You can make solder for any metal that you work with, be it gold, silver, or other alloys. Even those that contain aluminum, lead, and tin…
For the silver/copper system, there is a eutectic point of 28% by weight of copper to silver.
This is the point where the alloy composition melts at the lowest temperature. You can make solder of any composition that will melt at a lower point than sterling. DO NOT use a eutectic alloy of copper and silver since it will be off color… Zinc and silver also have composition points which are even lower in melting temperature… adding zinc is difficult to control since zinc tends to burn off at its melting point…however, a zinc silver alloy will keep it’s bright color. Zinc/Silver/Copper alloys all melt at a lower temperature any of the pure metals alone… a three metal system will have ternary points rather than a single eutectic.
I know that this seems complicated, but you can google phase diagrams for two and three metal systems…start with at a two metal composition and google the phase diagram for it…with a two metal alloy system, you can vary the composition of the alloy to precisely match it’s melting point… that way you can make solder that will melt at different temperatures…with a two metal system, the eutectic point is always the lowest melting point… in the copper/silver system, at the 28 weight% copper eutectic, the melting point will be 1430 degrees F… moving towards either more copper or more silver will increase the melting point…move towards more silver, as too much copper will cause darkening of the alloy which is your solder…the melting point of pure silver is 1763 degrees, that of sterling is 1640 degrees F… sterling is .975 weight percent silver and .025 weight percent copper.,. if you are working with sterling, you can’t add more silver to lower the melting point… you would have to add more copper…more copper will give you a lower melting point solder, but you are limited by the amount of copper than can be added due to darkening of the color…the zinc/silver system is a lot more complicated… there is a 700 degree C melting point of an alloy of about 25W% zinc… adding more zinc progressively lowers the melting point…but there is no eutectic point in this system…
you can find these composition/phase (liquid, solid) diagrams for any alloy of any two or even three metals by googling them…there are so many alloys of gold that are of bi or tri metallic composition that making gold solder is both easy and difficult… difficult because the phase diagrams become so complicated… measuring the amount of alloying metal to lower the melting point of what your wish to make into solder has to be done precisely with a very accurate scale…some diagrams make it even harder as they give the percentages of metal by atom percent… you would have to convert that into weight by multiplying it by the atomic weight, not the atomic number…
After getting tired of paying for solders, I started to make my own, using the phase diagrams.
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