Ruthenium or Cobalt

[my secret]

Ruthenium or Cobalt Platinum 950

I am interested in a comparison of the two, benefits, weaknesses, colr, etc.

 

[stone-cold11]

John wrote this article.

http://journal.pricescope.com/Articles/47/1/An-Overview-Of-Common-Alloys-Used-In-Jewelry.aspx

Pt950/Ru (950 parts platinum, 50 parts Ruthenium) is very hard. It has the highest melting temperature of all platinum alloys and is difficult to cast. Darker gray in color than platinum-iridium, it is less malleable, hard to solder and weld and hard to burnish. Bench workers find it tough on burs, files and drills. Some setters recommend it for diamonds only, since more pressure must be imposed on gemstones during the setting process. It is extremely scratch & bend-resistant and extremely resistant to signs of wear over time.

Pt950/Co (950 parts platinum, 50 parts Cobalt) is moderately hard. With the lowest flow point of these alloys it is good for even, dense castings of finely detailed pieces or filigree but not for work by hand. This alloy tarnishes when heated so it needs flux and pickling after soldering just like gold, unlike other platinum alloys. Since Cobalt is a ferrous metal, not from the platinum group, its scraps must be kept separate from other platinum scraps. It takes a fast polish but finishes darker gray than iridium. It requires moderate pressure on gemstones during the setting process. Bench workers find it more "gold-like" and easy on the tools. It wears quite well over time.

Hardness = HV

Often referred to as "scratch resistance," hardness is measured using the Vickers Hardness scale. This tests the hardness of a metal by pushing a pointed object into the surface with a specified load and gauging penetration.

Durability = PSI

Tensile strength, or durability is measured in pounds per square inch.

Comparisons

* 18K Gold = 125 HV…29,000 PSI
* Pt900/Ir = 110HV…55,000 PSI
* Pt950/Ir = 80HV…40,000 PSI
* Pt950/Ru = 130HV…66,000 PSI
* Pt950/Co = 135HV…64,000 PSI

Gold is harder than some platinum alloys and will resist scratches better. Platinum is almost twice as durable as gold, is more ductile has much greater longevity. For the body of the piece the differences are not critical. For the prongs they have implications: For instance, white gold prongs will break. Yellow gold prongs will bend more, as will platinum, but platinum prongs are more durable over time.

All from the above link.

 

[diamondseeker2006]

I believe Tiffany and Leon Mege use Platinum/ruthenium. My platinum/ruthenium rings are extremely white and resist scratches wonderfully!

 

[John P]

Date: 9/19/2008 5:16:07 PM
Author:my secret

Ruthenium or Cobalt Platinum 950

I am interested in a comparison of the two, benefits, weaknesses, colr, etc.

It all depends... For what kind of piece? Hand-worked or cast? Delicate or heavy? Complex or simple?

Platinum is alloyed with other metals for two reasons:1, to bring down its melting point and 2, because in its pure form it’s too soft.There are infinite variations beyond the several I mentioned in the article (thanks for the link Stone-Cold). The choice depends on preferences and what effects the metalsmith is trying to achieve. Platinum-ruthenium has the highest melting point of the alloys I mentioned but it’s more millable, so it can be machined and grinded better.Many milled products are plat-ruth because it is harder and crisper at the bench.Platinum-iridium has a lower flow point and is fabulous for casting, but is more difficult to hand-tool and wears softer. Platinum-cobalt is great for mass-production but cobalt is a ferrous metal, not from the platinum group (its scraps must be kept separate from other platinum scraps) so it is not in the "noble" family of platinum alloys.

My ring is Plat-Ruthenium. It wears as DiamondSeeker reported (and I am a typical guy). My wife's ring is Plat-Iridium and she would say the same about hers even though it's a bit softer. Of course that lady is graceful in everything she does whereas I tend to clunk about.

 

[elle_chris]

My wedding band is 950Pt/Tungsten. I noticed this mix is never mentioned, any reason why?

 

[John P]

Pt-Tungsten is one of a number of specialty alloys that goes through a further process of heat treating/aging to change its hardness. Some harden all the way to HV200+ (the same range as stainless steel and titanium jewelry). Nothing wrong with that, but since they behave more like tool steel than precious metals you don't find them categorized with the common platinum jewelry alloys.

 

[my secret]

Most of the information I can find, like what has been mentioned here, is directed toward how it is to work with the different alloys.

What I would like to know is if you have two rings identical in all ways except the alloy, what differences you would see between the two as far as durability, finish/polish, and color. From what I have read they almost sound the same with the exception of being ferrous.

Thanks.

 

[my secret]

I need to make a choice on this ASAP. Can anyone tell me what the differences between these two alloys would be?

 

[my secret]

I was able to find my own answer on Mark Morrell''s website. I thought I would post it in case anyone else is interested. Here is an excerpt from Mark''s website:

http://www.mwmjewelry.com/platinum_purity.htm

"2) 95% platinum (950) - alloyed with 5% ruthenium - Vickers hardness = 135

Ruthenium has an atomic weight of 101.07 - a bit over HALF the weight of iridium

By VOLUME, we''ll need almost twice as much ruthenium to equal the weight of the iridium in the above "950" iridium example.

This alloy is fairly hard - resists dents and dings well - is less malleable - is resistant to wear and abrasion but prone to cracking and requires more pressure to be imposed on a stone during the setting process than the softer alloys. When it doesn''t crack, it features all of the longevity that platinum is renowned for. This alloy works reasonably well for both casting and hand fabrication - when it doesn''t crack. This is a very good alloy for machine cut parts.

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3) 95% platinum (950) - alloyed with 5% cobalt - Vickers hardness = 135

Cobalt has an atomic weight of 58.933200 = roughly only 30% of the atomic weight of platinum and iridium.

When we consider the VOLUME of this element required to equal 5% of the weight of our platinum, we need almost 3 1/3 times the volume of our iridium to generate 5% of our platinum by WEIGHT.

This alloy is fairly hard - resists dents and dings well - is not reasonably malleable or workable at the bench - is much less resistant to wear and abrasion than the iridium and ruthenium alloys - lacks longevity because of it''s LACK of resistance to wear and abrasion and will require that more pressure be imposed on a stone during the setting process. This alloy works extremely well for casting. This metal polishes quickly because polishing is "abrasion" and the alloy doesn''t resist abrasion as we''d otherwise expect platinum to do. This alloy features a natural "bluish" color cast due to the high volume of cobalt. Rhodium plating is often employed to hide it''s native color. This metal it is magnetic. You can actually pick up a piece made of this metal with a strong magnet. Welding and hand fabrication have proven to be problematic for bench jewelers / repair technicians."

This was actually one of the best resources I could find related to this in fact, I may have changed my mind on a setting.

Thanks.