Soldering, (as opposed to welding) is using a low temperature material to bond or fill materials in an item.
WHAT DOES "PLUMB" MEAN IN SOLDERS?
When the precious metals content in the solder matches or is superior to the jewelry, we call it plumb. Otherwise we call it "repair" grade solder. Different makers of solder use somewhat different terminology for low karat solders, but plumb always means at least matching the precious metal content between the solder and the jewelry.
As we know, platinum jewelry normally runs from 90% to 95.2% Pt. To understand plumb" platinum solder, I must also talk about gold solders a bit for comparison. When we consider gold jewelry in the United States, we see gold content run from 41.66% (10K) to 75% (18K) with some exceptions. You can see that in nearly all instances, we have a lot of alloy to work with in creating solders for gold compared to platinum. For decades now we have been accustomed to gold solders that run in gold content from 25% to 80% gold. For 14K, or even 18K, we have a lot of alloy we can use to get the color, strength and low characteristics we desire. What we call "repair" solders in gold and platinum, the precious metal content is adjusted solely for either melt and color, or at the wholesale level price.
In what should be called "platinum repair" solders, a necessary lack of Platinum causes the addition of substitute metals intended to pull down he flow temp while providing color and strength. All of us in the platinum solder trade use substitute metals for flow and or color. Lets examine the metals we commonly substitute for platinum in solder.
1.Nickel-Remember all the trouble cause by Nickel in white gold? We usually work to keep nickel out of jewelry where it is practical to do so. Europe prefers no nickel at all.
2.Silver-This is hardly a metal commonly associated with platinum jewelry, but it provides important properties to conventional platinum solders.
3.Palladium-Too high a melt temperature to help much at all, but it is the very common element found in higher temperature solders. In recent months cost has become a big factor with this important element.
4.Gold-Wrong color and too high a temperature to solve the flow.
These metals do have shortcomings. Poor color, porosity and some very visible seams just to name a few. This is often fixed with rhodium plating, but that is another unneeded expense, and rhodium will wear off with time, which can disappoint the buying public. Due to the unique nature of platinum, we always had to compromise the platinum content of the solders. Sometimes in the higher temps we find some Platinum but only rarely below 1500C. In these solders we do not find platinum content even closely approaching the content in the jewelry. At 1500°C there is typically from 10% to as little as 0% platinum content.
Platinum solder rarely really deserves the title platinum. Platinum, as we well know from bench work and casting is a very different animal than gold. Astronomic temperatures cause all kinds of difficulties.
In late 1998 rumor had it that the new "Heat treatable" S+Ô platinum developed by Steven Kretchmer melts below 1700°C. perhaps close to 1600°C. –This was the first commercial casting grain with the lower flow temperature. Once the fact that this could be done at all was commonly known, many possibilities emerged and will continue to do so. The possibility of using that metal as a solder came straight to mind, but a solder that is too hard creates problems for finishing, and 1600 is not a very low temp for a good Pt solder. But the seed was planted.
I suggested that if we applied 30 years of solder making knowledge to the principles found in S+ and published JM alloys, we could develop "plumb" platinum solders. After taking a look at our own solder formulas ideas took real shape.
My feeling was that for a viable line of products we needed "easy" "medium" and "hard" grades of solders. That means three distinct flow temperatures, all as low as possible. Keith was able to invent one kind of viable alloy that did what we needed. The obvious thing to do was vary the Pt% for flow temp purposes. There were many things to evaluate. We discussed a few formulas. When creating a new product your best people are critical. Robert Lumabao brings 10 years of shop experience to the task. Keith Weinstein gave the initial test formulas to Robert, who began with the 95% Pt solder.
As Robert worked his way through some predictable properties emerged. The higher Pt content material is easier to roll out than the lower. This is consistent with solder manufacturing in gold. The metals we use to lower the flow temperatures of solder can make the ingots very brittle. This is true in most precious metal solders. With time and effort we were able to roll out sheet plumb solder.
