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Old 06-10-2012, 06:50 PM   #1
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Borax

Hey, Is "20 Mule Team" laundry borax the same as what we'd use for melting silver at home?
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Old 06-11-2012, 08:30 AM   #2
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As far as I can tell, 20 Mule Team is 100% sodium tetraborate:

http://www.20muleteamlaundry.com/about

http://en.wikipedia.org/wiki/Borax
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Old 06-11-2012, 08:34 AM   #3
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Yup, it's pretty pure. Most fluxes add some boric acid (available as ant killer) too, the net melting point of the combo is a little less. Regular borax has ten "waters of crystallization" so you have to heat it kind of slowly or it "boils" that stuff out (messy) too fast.

Neither is a "reducing" agent. What they do is prevent oxidation to the extent they cover the melt, but also dissolve already-oxide kinds of things. If your metal was already part-oxidized, that part will wind up dissolved in your flux (and, in general, lost).

I have a bunch here to use as a slow neutron stopper - the stuff absorbs neutrons quite well compared to most other (affordable) things.
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Old 06-12-2012, 07:04 AM   #4
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Originally Posted by PMBug View Post:
As far as I can tell, 20 Mule Team is 100% sodium tetraborate:

http://www.20muleteamlaundry.com/about

http://en.wikipedia.org/wiki/Borax
So I imagine if I were to melt some small qtys of junk silver, I could just go purchase "20 Mule Team" borax at my local A&P to use as the flux, rather than ordering something off e-Bay?
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Old 06-12-2012, 07:14 AM   #5
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Sorry, I've never had the desire to melt any silver, so I don't know anything about doing that. DCFusor is the resident expert in physics and chemistry.
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Old 06-12-2012, 07:55 AM   #6
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I'm not (yet) expert in casting silver, but I've got the stuff to try with, so I might do it and report. I use borax as a flux for my bullet casting (or in mixture with boric acid).
I also use it in silver soldering and brazing. Flux for that process will definitely work well. If you can't find it at the hardware or welding store, McMaster-Carr has everything and is a good outfit to deal with. http://www.mcmaster.com/#
They have so much stuff you just about have to use the search function. Their catalog is 4" thick - on bible paper.

A general problem with hot metals is surface area/volume ratio. Small amounts are harder than large amounts, because they have more surface area to oxidize compared to the total amount - thus the percentage losses are greater.

I have a huge box of worn out keyboards (you can guess why) and am planning to strip them and melt them, though, just to play with the idea. This was mentioned here elsewhere, but rather than chemically remove the silver with acid and making silver nitrate, I plan to just use a solvent and scraper and leave it as metallic dust mixed with a bit of plastic. As I heat it, the plastic will decompose and mostly leave carbon which is a reducing agent itself, and I shouldn't have to put borax on it till we get pretty hot - but that's what I'm going to find out.

For extreme cases, I have a Vulcan heat treatment oven, programmable, I can just fill with inert atmosphere (say, argon) to do this - it will go to about 1000C. In that case, no flux is required.

I can also make my own crucibles out of various things - quartz or pure carbon, for hi temp work. In the case of quartz, I can custom-make something I can again control the atmosphere in - for example, pull a vacuum on it, again eliminating oxidation losses. Or use a hydrogen fill to reduce any silver compounds back to pure silver at high heat.
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Old 06-12-2012, 09:16 AM   #7
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Well, I was really just interested in the occasional "junk" silver melt. I've got a crucible and will more than likely get a MAPP gas set-up (can use that for my automotive purposes, too) just in case I somehow acquire some sterling. I found 3 old sterling rings last night that neither my wife or I have worn in 20 plus years and was gonna melt them just for the heck of it. Make a little disk and stamp it ".925". Was just curious if I needed to toss some borax in there, and then where'd be the best place to purchase the borax.
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Old 06-12-2012, 03:23 PM   #8
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Yes, go ahead and bury it in borax before you even heat it up. If it bubbles a lot, slow down some and wait for that to stop before going with more heat.
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