Metal loss while melting

purplepepper8

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Joined
Sep 19, 2019
Messages
27
Location
India
Hey, so far i have been getting alloyed gold sheets from another jeweller but figured now id start doing it myself. before trying with gold, i decided to practice with sterling silver (925 silver) since i haven’t done this before. each time i remelted the silver the weight would be around 2-3% less. i was wondering if this is normal? I found some tiny balls of silver stuck in the boric acid that coats the crucible (but the amount of that didn’t increase which each melt so the loss isn’t necessarily all getting stuck in the boric acid). Do some tiny bits fly out of the bowl with the force of the torch or get lost elsewhere? and wanted to ask if i should expect any loss with gold as well?
Lastly, how important is it to add boric acid powder while melting the metal?
FYI i am using the melting tip on the smith little torch and not a furnace.
Thanks :)
 
Last edited:

Sinterklaas

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Dec 19, 2015
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Holland
Some loss is expected. I never weight it. But 2-3% is a lot. If your trouble is the small balls blowing away. Melt big parts first then throw in the small stuff.
Make sure your not overheating the melt. It will cause metal to evaporate! Always use proper ventilation.

Boric I would coat the crucible. That is only a 1 time thing when you get a new crucible. Then with each melt I add some when it is molten.

I dont think you should have this much loss. But again I never measured it.
One last tip you can also have a half bowl on top of your bottom one if you use the square crucible.

I found this:

And if you get this type you can cut 1 in half and us it as a lid.
 

purplepepper8

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Sep 19, 2019
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27
Location
India
Thanks for this info Sinterklaas :) and appreciate you taking the time to respond. the covering idea is good, i’ll try that. and i’ll try to not overheat, although will have to learn what that means
 

Sinterklaas

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Dec 19, 2015
Messages
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Location
Holland
Overheating will give more green to your flame when melting an alloy containing copper. It is the copper burning away. Little bit of green is not a reason to worry.

Just start your melt and when you see all is about to become 1 molten blob. You can see it it is like a crust layer on molten metal. Then remove your flame, add some boric powder. And start to heat again. When you see the crust layer peel away. And the melt becomes shiny that is when you pour. When it is shiny you can swirl it softly around in your crucible to check if it is 100% liquid. The longer you keep heating after the melt has become 100% liquid and shiny. The worse results will be. I suspect more loss , but also your quality will suffer.

Is your alloy dry when you weigh it? Maybe some weightloss can be explained is you have some wet silver/copper. Then the water will obviously evaporate.
 

purplepepper8

Member
Joined
Sep 19, 2019
Messages
27
Location
India
Overheating will give more green to your flame when melting an alloy containing copper. It is the copper burning away. Little bit of green is not a reason to worry.

Just start your melt and when you see all is about to become 1 molten blob. You can see it it is like a crust layer on molten metal. Then remove your flame, add some boric powder. And start to heat again. When you see the crust layer peel away. And the melt becomes shiny that is when you pour. When it is shiny you can swirl it softly around in your crucible to check if it is 100% liquid. The longer you keep heating after the melt has become 100% liquid and shiny. The worse results will be. I suspect more loss , but also your quality will suffer.

Is your alloy dry when you weigh it? Maybe some weightloss can be explained is you have some wet silver/copper. Then the water will obviously evaporate.
good to know thanks. i was seeing plenty of green so i’ll try to act faster. and thanks for the timing on adding the boric powder.
yes it is dry.
but as an update i did melt a few more times and my losses came down significantly- around 0.4-0.5%
 

rweigel

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Joined
Dec 22, 2017
Messages
72
Location
France (north of Alsace, close to Germany)
I experienced comparable weight losses while melting silver when I replaced my broken air-propane torch by a small oxygen-propane torch. To get enough heat (BTU, not temperature) from the small torch I turned the gases to high flow. As a result, I agitated the molten silver a lot by the high pressure flame and got weight loss, sometimes hazy air in the shop and for good measure brittle silver which tended to crack in the final steps of a jewelry piece. After I bought another air-propane torch with a big nozzle and a big flame, everything turned back to normal. My conclusion: for melting with the open flame in a crucible, use a big flame with low oxygen content and low pressure. 3000°C will do no good here.

Cheers

Ralf
 

silvermon

Member
Joined
Mar 26, 2014
Messages
52
Location
Davenport, Iowa
Hey, so far i have been getting alloyed gold sheets from another jeweller but figured now id start doing it myself. before trying with gold, i decided to practice with sterling silver (925 silver) since i haven’t done this before. each time i remelted the silver the weight would be around 2-3% less. i was wondering if this is normal? I found some tiny balls of silver stuck in the boric acid that coats the crucible (but the amount of that didn’t increase which each melt so the loss isn’t necessarily all getting stuck in the boric acid). Do some tiny bits fly out of the bowl with the force of the torch or get lost elsewhere? and wanted to ask if i should expect any loss with gold as well?
Lastly, how important is it to add boric acid powder while melting the metal?
FYI i am using the melting tip on the smith little torch and not a furnace.
Thanks :)
A lot depends on the alloy you are using. Some metals in sterling alloy are there specifically to vaporize and de-ox the ingot. Zinc is one such metal (common more often in the past), but there are many. If you keep remelting the same sterling, the quality of any sheet you try to roll out will be reduced by the increase in oxygen absorption, and the presence of small amounts of carbides. Pure silver in the liquid state has a high affinity for oxygen, and somewhat for sulfur. Copper is much the same.
 

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