We gave the initial test solders to a local trade shop jeweler, who faces a wide variety of assembly, sizing and repair jobs. His reports were extremely encouraging. We then began a wider series of tests, all based on real world circumstances. Many thanks to the local LA jewelers who tested and reported to us.
A month or so later, at Kraftwerks 1999, I set up a soldering bench with some scrap platinum jewelry and the brand new solders. This was a chance to ask the experts who were present at Kraftwerks that day to assess the new solder. Anyone who wished to try the solder was given the chance.
How to use the Solder
With time and testing we established approximate flow temperatures and found where we must be careful with how we use the solders. As was suspected, this solder requires no flux. The very high purity seems to take care of any problems in the alloy as far as oxidation goes. We found this solder must not be used like one uses gold solder. By that I mean that this solder is fairly viscous, unlike gold easy flow solders. The new platinum solder stays close to the joint.
All reports of discoloration have been heard from jewelers who pick this solder up as a molten ball with a titanium or tungsten pick. This would imply that those metals either alloy into or somehow discolor the solder. All this really means is that you must use some other way to place the solder at the joint. One trick is that red hot platinum is sticky by nature. Flux can disturb the surface finish, so is not suitable for keeping solder in place. With sizing there is no problem as long as you have enough tension in the joint to hold the slice of solder. One important advantage to the new solder is the superior color match at the lower flows. This allows one to melt the solder all the way through a shank without fear of melting the ring shank itself.
The present available formulations are as follows:
Pt-E is 90% Pt, and 10% alloy, and flows in the 1300°C range-Our "easy flow" solder. As the name implies this is our "easy flow" solder that is "plumb" (same content as the intended jewelry) to all the 90%Pt/10% Ir or Ru or whatever. Its color is closest to 90/10 of course. Pt-M is 92.5% platinum. The way to increase the flow temperature was to increase the platinum. This material flows in the 1400°C range. This is our "medium flow" solder. Its color works with any kind of platinum jewelry, but is only truly "plumb" to 90/10 jewelry.
Pt-H is 95% platinum. The highest flow among the new solders, it flows at 1500°C or a bit less. We call it the "hard flow" solder, despite the fact that its flow temperature is hundreds below the flow of ordinary casting platinum. It is "plumb" or better to all platinum jewelry. An ironic twist to this formula…. It may be a bit whiter than 90/10 jewelry. In certain items this can be an issue.
Easy, Medium, and Hard is one way to look at the solders. Another is to simply go by the Pt content and match whatever you are working on. That is ideal for color, and works fine when you only need one flow to do a repair. This solder is the closest color match simply due to matching the platinum content. . Scientific testing may show that our flow temps are a bit off. The tests we find most valuable are those performed by jewelers at their benches. After all, those are reality based. The physical strength of this solder is very high.
One will notice the solder sheets themselves are quite hard and springy. That is because they get so work-hardened during manufacture. The solder will not "polish out" leaving a seam. In rare instances, like when the newly soldered joint cools very slowly, some "ridging" can be found. Lightly abrading the ridge, then lightly burnishing around and on the joint, followed with normal polishing can easily address this. Another approach is to heat the item to annealing temperature and quench.
Plumb solder works well on all common platinum alloys. That includes Iridium, ruthenium, palladium, cobalt and copper. A possible exception may be the new lower flow temperature platinums such as Hoover & Strongs S+™. Due to the low melt of these casting and fabricating metals, the usual spread between the host platinum and our solder is reduced. By the way, I want to point out that all high temp solders have a potential problem with some platinum alloys-Simply based on the relatively low melt temperature.
Polishing platinum is a renowned challenge. A common frustration with repair platinum solder is the tendency to polish out and leave a seam. Plumb solder more closely matches the rest of the item. We have not yet developed a plumb platinum solder that flows at 1200 or less.
V8N5
Understanding Plumb Platinum™Solders
Daniel Ballard
Precious Metals West
This is an abbreviated version of the original work. For full technical details, please consult the original paper.