Fire scale/Fire stain Questions

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Question:  What does fire scale look like?

Question

How does fire scale present on a polished piece of silver jewelry?

Answer

Please see updated information on fire scale and fire stain on my webpage:  Soldering 101 – Oxidation, Flux, and Firescale Prevention.  Updated:  1/27/17.

firescale (fire scale/stain on silver)  I think this link to my page: Soldering 101,  will help. Firescale/fire-stain usually shows up (clearly) when polished.  It looks like a purple bruise.

Question on Oxidation, Firescale, and Oxygen Concentrators

Question

“I’m producing a lot of fire scale. My studio is in my house, so I’m reluctant to set up acetylene. Is there a larger oxy/propane torch you might suggest? I’m thinking of getting an oxygen machine to eliminate buying those expensive oxygen bottles from the hardware store.”

Answer

Is it fire scale or is it oxidation, that you are experiencing?  Here’s my page on the topic.  If it is oxidation, moving to the Mapp gas and getting a larger torch tip could help.  Maybe, it is taking too long to heat your metal. When you fire metal too long it allows for considerable oxidation to develop – especially with sterling and base metals like brass, bronze, and copper.  A larger torch tip, like this #7, the Melting Tip, or the Twin Tip (you can solder from both sides at the same time),  should help heat things up faster.  Have you checked out Argentium silver?  Very awesome metal.  It contains Germanium, which is released when the metal is heated.  The Germanium coats the outside of the metal, reducing, drastically, the fire scale and oxidation.  It also takes a long time for it to tarnish – although, rates vary depending on what chemicals are present in the environment.  Please see my webpage on sheet metal and wire.

If you are getting a lot of fire scale, look into reducing your heat, completely coating your metal with flux or an anti-scale product, or don’t finish to a high shine (see my soldering 101 page for an explanation).  You can also switch to Argentium.  More information on fire scale can be found on my Soldering 101 – Oxidation, Flux, and Firescale Prevention page.  You can try a product like this: FirescoffTM.

Here’s a brief discourse on Scott’s experience with an oxygen concentrator, at Ganoksin.

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Question: My ring has fire scale, how can I remove it?

“I’m trying to solder a gold-filled ring, and I have bought the Firescoff. I have already followed the instructions step by step, but still can’t solder a perfect gold-filled ring, it still has the fire scale. Could you please tell me how to do with this?”

Answer

Firescale and Surface Oxidation both occur in metals containing copper-like your gold-filled metal as well as sterling silver, brass, and bronze – among others.

Both Firescale and Surface Oxidation look like the tarnish that forms on sterling silver although, oxidation usually has other colors in it too like browns and reds.
Surface Oxidation disappears after it is pickled (after soldering).  Did you pickle your piece after soldering?

The same is true of most fire scale.  When the fire scale does show up is usually during the final polishing stage and appears like a gray/purple bruise on the metal. (See my webpage: Soldering 101 – Oxidation, Flux and Firescale Prevention for an explanation!)

This is Oxidation from soldering on sterling silver oxidation-on-sterling-silver and on 14k gold

filled  oxidation-on-gold-filled-14k.

Unfortunately, the only way that I’ve found to remove fire scale/fire stain (easily) is to sand it off.  It’s a bit more challenging with GF as you don’t want to sand off the plating. So, take it easy. I recommend buying the thickest GF you can find which, will allow for situations like fire scale – especially when you will be soldering it. Update 1/27/17:  Please see this link on my site:  Soldering 101 – Oxidation, Flux, and Firescale Prevention for other methods to remove fire scale/fire stain.
Here’s some information from Rio Grande on Gold Filled metal.  Here’s a video from them on soldering GF. Also see, my page about Vermeil, Gold Plate, and Gold Filled.
Following is an image of fire scale/fire stain on sterling silver:
 
Another method for avoiding fire scale is to not overheat the piece.  The image above took me three tries and I almost melted the silver, trying to get the fire scale to form.
So, I guess the first objective, for you is to determine whether you’ve got simple oxidation or fire scale and then proceed with the solution(s).

