Firestain appearing at the polishing stage?

[Lux Aeterna]

My first question here - please be gentle with me (I've already tried the Search function).

I've been a good boy (I think)...

I bought a decent sized (Orca) torch, so I could heat the Silver more quickly than I could with a hand torch.
I've reduced the amount of air in the flame, so that flecks of yellow are visible and the flame is more 'roary' than 'hissy'.
I solder on a charcoal block. Every time.
I try my best not to overheat the Silver. I hold the flame on the join for 1 second after the solder has melted and then take it away.

...and I still get some firestain (although not as dark / deep as I used to) - even on simple pendants, with just a single jump ring soldered on for the bail.

Then I read that firestain can be 'brought out' by the frictional heat generated in the polishing stage and I think this may be what's happening (we use Tripoli and Rouge in our classes). It started appearing again yesterday, on a small batch of simple pendants, at the polishing stage, so I held a couple back and polished them at home with finer micromesh grades and fine 3M radial wheels. Guess what? No firestain.

For my next steps, I'm considering...

Abandoning the coarse wheel / Tripoli in favour of micromesh, then finishing with rouge on the soft wheel.
Checking out boric acid, or some other proprietary solution, as a preventative (suggestions / recommendations sought).

Does that sound like a plan? Any suggestions / constructive criticism welcome.

[Dennis]

Hi lux, some people are obsessed with a mirror finish, but the less glossy, the less the firescale will show.
You are aware of what brings it on, but for some small jobs you might be using too big a torch, when a small hand torch will do.

Equally, it is not necessary to use hard solder towards the end of a soldering sequence (or for that matter at all), when easy solder will do.

The simplest anti-oxidising solution is boric acid dissolved in meths (or vodka), brushed on to warm piece, but not left open near a flame.

Lastly you might settle for a set of radial disks for your smaller pieces, which used in order, will give a shine without compounds , or heat. For non flat pieces, consider a tumbler. In some cases, particularly chains, a soapy brass brush is good. Dennis.

[Lux Aeterna]

Thanks, Dennis :)

Just to expand a little...

I do tend to do multiple soldering operations (adding shot and wire decoration), but 'work down' the solders starting with hard on the bezel join and jump ring on the base (e.g. of a pendant), then medium to attach the bezel, easy for the deco, then extra easy for any extra deco and closing the bail.

I still do use a (Proxxon) hand torch for some smaller pieces and reckon the maximum size it can handle in good time, is around a square inch or so of 1mm sheet with bezel and some deco. It's true the Orca can be a bit fierce sometimes, for what I do, so I keep it turned fairly well down and have only used the smallest nozzle so far; I also keep the gas regulator on the propane tank at around 50%.

There is a tumbler on the shopping list - I think I'll kick it up a few places, as a lot of my pieces are lightly domed. I do have a set of small radial discs in six grades, but have found that sometimes (especially on the coarser ones) a piece of grit becomes overly exposed and starts adding scratches, so I've become a bit cautious about using them. I will check out the soapy brass brush sometime and seek instruction on how to use boric acid.

[knucklehead]

Hey Lux

when you put a piece in the pickle after annealing/soldering, the pickle will remove that top layer of copper resulting in a silver surface, but that surface in only microns thick and when polishing that can be worn away to reveal more copper underneath. I understand there are 2 methods to resolve this 1 being elbow grease polishing to reveal of the silver underneath (and if those radial wheels/micromesh are working for you, use them) or 2 dip solution in nitric acid solution (40% to water) which will remove copper oxide. this method is referred to as bright dipping ...although I would not recommend anyone to keep nitric acid ...only heard about it
so i would say stick with your new polish materials

[Dennis]

Thanks, Dennis :) seek instruction on how to use boric acid.

Find a container with a screw top, that will admit a flat bristle artists brush. Half fill it with meths and tip in as much boracic (boric) acid crystals as will dissolve and then some. You only need to buy a small box from a pharmacy.

Warm the piece, as you do for fluxing and brush on evenly. It dries quickly to disclose un-fluxed areas. Then do the other side if required. It is best rested on wire mesh.

As you see, this can be fiddly and time consuming. So I only do it to sheet prior to annealing and it helps to keep it pristine for the next stage (usually roll texturing). Dennis.

[CJ57]

Hey Lux

when you put a piece in the pickle after annealing/soldering, the pickle will remove that top layer of copper resulting in a silver surface, but that surface in only microns thick and when polishing that can be worn away to reveal more copper underneath. I understand there are 2 methods to resolve this 1 being elbow grease polishing to reveal of the silver underneath (and if those radial wheels/micromesh are working for you, use them) or 2 dip solution in nitric acid solution (40% to water) which will remove copper oxide. this method is referred to as bright dipping ...although I would not recommend anyone to keep nitric acid ...only heard about it
so i would say stick with your new polish materials

Unfortunately pickle won’t remove firestain and you either have to work through the grades or wet and dry or micromesh and polish it out. I use a bristle brush with tripoli or blue luxi to begin with and then a rouge or white luxi mop . Sometimes if I’m lazy I’ll do a matt finish to hide it but as it starts to tarnish there is a shadow and I know it’s there so even if I intend a matt finish I make sure any firestain is polished out first before I revert it back.

[Dennis]

No one has mentioned this yet, but because firescale is quite deep seated and requires aggressive treatment, a green Scotchbrite wheel (used dry)on the lathe, or a small one on the hand piece is a quick way to get it out.

The curse is that when you re-polish you can often see some that you have left behind. Looking at the piece through greaseproof paper, can show it up before re-polishing. Dennis

[CJ57]

Beware being heavy handed with a scotchbrite mop as I’ve had a drag appear in the past but I do use a bench polisher. I usually find my missed firestain when it goes in the lightbox to photograph and there it is and it’s back to the bench!

[enigma]

I find that coating the whole piece with Auroflux before soldering or annealing helps prevent firestain forming.
If I do get some I polish out with the Everflex burrs which are my polishing regime anyway ( I can't use compounds as most of my pieces have horsehair in)
Its annoying when you don't see it until the final polishing grade but it is there before, you just have to get better at spotting it before you reach the mirror finish and polish it out with the rougher grades.
Obviously also try not to overheat as far as possible.

[Lux Aeterna]

Thanks for the replies and advice, everyone :D

I'd prefer prevention to cure, so will be checking out coatings (nitric acid is a bit too scary) - but how do I stop the solder flowing everywhere, if the whole piece is covered in flux? Also: is there any particular reason for brushing on the flux - can I not just dip?

I love the greaseproof paper tip BTW - hadn't heard that one before.

Luckily this is only surface firestain and not scale. I have had the latter once before, early on, probably due to heating too large a piece with too small a flame.

[Dennis]

If the torch is directed correctly, solder will sink into the join and will only spread if there is too much of it.

Brush on flux for economy and for it to cling evenly the piece should be gently heated.
If you wish to dip it, that's fine for an aqueous solution, but dangerous with an open container of a flammable mixture. Dennis.

[china]

When I use Stirling Silver (Rare these days I mainly use Argentium) I coat with boric acid and I don't seem to have any issues with fire stain

[Dennis]

To be fair Bob, Argentium is firescale resistant. Dennis.

[TDA20]

I think that's what Bob means Dennis. That he only uses boric acid when working with standard sterling instead of Argentium.

[enigma]

I wouldn't dip it as you would be risking contaminants entering the flux which could create issues with soldering later on.

[Lux Aeterna]

OK, thanks again to all. The only way to find out how it works for me now, is to go and do it. I'll experiment with some scrap first...