is a mixture of silver and palladium and copper. The cobalt will begin to oxidize at about 1000 C., so the 1330 C solder will be inside the oxidation range. For this reason, I recommend you use a hard WG solder, which melts below 900C and thus is outside the oxidation range of cobalt. Also, in that case you would need flux (which you would NEVER use over 1000 C.

A consumer is complaining about a platinum ring deforming and scratching. Why is this happening?

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.

Where is platinum mined?

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.

What does the stamp: IRIDPLAT signify?

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.

What is the best way to polish platinum?

  • 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.

Why is the porosity when casting much more apparent in platinum compared to 18kt gold?

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.

What is the difference between PT950 and PT1000 rings?

PT950 means that there are 950 parts of platinum in a 1000 mix ( 50 being an alloy to make the metal harder or more durable.) Pt 1000 means that there are almost 1000 parts of Platinum in a 1000 mix. It is actually 999.2 or so, with the very small difference being micro alloy for hardness.

Whats's the difference in terms of vickers hardness for both types of rings (PT1000 vs PT950)? I'm interested in A PT1000 wedding band but worry it may not be able to withstand the hard knocks as I work in A factory.

The hardness of Micro alloyed Pt 1000 alloys is actually more than standard alloys. As long as it is not heated past annealing state. I would ask the merchant for the hardness I think it is around 160HV for the 1000 and 110 to 135 HV for the 950 depending on the alloy.

How do I size a platinum ring one size smaller?

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.

Tips on what not to do:

  • 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

How do I size a platinum ring up?

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.

THINGS TO CONSIDER:

  • 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).

When should I solder, and when should I weld platinum?

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.
Note on sizing:
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.

Can welding or soldering a platinum ring be done near stones?

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.

Which platinum alloy can be used universally?

Platinum alloyed with 5% Ruthenium is the universal alloy of choice. Pt950/Ru is 130 HV hard, has excellent color 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 luster.

What are PGM's?

PGM is the acronym for Platinum Group Metals refers to the group of metals commonly found along side of platinum. There are a total of 5, which are: palladium, osmium, rhodium, ruthenium and iridium.

When was platinum declared a strategic metal?

During the second World War in 1939 Europe declared platinum a strategic metal. The UK made this declaration as well during the same year.