Question and Answer:  How to remove fire scale/stain.

You state you: leave too many “fire marks” – what do you mean by that?  Are you using pickle to clean the metal after soldering?  Or are you seeing that gray bruising after polishing (fire scale)?  If you are seeing fire scale, try doing something like what is in this Rio Grande article. If you have oxidation from soldering, try a nickel pickle:  Here’s one article from Hoover and Strong. Here’s a product – Rio Clean Pickle – designed for nickel, brass, and bronze.

For getting into all the nooks and crannies, for further cleanup, try the 3m Radial Bristle Discs.  They work great!  To learn more about finishing please view my webpage: Finishing Jewelry and my video: How To Finish Jewelry.

Question: I have fire scale/stain on my piece – how to remove it?

6/25/16

I’m a total newbie and also don’t have any equipment yet. I am taking a jewelry class.  I  just made 2 pieces and didn’t manage to polish the fire scale off before running out of time. What would you recommend to try to polish the fire scale away? It’s mostly around/under bronze stars that are soldered onto the sterling piece. It’s tricky to get at but very noticeable. Desperate to remove it!

I’d really like to try to achieve a mirror finish. Seems like sandpaper/finishing paper might be the way to go. My other thought is to take it to a local jeweler and see if they can do anything with it.  I’m attaching pictures of the pieces so you can see what I’m talking about. Recommendations of specific papers to buy would be really helpful.

Update: 1/27/17:

Please see my webpage:  Soldering 101 – Oxidation, Flux, and Firescale Prevention for updated information on the formation of fire scale/fire stain and how to avoid and remove it.

Answer

Fire scale/fire stain is difficult to remove and the only predictable way to remove it, that I’ve found,  is with sanding or etching.  You could try using a 50% sodium bisulfate-based pickle and 50% hydrogen peroxide. One of my viewers swears that that works.  I need to experiment with it.  Check the metal every couple of minutes to see what’s happening.  You should see bubbling around any areas that contain copper. Usually, the metal will have a matt finish, after the immersion in pickle and peroxide so, you might have to burnish it with a brass brush or use a buff with rouge.  It may work – it may not.

You can fold your sandpaper into shapes – which gives you a finer point to get into hard-to-reach areas and creates rigidity to help you sand. Roll or fold it into a point or wrap it around a pencil, to get into those hard-to-reach areas (see images).  I use wet/dry sandpaper.  I buy it at my local hardware store or you can get it here, at Amazon.
sand-paper-cone Rolling sandpaper into a cone
sandpaper-and-support  Using support to wrap sandpaper around
sandpaper-folded  Folding sandpaper into a point
  I recommend working with the sandpaper wet as that: 1. keeps the dust down and 2. extends the life of the sandpaper because the particles get rinsed out and don’t build up and clog.
Another option is to apply a patina, like liver of sulfur, to hide the stain.
If you have a Dremel or a flex shaft you can use 3m bristle discs,  3M polishing pins or polishing points.
That is all that I know of for removing fire scale.  You can try preventing it by using an anti-scale coating or Pripp’s flux or by not allowing the metal to get so hot – or both!
See the question above.
Update: 1/27/17:  
Please see my webpage:  Soldering 101 – Oxidation, Flux, and Firescale Prevention for updated information on the formation of fire scale/fire stain and how to avoid and remove it.

Question: Should I protect my piece from fire scale/fire stain with an anti-fire scale coating when soldering?

Added 1/27/17

“Since you are the great and powerful guru of silversmithing, maybe you can help me.

Flux is used at the points you intend to solder to aid in its adhesion. When soldering, do I need to protect the piece from fire scale with a boric/alcohol bath first?
I just purchased Battern’s liquid flux and thought I was all set. Now I am receiving advice about the bath first. What are your thoughts? What brand flux do you use?”

Answer

Total immersion or coverage would only be important if you were concerned with fire scale/fire stain because you were creating a mirror finish, at the end.  According to the research, that I just completed, if you are working with sterling silver, bronze, brass, or gold (besides 24K) you should either:  1. flux the entire piece or 2. use a fire scale preventative.  Check to be sure that the preventative can also be used as a flux.  See my updated information on oxidation, fire scale, and fire stain.   

