Article on platinum alloys

[Matata]

For those of us who love the white metal

 

[SeaOats]

Cool article! We always have questions here on PS about platinum alloys. Now there''s another article to send them to!

 

[Garry H (Cut Nut)]

Hmmm.
We have been looking into Rhutidium paltinum 950 adn we are getting mixed messages.

We would like to know of any other info more specific to hand working if anyone can help please. But first let me share:

One of my team of 6 hand fabricating jewellers who occasionally also use cast components had worked with Ru Plat in South Africa and was not happy with it.

Here is his rather long discussion:

Hiya Stella

I had a look at the platinum you sent over yesterday and im afraid to say it looks pretty much exactly the same as what ive worked with before, I examined the ring you sent over and it didn’t take long to find the telltale porous sweat join, this metal does not like to sweated or fused by conventional X or V fusing but rather by a much shallower fuse at a lower temperature. I melted a little ball which settled into a crystalline formation as per the Ruthenium platinum I have worked with before as well. Unfortunately I have to say that I cant see any improvement over this alloy from the Metal Concentrators or the CPM one.

In my chat with the metallurgist from Johnson Matthey he was rather adamant that the alloy shows no age hardening or metal memory characteristics which could result in shanks or settings warping over a period of time. However. Please find attached data sheets from Metal Concentrators which show as follows.

PlatRu Standard Annealled hardness 135 HV and Aged Hardness 170 HV

PlatRu Advanced (sic bwaaaahahahahahahaha) Annealed 150 HV and aged 190HV

PlatCu shows 0 age hardening

This shows an average age hardening of about 26 percent from its annealed state, and herein lies the problem, if you roll a shank down considerably the metal definitely develops a linear grain, which in itself isn’t a problem, but when you solder or fuse it together the relevant joining area is annealed and will age harden and show movement in the direction of the rolled grain over a period of time.. IE shanks will tend to try straighten themselves out, tubes will tend to lift over set areas resulting in stones somehow magically becoming loose after being well set. As I am not a metallurgist I cannot say that the local PlatRu will show the same characteristics and there is some degree of supplier error or production error to factor into that.

I have no way of proving metal memory in this alloy other than a few years of experience struggling with the metal. I never had these problems with the Copper or Iridium based platinums.

The resolution to this problem would seem simple, solder the joins with low heat solders to reduce annealing the finished workpiece, ummmmm next problem… most the softer solders tend to be very grey in comparison to the alloy the join is always very visible in terms of color and definitely poses a polishing problem.. The alloy does polish beautifully and is definitely a better finish than the other PT alloys, but to get that good finish requires more buffing which in turn means you put pressure on the solder creating a visible dip at the solder line. This problem is easily overcome by finishing the piece by use of 3M platinum grade polishing cloths ranging from 2000 grit through 8000 grit before buffing and applying a final finish with Blue Magic polishing paste on a soft mop. ( so add about an hour of polishing time to labour quoted on PlatRu alloys), or alternately put your joins in places where they aren’t visible or wont require hard polishing, and or Rhodium plate the job. This last option negates the point of working in a whiter platinum alloy. And assuming all goes well, what do you do when the job comes back for sizing? Solder with soft solder and leave a definite join? Or risk surface burning the stones to get the join clean.

This problem was finally addressed by the alloying company and they released a set of special solders for Ru alloys which you will also find on the attached data sheet, and, well, its also a mixed success, the solders definitely work better and tend not to leave visible joins but are “sweat” solders and tend not to run very well. The lower temperature solders showed a tendency pit your join on thinner objects like wire (sort of flowing some of the metal along with the solder into the join leaving a hollow depression next to the join). This is a problem in clusters and fine wire or bridging work. The best solder is the platinum nominal 1700 solder which I used with great success. The down side to this solder however is increased work time due to its high melting point. No flux or binding agents can be used because at 1700 c they cause a matt finish on the soldered surface so to hold your solder in place when you use a very high pressure flame to achieve a 1700 c solder is rather tricky and frustrating, mostly you tend to “blow” the solder off the join before it can bond. Thinly filed titanium tweezers are very usefull here unless you are doing fine wire work where you cant get a tweezer into the join to hold the solder in place. A low tech tip I was given was to use spittle on the join…. ( never tried it, and please I don’t want to go down in the same books as the other guy who worked here and recommended earwax for burr lubrication.)

(PS. Using lanolin oil instead of bee wax tended to work better for burring and drilling platinum)

On the plus side the alloy is fantastic for doing wire work and other fine stuff where the softer platinum alloys will tend to bend or create corrugation on bent surfaces this platinum in its hard state can be bent acutely without loosing its polished state or creating the corrugation problem. In the my last workshop we used a lot lot less platinum per job due to cost constraints so this platinum was ideal in terms of being able to make thinner shanks which weighed less without risking the structural strength of the ring. Its polish is fantastic and it keeps its polish a lot longer than the CU alloys. If you are a bit careful about planning your job and getting all your joins into places where they wont be visible this is definitely a superior metal. Some of my friends have worked around the problems of this alloy by making all the components separately and attaching them by using normal 16%PD white gold solders at low temperatures.

I don’t know what to recommend to you as regards this alloy, I have have mixed results ranging from fantastic to utterly disastrous. I have had report of at least 4 pieces having returned to my last workshop in some state of breakage. Once again I cant say for sure that it isn’t due to to fabrication error on my behalf, but I can say that not a single PlatCu piece has ever been returned.

Have a good day

Cheers Chris

 

[Bluehammer]

Does anyone have some comparision pictures of these metals? I am just curious.