cleaning metal after silver soldering

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LiamO'Flynn
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Joined: Sun Mar 08, 2009 12:53 pm

cleaning metal after silver soldering

Post by LiamO'Flynn » Thu Sep 20, 2012 6:03 am

I find it very difficult to remove the caked on flux aftering soldering ,i have been useing a sodium bisulfate pickling solution to remove most of the flux but it discolours the metal (nickle silver) which means alot of work cleaning the metal afterwards.
Do you use a different method or do you have any tips to make the process less work, thanks

Liam
Liam O'Flynn the plumber not the piper .

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DMQuinn
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Location: Finger Lakes

Re: cleaning metal after silver soldering

Post by DMQuinn » Fri Sep 21, 2012 6:12 am

Can you say more about the nature of the discoloration you're getting?

LiamO'Flynn
Posts: 149
Joined: Sun Mar 08, 2009 12:53 pm

Re: cleaning metal after silver soldering

Post by LiamO'Flynn » Fri Sep 21, 2012 8:03 am

Heres a photo taken after some cleaning has already been done. I can clean the discolouration that you see but it takes alot of time and effort ,So can that type of discolouration be avoided or how would you clean it also if you dont mind Mr Quinn ,what your soldering and cleaning methods?
Thanks, Liam
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Liam O'Flynn the plumber not the piper .

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DMQuinn
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Re: cleaning metal after silver soldering

Post by DMQuinn » Sat Sep 22, 2012 9:41 am

Thanks for posting the picture. (Nice looking tubing, by the way.)

I think what you have there is oxidation discoloration, and while it is on the surface, it is not infinitely thin. Whether you remove it chemically or mechanically, you’re going to have to spend some time re-establishing the surface, which is what happens when you apply abrasives, either sandpaper or polishing compound.

If you look carefully at the stains, you’ll see some fairly well defined edges, and I presume that where you have an otherwise bright area contiguous with a stained area, what you’re seeing is the edge of coverage by your flux, which would have covered the bright area while you were applying heat for soldering. Where the metal was not covered by the molten flux is where you’ll see the heaviest oxidation.

Although some have warned here against the use of acid pickle, that’s what I use. I used to use a pickle made up from a commercially available mix called Sparex, the basis of which was/is, I believe, the same chemical you mentioned, sodium bisulfate. I used it for years, but never felt comfortable with a means of disposing of the spent liquid. Perhaps ten years ago or so I started using citric acid, something I can get at a local grocery store in the canning department. This works quite well in a fairly weak solution (perhaps three ounces of crystals to a gallon of water) and does a good job of dissolving the remaining flux glass and removing oxidation coloring. I keep it in a large crock pot which I turn on only when I need to use it, to make the solution hot. Depending on how fresh the solution is, the length of time a soldered piece spends soaking in the pickle will vary from as little as 10 minutes to as much as a couple of hours. The acid will eat away at the surface of the metal as well as the remnants of the flux, and over the years I have ruined a few pieces by forgetting about them in the pickle overnight. If a piece remains in the warm solution too long, the surface can degrade considerably, so you have to watch things carefully. Pickling solutions can be used cold, but they work better and faster if they are warm.

When a piece comes out of the pickling solution, it will generally have a dull matte appearance, but it doesn’t have the dark stains as seen in your photo, so the citric acid will indeed remove the dark stains that are bothering you. I would expect a piece soaked in a Sparex solution to come out looking exactly the same way, so my guess is that a longer time in the pickle would have taken these stains away, but perhaps at the cost of a little of the smoothness and reflectivity your piece shows.

It is essential that pieces which have been pickled in acid be rinsed and brushed very thoroughly, preferably under running water, to remove all traces of the acid, inside and out. So far I have not seen any damage or degradation that I can attribute to the citric acid pickle, and as I mentioned, I have been using it for something like yen years now. Still, with the matte finish, I expect to spend a good bit of time with each piece after the soldering has been done, to remove any excess solder that may have flowed where it is not wanted (the left leg of the assembly in your picture shows what I’m talking about) and to re-establish a fine surface that can be buffed and polished. This is done with files, abrasive papers and elbow grease. So you can perhaps reduce the amount of work you’d have to do to remove the stains by using a chemical pickle, but it will not eliminate the need for handwork. Something for nothing you don’t get.

You asked about my soldering and cleaning techniques. I don’t do anything outside the ordinary standard operating procedure for silver soldering: achieve a good mechanical fit, keep the surfaces of the joint scrupulously clean, apply a flux appropriate for the metal and solder, and heat the pieces to be soldered only enough to allow the solder to flow into the entire joint. Any of the many books on metalworking, and in particular on jewelry making, will give sound directions on how to achieve good silver solder joints. Clean up, for me, begins with pickling in a weak citric solution followed by thorough rinsing and re-establishing the surface around the joint. Nothing special, but there is a good bit of work that goes into it.

LiamO'Flynn
Posts: 149
Joined: Sun Mar 08, 2009 12:53 pm

Re: cleaning metal after silver soldering

Post by LiamO'Flynn » Mon Sep 24, 2012 2:54 pm

I think I'll give the citric acid a go as I think the sodium bisulfate is more trouble than it worth, not least that it attacks the body of the Crock pot(slow cooker) very quickly. Does this happen with the citric acid?
One thing I also discovered is that you really need to clean the piece afterwards or else the acid continues to work on the metal and forms some kind of crystals on the metal . To be sure I soak the work in baking soda solution to neutralise the acid.
To be honest I was hopeing there was some lazy was of getting spotlessly clean metal without the application of elbow grease, Ah well no such luck

Thanks Mr Quinn for your response
Liam
Liam O'Flynn the plumber not the piper .

outofthebox
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Re: cleaning metal after silver soldering

Post by outofthebox » Tue Sep 25, 2012 4:24 am

I remember reading on some other forum that someone recommended using tippex (the white typewriter correction fluid) when soldering. He painted it on the metal surface where he didn't want the flux to flow. Then it was easy to clean off afterwards. I've no idea if this would work for you - but I thought I'd pass it on here and you might like to experiment with it - and let us know if it works.

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