For example, the 14K alloy you mentioned has a solidus point of around 800 degrees according to my phase diagram. Most hard 14K solders flow around 800 degrees also. One should have a while before the solidus point of the metal you are soldering is reached. Unless I am mistaken and the liquidus of the solder should not be the same as the solidus of the parent metal. I always thought the solder should flow before the solidus of the patent metal is reached.
Zinc with a melting point of 419C (786F) is frequently added to create gold solder alloys, be they yellow or white. Zinc is a great suppressor of melting ranges of karat golds.
“And it’s not clear why you would think zinc prevents copper from oxidizing…”
The reason being (1) zinc oxidizes preferentially protecting/preventing the copper from oxidizing and (2) unlike copper oxide which is solid at the alloy processing temperatures, zinc tends to vaporize and its oxide usually does not mix into the molten metal.
This post has essentially turned into a “zinc vs no zinc”
Debate for gold alloys. I LOVE IT. I was so confused on whether to put zinc in my gold and there is very little info on the topic elsewhere.
“I was so confused on whether to put zinc in my gold and there is very little info on the topic elsewhere.”
Jonah, the article by McDonald and Sistare that you shared with us has tons of information on role of zinc addition to karat gold alloys!!
Exactly! And that’s about it.
I typed “zinc” in the search box and found references to role of zinc by Peter Rowe, Jim Binnion and others…
Maybe I haven’t been looking in the right places but when I have looked far and wide and haven’t found a ton on the topic of zinc free golds.
We at Stuller make a single zinc-free 14KY gold alloy to make laser wire. People knowledgeable in laser welding tell us zinc free version fuses better with no interference by zinc fumes when hit with laser.
All other karat gold alloys we make, yellow, white, rose, green contain zinc!
Do you think I should include zinc in my 14K yellow? If so how much?
Amount of zinc you want to put in 14K yellow depends on amounts of silver and copper. All 3 will determine the color of yellow gold you want to achieve. Stuller 14K yellow golds contain anywhere from 4 to 8%. Higher the zinc, paler the yellow color, like euro yellow or yellow with touch of green.
Does zinc lower or raise melting temperature? Might I getaway with a solder with a flow point of 804 degrees?
Hi Shan!
Julie
As I mentioned before in this thread, additions of zinc lowers meting range of yellow gold, all else being equal.
If you are opting to use a solder that has a flow point of 804C (1479F), I’d suggest you go for a gold alloy that has high copper, low silver and low zinc, in order to keep the karated gold from softening before solder flows. A good rule of thumb is to choose a yellow gold formulation that has a solidus at least 50C (90F) above the flow point of solder you plan to use. It is not impossible to work with an yellow gold alloy that has a lower solidus, it depends on the type of soldering job and the skill of the goldsmith.
Ah thank you. I just made up some master alloy that is 75% Copper, 15% Zn and 10% Silver. It should work as it is high copper low silver and relatively low zinc.
When I first started out I was real into colored golds and collected formulas from old and ancient sources. Out of well over 50 formulas covering yellow gold, red gold, green gold, gray gold, white gold, blue gold, purple gold, and brown gold, only two contained zinc. Both were for 18 karat white gold. Most of my formulas are from turn of the century resources and from the first half of the 1900s. You might want to think about why no traditional goldsmiths used zinc in their alloys…:-)… In any case, we know it’s possible to make all the beautiful gold artifacts you seen in museums without zinc…
Janet in Jerusalem
I might do that aswell. I am gathering formulas, making master alloys, I might use it I might not? I might have to make my own solder, or use a medium rather than hard if I use 14K yellow without zinc as the melting point is rather low for a solder that flows at 804 degrees.
Actually, do you think I could get away with a higher copper content and no zinc, or would the colour be too reddish? Maybe 28-29 percent copper, 12.5-13.5 percent silver? I don’t want to make up the alloy and find it too rosy for my liking…
If the zinc vaporizes, how do zinc oxides prevent copper from oxidizing?
Janet in Jerusalem
Zinc acts as sacrificial element if present in the molten karat gold because it has greater affinity for oxygen than either copper or silver. So, it prevents copper and silver from oxidizing.
If zinc vapor exists over the molten gold alloy, it could prevent oxygen from getting to the molten metal. In practice, a better solution to prevent molten metal from oxidizing is the use of boric oxide flux cover.
Zinc oxide, once formed,will not prevent copper from oxidizing.