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Cleaner for Silver Soldering

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ChrisH25/02/2017 16:43:59
1018 forum posts
30 photos

I have to do a bit of silver soldering and don't have any citric acid to do the pre and post cleaning.

However, I do have some kettle descaler whose main ingredient is formic acid - if I remember the label correctly. So I was thinking of using a dollop of that with some very hot water and cleaning the parts in that.

Will that be OK?


Nick_G25/02/2017 17:08:20
1808 forum posts
744 photos


Have you got an Asian food shop close to you.? (That's Asian food, not owned by) They are usually open late.

2 I know of in Warrington both sell quite big bags of citric acid crystals for a couple of quid. - No idea what they use it for.






Edited By Nick_G on 25/02/2017 17:12:42

Peter Layfield25/02/2017 17:18:30
37 forum posts

would it also clean mild steel prior to soft soldering, or what would clean rusty m.s.?

Rik Shaw25/02/2017 18:34:19
1480 forum posts
398 photos

Peter - for rusty steel I use cheapo malt vinegar. About 26p a bottle for the "value" stuff last time I looked. Chuck your stuff in and check after 24 hours. When it looks good and black wire brush it, rinse with boiling water - it will dry in seconds - then lube to stop it going home again. Thats the way I do it.


Neil Wyatt25/02/2017 19:42:24
18992 forum posts
734 photos
80 articles

All the weaker acids - formic, citric, phosphoric, phosphonic, acetic will work fine as a pickle or as a rust remover. They don't work as fast as strong acids, but they are much safer and more pleasant to handle.

In simple terms, if they are strong enough to fizz limescale, they will do the job.

Andy Ash26/02/2017 00:10:02
136 forum posts
33 photos

Citric acid can be pretty potent if you heat it up.

Below is a link to a paper showing how citric relates to other acids.


The tests describe weight loss in standardised steel test subjects at different concentrations and temperatures.

At room temperature citric is so benign and in any case cheap, I don't really understand why one would use anything else for small parts fabrication. With large objects like whole boilers it is different, I accept that up front.

If you get citric nice and hot, you can dunk a small steel silver soldered assembly into the acid and see the oxide layer just "pop off" in just a few minutes. It is literally left floating in the acid like a lizard shedding it's skin.

I use a stainless pan I bought in Sainsburys. I have a temperature controlled hotplate and a thermocouple inside an Inconel shell suspended in the acid by a spider. The thermocouple allows the hotplate to directly control the temperature of the acid.

I made the acid up using de-ionised water (for lead acid batteries) and I bought industrial cooking citric acid granules, from e-bay. The first batch I actually made on the kitchen cooker, and I just kept stirring the granules in until no more would dissolve.

I regularly filter the acid into a plastic container for storage, with Rombouts coffee percolator filters. You lose water by evaporation, so I just top it up each time I use it with the DI water. I originally made my current pickle about two years ago, and it still works nicely now.

I typically use it at around 65-70deg C.

The thing I like about citric is that it does the job. When it is cold even if you spill the whole thing, the only problem you have is a sticky mess that you have to clear up.

Watch out when it's hot though!

Edited By Andy Ash on 26/02/2017 00:15:09

ChrisH27/02/2017 11:05:29
1018 forum posts
30 photos

Sorry for the delay in response - have been "laid low" for a couple of days, but thanks for all the replies.

Neil many thanks for your reply, that was precisely the answer I was hoping for!


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