Getting rid of red flux stains on brass

[Brian Rupnow]

Whenever I silver solder brass parts, I use a paste flux recommended by the silver solder manufacturer.It is made by Harris, and is simply called "StaySilv white brazing flux". It works great but wherever it melts and runs to as a result of heat from the torch, which liquifies it, it stains the brass red. Not a vivid dark red, but still red enough to be quite visible. The attached picture shows two test parts immediately after silver soldering them together, and the reddish color around the soldered area is quite visible.

 

[Brian Rupnow]

Yesterday, I read on the internet that making up a cup of white vinegar and a teaspoon of salt, then heating it would yield a solution that, along with "brisk scrubbing" would remove the red stain. This is the result after a half hour soak. Although the parts are undoubtedly cleaner, the red stain is not removed, in fact doesn't seem to be affected at all.--Okay, so much for internet solutions!!!

 

[kquiggle]

Maybe not directly applicable to your problem, but I have had good results cleaning brass using Brasso metal polish applied with fine steel wool and a bit of elbow grease. Might be worth a try.

 

[goldstar31]

Brian,
This is no more than using 'Brown Sauce'. Seriously! Chemically it is acetic acid and sodium chloride and the last bit is- well, dipping in the sea.

You know that there is a lot of hot air about fluxes and quite often no more than borax and a drop of washingup liquid is needed.

So I would suggest that you use battery acid which is sulphuric acid which has already been safely diluted from concentrated stuff.

OK, having said safely, it is still pretty corrosive but it is the traditional 'pickle' used by model boilermakers. Rubber gloves, goggles and old clothes. If you feel a bit 'windy', you could try drain cleaner which is esentially Hydrochloric Acid or which some call Muriatic Acid.

Both jallops works but -be careful, please

Regards

Norman

Can I add a bit from my wife who was probably the best silver solderer that I ever married( hides)

To limit the spread of silver solder, go round the job with a B or HB pencil.

 

[t.l.a.r. eng]

I always use a 75% muriatic acid to 25 % water solution for pickling solder joints, it works amazingly well. Soaking the parts in this solution for 1/2 hr or so cleans all the nooks and crevices. Even removes rust from ferrous metals. I normally use the muriatic acid solution found at lumber warehouses mixed for cleaning pools and concrete.

Remember to allways add acid to water, not water to acid.

 

[goldstar31]

Remember to allways add acid to water, not water to acid.

This is for Sulphuric( H2SO4) not Hydrochloric( HCl).

Cheers

Norman

 

[fpravenscroft]

citric acid will also work you can get it from home brew paces or a good chemist not as volatile as sulphuric acid
regards
peter

 

[canadianhorsepower]

read on the internet that making up a cup of white vinegar and a teaspoon of salt, then heating it would yield a solution that, along with "brisk scrubbing" would remove the red stain. This is the result after a half hour soak. Although the parts are undoubtedly cleaner, the red stain is not removed, in fact doesn't seem to be affected at all.--Okay, so much for internet solutions!!!

Brian this method is use to remove flux residue and not the read mark you are talking about
I personaly use Past sylver in a seringe from Princess Auto and a Hot Air torch and I have no problem.
It does melt at half the temperature and the material will sheer before the solder brake apart
thats good enought for me
Luc

 

[Blogwitch]

You will be very lucky to remove the red stain with any chemical concoctions as it is usually fused into the surface layer of the piece part, a chemical reaction caused by flux and heat that brings a tiny amount of copper from the brass to the surface to allow better bonding. It needs to be removed by physical means.
I get rid of it very easily by using a brass brush wheel on my buffing machine, but for smaller items, one of the brass Dremel brushes also works well. With a bit of elbow work, you could also use wire wool, but it might take some time.

John

 

[Swifty]

To remove the flux residue, I'm another one that uses citric acid, easily available in the cooking section at the local supermarkets. I just mix some up in a container with some water, I reuse it until it seems to slow down and get very discoloured, then I just mix up another batch. No protective clothing or gloves required.

As far as the red tinge goes, I try to buff it off if I can.

Paul.

 

[crueby]

From the articles I have read (assuming they are true, I dont know for sure), some of the color change is due to the flux leaching a little of one of the metals in the alloy out, causing the color change. This is just on the very surface, so any polishing paste, or filing, gets you down to fresh metal without the color change. With all the silver soldering I've been doing on my locomotive project, that seems to bear out. Fortunately for that project most everything will be painted so the color was not a problem. After pickling (I am using a milder pickle solution called Sparex I got from a jewelery tool supplier - comes in powder form you mix in water to make a gallon, it is easier on skin than sulfuric by a long ways and does a nice job) for about 10 minutes or so, I brush with a wire brush to remove any remaining residue. That usually gives a nice bright clean surface, but some of that color change remains. Filing or abrasive pad usually removes that if needed.

