Hello! So I’m soldering copper, to copper, using copperphos (so flux in it) no problems. Loving it actually. My question is, is there a “proper” flux for copper? I’m kind of confused on what(i.e different fluxes) is for helping to keep the “firescale” off of the entire piece and what it needed to help with just to soldering join. (I know I don’t need any flux on the solder point because it’s in the paste solder I use.) I’m actually kinda confused on what is considered “firescale” as well…is this just the oxide that builds up during the soldering? Which is easily removed via picked pot? I’ve read many things regarding this all with a little different interpretation and all of them regarding silver NOT copper…don’t know if this makes a difference
… ANYWAYS… I have used FireScoff and my own mix of 50/50 borax((instead of boric acid due to the high heat needed for copper))and denatured alcohol (which was HORRIBLE it left REALLY bad bubble like stains that would have taken forever to get off via sanding and took a while in the pickle pot and advice with this as well would be awesome!). I dont mind using the pickle pot but the super pink (I’m assuming it’s extra copper build up that does this) is just a little annoying to have to get off. So that’s why I’ve been looking for ways around this. Sometimes once I quench it I can simply rub the oxide build up off with my fingers or a paper towel which always surprises me (I think it might be due to the residual FireScoff that’s been sprayed onto my magnesium block from previous projects that may be doing this magic?) Any info would be wonderful. Thanks!
I like Pripps flux I make at home from Tim McCreights book The Complete Metalsmith Pro version. I also like Battern’s flux or Handyflux which I use because I bought them, Pripps is my favourite however. Medium silver solder usually works best with copper although I tend to use the hard solder just because its close to hand.
Firescale is not really an issue with copper. What you are most likely seeing is carbon buildup which often happens if you are not getting hot enough, fast enough. Copper melts at much higher temperatures than silver, somewhere around 2200 so there are no worries about a meltdown with copper.
Firescale is more frequently an issue with STERLING silver or other silver alloy containing copper. When you overheat the sterling the copper in the alloy comes to the surface of the metal and presents as rather dark purplish stain that is almost impossible to remove because its part of the metal. Again, this is caused by overheating the sterling.
Here is a good example from Firescale
Nancy LT Hamilton has some very good tutorials on her web site and video’s on Youtube.
Aurora
There are many fluxes on the market that work great on small copper pieces, but fail miserably on larger ones, so the best one depends on what you are asking it to do. I work entirely in copper, but I ran into serious problems as my backplates became larger. First, I needed more heat and solved that problem with a new torch, but I struggled to find a flux and solder combination that didn’t fail before the piece reached soldering temp. I’ve never used paste solder, but Handy Flux, Firescoff and My-T-Flux all burned off before the backplate reached soldering temp. I kept trying one combination after another but nothing worked. Finally, I switched to white Stay Silv and hard silver solder and had instant success. Copper doesn’t develop firestain, but the extended heating time can cause dark stains that pickle doesn’t remove. Now, I flux everything. It adds extra protection for the solder and bezel and leaves fewer of the dark stains to polish out. I flux the back and let it dry, then flip the piece over onto a hard charcoal block and start fluxing and assembling the piece right on the block. I let it dry for an hour then heat it gently until the bubbling stops; it becomes sticky and helps hold the solder and bezels in place during soldering. Stay Silv does take extra time in the pickle and I still end up with some staining, but scrubbing with a soft toothbrush and a little baking soda followed by another scrub with dish soap usually takes the rest of it off. I apologize for the monologue, but hope it helps clarify a few of your questions.
Alaska Silver
Perhaps there are geographical differences at play here? I was taught by a accredited instructor that firescale is the dreaded purple mark while fire stain is the colours you get by playing the torch flame over your metal. Some people even use both words interchangeably for the purple stain in overheated sterling.
Dark oxide buildup was simply known as carbon or oxides.
Aurora
I can’t site my source, and now I’m afraid I’m spreading misinformation. If I find the article I was thinking of I’ll share it. 
I found my source. The following statement by Nancy LT Hamilton, was taken from her blog.
“”Jewelry Materials: A Guide to Working with Common Alloys”, Technical Editor: James Binnion, states that:
“Firescale and firestain are often used interchangeably, but technically can mean two different thing (sic)….Firescale is a dark gray to black scale on the surface of the silver…Firestain is a dark purple subsurface stain…””
Ms. Hamilton also points out in her blog that even the masters hold opposing positions about the definitions for both terms (firescale vs firestain). I don’t think it’s a geographic difference, and believe it’s due more to murky definitions within the industry itself.
Source: Soldering 101 – Oxidation, Flux and Fire Scale Prevention | Nancy L T Hamilton
Thank you so much! Now I feel much more confident in my understanding of firescale and stain. He site is amazing, I can’t believe I didn’t think to look there seeing as I’ve gone to it a bajillon times before haha
@AlaskaSilver
No thank you so much for your “monologue” I found it to be more of a holy grail of information! I’ve found using the charcoal block super helpful (idk why I didn’t try it sooner seeing as I have had one for some time now) I’m going to try your suggestion but use the paste solder and I’ll let you know the results! I must be lazy or something because I cannot stand the silver solder on the beautiful copper (I really do not like silver mainly due to the color which is why I use copper) I really deeply appreciate the insight. Thank you so much!