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Soldering and melting points


#1

I am curious about when exactly a solder should melt and flow in relation to the melt and flow point of the parent metal. It is the case for silver that the flow point of the solder is well below the solidus of sterling. Is this also the case for gold? Or does the liquidus of the solder match or exceed the solidus of the parent metal? Is this risky for melting the piece? If you have a 14K gold with a solidus of 800 degrees and liquidus of 840 can you use a solder with a flow point (liquidus) of 804 degrees?

To put it more simply, does the flow point of the solder have to remain below the solidus of the parent metal?


#2

If your flow point of solder matches or exceeds sterling silver or gold flow/melt temps you should not need solder. You would be fusing the metal.
Fusing metal occurs just below melt temp. Melting occurs at melt temp. There is a fine line.

Solder comes and can be made to flow at many flow temps.

If there is only one solder joint on your piece you can use any compatible solder for your metal type. For maximum strength I would use as high melt temp solder that I had available and that was compatible with my parent metal.

If you are assembling multiple pieces together in one piece you will want to start off with “Hard” solder and move to an “easy” solder as you assemble the work.
~You may also want to coat your finished solder joints with something to help prevent them from flowing as you move to the easy/lowTemp flow solders.

The flow point of the solder remains below the melt temp of the parent metal.

This chart link should help: https://www.riogrande.com/article?name=Selecting-Silver-Solder-CGl

Solder Flow Points Use for
Extra-hard 1490°F/810°C Laser welding, repair operations
Hard 1450°F/788°C First soldering operations
Medium 1360°F/738°C General soldering;
intermediate operations
Easy 1325°F/719°C General soldering and repairs;
intermediate or final operations
Extra-easy 1207°F/653°C Final soldering

More resources from Rio Grande: https://www.riogrande.com/category/resource-center/search-results?queryTerm=solder&tags=&contentTypes=&pageSize=32&categoryId=&page=1&searchType=1
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#3

What’s missing here is that each time you heat solder, the melting temperature rises. You can do pretty much any piece with one grade of solder - each time you make another joint, the prior joints have a higher melting temperature than the new one you are doing.


#4

Yes. The solder can change composition. This is due to alloys burning off.


#5

The solder doesn’t change composition and in many cases no part of the alloy burns off. Rather, the melted solder alloys with a small bit of the material being soldered to form a new alloy in the area of the join. This new alloy has a higher melting point than that of the solder used.

Thus, if soldering sterling silver parts with hard silver solder, the area of the join–after soldering–is an alloy of ‘hard-solder-plus-sterling’. Since there’s more silver in this alloy than in the original solder, it has a higher melting point. Each time the joint is heated, it combines with a bit more of the sterling, forming a new alloy and raising the melting point of the material in the area of the join.

I recently read an old post in the archives by Leonid Surpin referencing a type of ring he did with literally hundreds of solderings. He used only hard solder. :slightly_smiling_face:

Janet in Jerusalem


#6

Metal changes composition when an alloy burns off.
It is possible to use only hard solder on work that has multiple solders.

Janet, I think what you are referring to is what I would simplify into “The teeth that hold the solder in the joint”.

Found on page 414 of Jewelry Concepts and Technology by Oppi Untracht under the Fabrication Chapter & sub-title “The Soldering Operation”.
Oppi writes, “During the heating period prior to solder flow, the crystals of the metal in the parent object expand and grow, and minute spaces open between them which the solder fills when it flows. Therefore, a limited diffusion occurs between the solder and the parent metal at the contacting surfaces, forming a localized alloy which strengthen the bond. The degree of fusion varies with different metals and alloys, and with the solder composition.”

Debra


#7

Any/all of materials change if/when part of them is removed…:-)… My point was that in traditional gold alloys (Au/Ag/Cu), none of the three components burn off.

I knew Oppi-- some of my work is in that book…:-)… The particular description you have quoted is quite accurate.

Janet in Jerusalem


#8

Thank you Janet. That’s pretty special! I will look for your credits and work. Please give me a tip on how to find your work in her book.

Were you able to work or study with Oppi?

Jewelry Concepts and Technology by Oppi Untracht is full of knowledge.

Debra


#9

FWIW, Oppi was a he.
I met him once at a symposium at FIT. He was very nice to younger jewelers, a modest and gentlemanly fellow.


#10

I believe Oppi was more a historian/anthropologist of metal techniques than a practicing metalsmith (apart from some enameling on copper-- bowls and plates). His wife was a practicing artist in a number of media. In the 70’s I had written him in regard to black gold (which was pretty much unheard of in those days). He wrote back that it was impossible for there to be any such thing… I sent him some technical material from scientific gold journals and he duly apologized…:-)… From then on we maintained a correspondence… He contacted me in regard to my filigree work for the chapter on filigree in the book. You can see some photos of my work by looking up my name in the index: Janet Berg. The thing I remember most about him is that he was very interested in combs and had a large collection in different materials and techniques…:-)…

Janet in Jerusalem


#11

Janet,
Your interpretation of the Jewish ceremonial wedding ring has always been a favorite of mine and influenced some of my early work.
Thank you,
Debra