 

[canadianhorsepower]

Hi Brian
I found this link pretty interesting and might solve your issue.
This guy is an copper art worker and he descripe how to create different shade
of red. If I understood this properly you are applying to much heat. any way linsten
to the video, if it helps good for you

[ame]https://www.youtube.com/watch?v=Y8qBu7Gq8yw[/ame]

 

[RonGinger]

I have tried both sulfuric and hydrochloric acids. Both cause horrible rust problems all over the shop. Just opening the bottle lets enough fumes out that a day or so later lots of your steel parts, like nice shiny handwheels or mill tables, will have the lightest sheen of rust on them. I dont want the stuff in my shop.

I have heard of citric acid but have never been able to find any of it. Years ago I bought a can of Sparex at the NAMES show, which does work great but I eventually used it all. I need to remember to order some when i have other items to order.

 

[goldstar31]

I'm or was a Certified Welder, double Distinctions City and Guilds and all that jazz. I assumed that this 'red' was a by- product of the flux. If it is actually Free Copper then it suggests to me that this is a low grade silver solder or that there has been too much heat and the silver solder( an alloy) is breaking up to its constituent metals.

OK, I can/could braze on sheet steel- C &G Motor Vehicle Restoration and expect to find a brassy finish on the joint if I use a borax flux and when I have been using silver solder, I expected and got a ring or seam of bright silvery join. Now I normally used a very neutral to a bit of a soft flame with an oxy/acetylene set. And I leaded the joints using the gas nozzle after 'tinning' with high tin solder paste before the lead was pushed onto the joint and depressions.

In silver soldering, I would wait for the wet flux to go molten and literally put a tiny piece of solder well fluxed into the join- and lift off- whilst the molten solder had just joined by capillary action.

I now simply wonder what differences exist nut that was and is my take.
regards


Norman

I'm a poor typist and my reply was without seeing the coppersmith video.

And I'd be wearing green goggles , gloves and safety clothes

 

[goldstar31]

I've just been visiting my favourite site( sorry but) and it is Model Engineering Clearing House.

Quite an interesting posting on 'rust' which is containing quite an erudite discussion on fluxes and things.

Maybe a visit, eh?

Norman

 

[Nerdz]

I know I replied to this. The forum ate my post. I use vinegar and salt, Ive tried a paste of baking soda and water. Ive also used toilet bowl cleaner (make sure it says it contains hydrogen chloride-this is Hydrochloric acid!) with some luck. HCl and Salt wont do anything (They will just exchange ions..). You basically want to get rid of an oxide (which is what that red stuff it-Its probably Copper Oxide I). Basic chemistry suggests that you need a Acid or Base to change it.

Side note: Red Copper oxide is actually a semiconductor and when exposed to light will produce a small current.

With that said, theres a few things I wouldn't mix. Never mix bleach and vinegar, or bleach and hydrogen peroxide. Both give off nasty chlorine or chloroform gas that linger.

 

[MCRIPPPer]

thats normal when soldeing brass or other copper aloys. the jewelers method of getting rid of it is to take some used pickle, and add some hydrogen peroxide. the oxygen turns the raw copper(the red stuff) into a copper oxide which is something that the pickle can remove. pickle cant take off non oxidized metal.

 

[Brian Rupnow]

Okay---it's experiment time. I have been assured by a forum member that he has good results by using citric acid. Since I am a bit too chicken to mess with sulphuric or hydrochloric acid, we will give citric acid a shot. Good wife went out shopping today, so I asked her to buy me a small bit of Citric acid at the natural food store. It comes in dry crystalline form, and looks exactly like table salt. The test vessel is a 414 mll pepsi bottle (Thats about 14 ounces to North Americans) I have absolutely no idea of the proportions to mix this stuff in, so we will start with 3 level teaspoons of Citric acid mixed with half a bottle of water. I will submerge the two soldered test pieces in the mixture and see what happens.

 

[MCRIPPPer]

citric acid is what we use as jewelry pickle. you have to add H2O2 to make it eat the coper color off.

 

[Cogsy]

When I was a hot dip galvaniser I pickled thousands of tons of steel in HCl, which was strong enough to eat the steel away if left in too long. (Interestringly, if left way too long, most steel starts to resemble wood with long 'grain' running through it). Of all the accidents we had in the place, I don't recall anyone ever having an issue with the HCl, despite being splashed with it every day and absorbing it through the skin.

My wife hated the job as I would sweat the stuff out and our sheets and pillows quickly turned yellowy-green. I also had a lot of trouble catching any fish during the period I worked there, which we assumed was due to the nasty chemicals leaching out of our skin and onto the bait when we were rigging up. (I know that any brow sweat that rolled into the eyes was awful and had to be flushed out straight away)

So I don't really think HCl is all that dangerous. H2SO4 on the other hand, I won't deal with. That stuff is nasty!