I’m a beginner, and recently switched to using a borax cone as flux. I keep the dish clean, use distilled water with it, and always use a clean brush to apply it, but I’m having a lot of trouble with solder flow. When I apply heat, the flux looks dirty as it bubbles up and I have so much trouble getting the solder to flow that it ends up causing firescale and heat damage to my silver. I make sure the silver and the solder are clean as well, I would appreciate any ideas you all may have!
I believe that the borax you are describing is simply a barrier flux and you should also be using a solder flow flux as well. I like to dip my solder pallion in the solder flow flux, place it, heat the piece with a lamp to dry the flux, and then add the borax flux. I hope this helps.
I use Handi Flux on silver soldered joints. It provides a good and fairly long lasting O2 barrier. Borax works on gold. You do have to make sure that your joints are tight, the solder, metal and soldering pad are clean and you use enough heat. The quicker you can heat up to the solder flow point without damaging another area and get out the better. I will also coat the entire piece with a Boric acid/alcohol mix to prevent fire scale. You will sometimes get a glassy deposit around the joint after you solder and pickle. Don’t try to file or grind it away. Put the piece in water and let it soak for a while, the glassy deposit should dissolve in the water. This is a good time to take a break. Good luck…Rob
I would agree that the borax cone is reputed to work best as a barrier flux and another is needed at the joint. However, speaking just from what I read from multiple authors, the best alternative would be Prip’s flux or cupronil. You can make Prip’s or you can look for my post on making your own cupronil. It is basically using Disodium Phosphate in place of the TSP in Prip’s. I figured this out by looking at the MSDS for cupronil, which is freely available. Either of these would be sprayed on (could probably also be brushed, but less efficient this way) and would be both a barrier flux to firescale and a soldering flux. The experts say it works better than the traditional borax cone. The chemicals are all available on Ebay. Just my two cents. -royjohn
Boric acid and denatured alcohol is what’s used as a barrier flux. I’ve used Handy Flux for 47+ years and it’s always worked well for me. I see no need to switch to a borax cone. I do add a little powdered borax to my barrier flux.
I’m a beginner too, and my beginner’s mind thinks that your problem is that your metal is not clean despite what you think, or you are shy about adding heat fast and hot. Flux turns color during heating and that might be what looks “dirty” to you. Google “Andrew Berry solder” and look at this guy’s borax cone! His soldering playlist is Soldering - YouTube
I have used a number of barriers over the last thirty years. The easiest for me is Boric Acid/Alcohol. While this is a great barrier it is subject to a few variables. Mostly the saturation of Boric Acid in suspension in the Alcohol needs to leave an even white coat over the metal. Too little and the coat is thin and inconsistent, too much and you may get a lot of bubbly melt going on. I know everyone says this is strictly a barrier flux but I have quite successfully soldered directly through it without Handi-flux or Battern’s, or My-T-Flux. Usually because I was tired or not paying attention.
I think I got this method from Tim McCreight’s book or some other manual.
When I am using a lot of clear surface on a piece I will make a dip of Borax and boiling water. As much Borax as a cup of water will absorb. I will gently heat the piece to a straw like color and dip it into the mixture and let it dry. Then I will solder through the barrier with a liquid flux like Battern’s or My-T. I know that’s a lot of steps but then I am retired.
on another note…i sometimes have issues soldering sterling silver, when using hard plumb solder…sometimes it just doesnt want to flow…
i have read older forum posts about this, including. comments about various solder brands and melting temps…
in my personal case, i find i have success when i use higher heat, and get in and get out…
i find when my temp is slightly lower, and i am tentative…i have issues…
you said that the flux was brown and bubbly…perhaps you are not hot enough, in the right place, at the right time…(i know…vague!)
i would suggest that the flux shiukd be getting glassy when temp is hot enough
i will say tgatthat flow temp on hard can he bery close to meltiing point…
Hmmm, I have used nothing but a borax cone with distilled water and a ceramic dish. I have not used anything else for a flux and have no trouble ever with solder flowing and very little to no issues with fire scale. I was under the impression that its pretty standard, but apparently that’s not the case? I might give something else a try just for kicks.
Good point regarding the possibility of temp being too low and also possibility of solder brand being an issue.
I used borax and distilled water as my flux for a few years and switched to using a borax cone and distilled water over a year ago. I like that I can control the thickness of my mix and only make what I need as I need it. I once read that the only reason solder won’t flow is because the flame isn’t hot enough and that’s what I’ve found to be true for myself. I have three different size torches with adjustable flames and if it’s not flowing with the one I’m using, I use the next step up. Took some practice when I first started to learn to pull back, circle around or keep the flame stable to avoid the issues you mentioned. I work with Sterling Silver. Hope that helps or gives additional insight.