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Author Topic: tumbling silver chain  (Read 1755 times)
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ajda
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« on: February 03, 2015, 03:53:56 AM »

Here's a question for MizGeorge and other silversmiths out there... Using a rotary tumbler with steel shot for burnishing causes silver chains to get horribly tangled up. I've come across some possible solutions, such as threading the chain onto a length of wire... What would you recommend?
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mizgeorge
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Or should that be missus?


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« Reply #1 on: February 03, 2015, 04:00:51 AM »

 It's funny - I hear about this problem from time to time, but have never experienced it. Perhaps because I only really make and use fairly heavy chains.

I actually think it's probably easier not to tumble finer chains, but to just clean them up with some silver dip. Otherwise, yes, threading onto wire or elastic would do the trick. I think it's better to keep them fastened closed as well.
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ruth
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« Reply #2 on: February 03, 2015, 06:15:44 AM »

You can also tumble a chain in a sealed plastic bag but silver dip is more effective and quicker.
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ajda
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« Reply #3 on: February 04, 2015, 04:01:04 AM »

Thanks for the input, both of you.

I've also found that heavier chain that I've made myself is OK. But I'm incorporating some lengths of factory-made finer chain with pieces that I've made and would like to tumble the whole once its all joined up.

It's Argentium 960 - my final steps are normally:
1 - heat treating for hardness
2 - tumbling to clean, polish and neutralise surface
3 - heat treating for surface passivation

This is a regime that seems to work very well, so I don't really want to change it - in particular, I don't want to use dip or bring the silver into contact with anything that might interfere with the passivation process. I'll try the wire trick... a bit fiddly perhaps, but maybe the simplest answer...

Ruth, I don't understand how tumbling in a bag would work - am I missing something? Perhaps for work-hardening, but not for cleaning/polishing?

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ruth
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« Reply #4 on: February 04, 2015, 05:33:47 AM »

Hi Alan, It is not logical is it? But it does work to a lesser degree than exposure to the shot. Takes a while.

What is passivation?
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ajda
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« Reply #5 on: February 04, 2015, 06:53:22 AM »

Hi Alan, It is not logical is it? But it does work to a lesser degree than exposure to the shot. Takes a while.
That's intriguing - I'll have to try it!

What is passivation?
Quoting Wikipedia: Passivation, in physical chemistry and engineering, refers to a material becoming "passive," that is, being less affected by environmental factors such as air and water. Passivation involves a shielding outer-layer of base material, which can be applied as a microcoating, or which occurs spontaneously in nature. As a technique, passivation is the use of a light coat of a protective material, such as metal oxide, to create a shell against corrosion.

Argentium silver differs from sterling in that some of the copper is replaced by germanium. Passivation occurs when germanium oxide forms a protective surface layer that prevents oxidisation of the silver/copper beneath - and this is why Argentium doesn't tarnish like sterling or fine silver. It happens naturally over time, but can be accelerated by a simple heat treatment, putting the finished piece in an oven or kiln at 100C for several hours.
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ruth
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« Reply #6 on: February 04, 2015, 07:51:11 AM »

So the germanium rises to the surface with time or heat?
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ajda
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« Reply #7 on: February 04, 2015, 10:08:51 AM »

I can't claim to be an expert on the chemistry/physics of Argentium, but I think that's more-or-less right. As far as I understand it the action of heating is twofold. First, it increases the movement of germanium atoms within the alloy so more of them find their way to the surface more quickly where they react with oxygen to form the invisible passive layer. Second, heating speeds up that germanium + oxygen reaction.
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