If oxidation is present in the metal, and it has been through several soldering/annealing steps, and you want a mirror finish, the heat from the buffing process will probably bring the copper molecules up to the surface in a random pattern.  It is explained more in the link above so, please check that out.

The reasoning behind total immersion is that the flux or preventative will reduce the amount of interaction between the 02 in the air and the metal, helping to reduce the quantity of oxidation and therefore, perhaps, reducing the chances for fire stain/fire scale to form on the entire piece.  Whereas, painting flux only at the join point only facilitates soldering and offers no protection to the rest of the metal.
Check the highest temperatures that your flux can survive at – fluxes are not all created equal.  Handy Flux is effective at 1,100°–1,600°F (593°–871°C). Caution:  Don’t purchase the wrong type of Handy Flux!  There is also a B-1 type for nickel silver and stainless steel. Battern’s Flux: 1100°F to 1700°F, (593°-927°C).  Grifflux: 1,100°–1,500°F (593°–816°C).  My-T-Flux, at Rio Grande, is effective from 1,100°-1,700°F (593°-927°C) – 200°F higher than the Grifflux.  Once you exceed the effective temperature range of the flux, it is no longer doing its job.  So, reducing heat helps to avoid stain/scale by allowing the flux to remain active.   Check your flux’s temperature ranges and try to keep your heat from exceeding them.
Cupronil, an anti-firescale and flux has effective ranges of: 1,100°–1,500°F (593°–816°C).  My thoughts:  if your flux is good until 1,700°F and the anti-fire scale is effective only until 1500°F, I’d just coat the entire thing with the flux.  Now, saying that, I have not run tests of the two, side-by-side.  That will have to wait for now!
Borax/Boric Acid and denatured alcohol anti-fire scale and flux have effective temperatures in similar ranges so, without actually testing each type against one another, I can’t recommend one over the other.  That said, I’d go with the My-T-Flux because it has the highest effective temperature range.
So, you can either run tests yourself or just use your flux and watch that you don’t overheat your metal.  A smaller, hotter flame can help – focused soldering – so that the entire piece doesn’t get overheated.
Another option to avoid fire scale/ fire stain is to not have a shiny finish.  Think finishes:  textures, patterns, surface treatments, patinas, etc.

Question: Does Pripps Flux work better than boric acid and denatured alcohol for preventing fire scale/fire stain?

“I use the boric acid denatured alcohol mix for fire scale prevention on sterling. I wire brush the sliver with some dawn soap first, dry the piece, stir the boric acid mix and dip the silver. Next, I heat the silver to a dull red and quench it. The only time that I seem to get fire scale is if I overheat the silver. I can repeat the brushing and coating if I happen to see some fire scale. My question is whether you think the Pripps flux works better for fire scale? Some jewelers swear by it but I have not tried it. The Pripps flux might be easier for the students to use? “
Answer

Do you create a high polish on your finished pieces?  That is when the fire scale/stain shows up.  It doesn’t always happen though.

I don’t think any one type of preventative works any better than another – although, people can get pretty heated up in the defense of their fire scale/stain preventative.  I use just plain flux and try to avoid overheating.  Anything that reduces the amount of oxide development, works.  The temperature range of the flux/dip is crucial – if pieces are heated past the max temp range, the flux/dip stops working.  Most have working ranges of up to 1800°F.  I think, that if you aren’t seeing fire scale/stain, then you are doing something right and I’d keep doing whatever you are doing.  Although you do have most of the ingredients so, you could make some up and see what you think.  Wish I could be less vague but, I haven’t found anything that I feel is superior to another – yet!

*There are other fluxes/dips that have higher ranges but, they are usually used for platinum. Also, soldering on charcoal helps because it creates a reducing atmosphere.

I don’t think the Pripps would be easier for students. Although, I haven’t tested that theory.

What is the best way to avoid fire scale/stain altogether?

Use Argentium silver. Period.

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