recycled silver tarnishing at a faster rate

[joyerico]

Hello,

I have a lot of silver 925 to recycle myself ... i'm taking about pounds and pounds from processing lots of orders ... I use a crucible and a oxy-torch for melting it and then make sheets of the appropiate gauge with my rolling mill. Some borax is poured on the crucible to help into the process.

HOWEVER

i have observed that the silver i got from this process tarnishes faster than the 925 silver i buy from providers ... And i don't understand why... This is really annoying, given i can only use this scrap silver for making samples or oxidized jewelry. And the alloy is exactly the same: 925 scraps put on the crucible and melted.

Do you know why this could happen? How can i fix it?

My guess is that the metal is not well melted and copper doesn't re-mix well with silver in the crucible. Just a gues. No idea :(

Thx.

[theresa]

Have you tried adding fine silver to it? I had the same problem but adding the fine silver made it less so.

[joyerico]

Thank you very much, Theresa. I think that will fix the problem.

And how much do you add, more or less?

[MMM Jewellery]

A few things come to mind- are you scrupulous about not adding in soldered joins? If not the extra impurities from the solder will not help things. Secondly, molten silver has a very high capacity for absorbing oxygen so adding powdered charcoal to absorb the oxygen might help (short of getting a controlled atmosphere furnace!). Lastly the crystal structure of the poured bar will be unoptimal and so lead to surface defects on working- it pays to forge the bar with a hammer before rolling as this breaks up the crystal structure to finer grains.

[Dennis]

it pays to forge the bar with a hammer before rolling as this breaks up the crystal structure to finer grains.

From http://www.totalmateria.com/page.aspx?ID=CheckArticle&site=kts&NM=277

Forging results in metal that is stronger than cast or machined metal parts. This stems from the grain flow caused through forging. As the metal is pounded the grains deform to follow the shape of the part, thus the grains are unbroken throughout the part. Some modern parts take advantage of this for a high strength-to-weight ratio. Dennis.

[MMM Jewellery]

You are perfectly right Dennis! Sorry, I should have said forging followed by annealing

[joyerico]

Thank you very much to you all ...

I will try adding some charcoal power,and also some .999 silver. Guess both will be enough.

Regarding small soldering on the pieces to melt, yes, they may be a bit... Bot i use to melt more or les 30 grams each time, and it would be a very low amount, so it doesn't look like having too much influence. Anyway, will be more careful with this too.