Ask Auntie EM - Sweat soldering

By now we hope you have heard about the new weekly blog post called "Ask Auntie EM". Ann Hartley of Hartleystudio and, Sue Szabo of lsueszabo , will be answering YOUR questions in a weekly post we are calling "Ask Auntie EM". EtsyMetal has over 100 members with vast amounts of knowledge and far reaching interests and capabilities. We figured if we couldn't answer your questions...someone on the team could! "What can we ask?" Great question! Ask anything! Metalsmithing, enameling, raising, stone setting, cooking, childcare, travel...you got a question, we probably have an answer! We will choose questions from comments in the previous week's post so post a question this week! Email your questions to askauntie@etsymetal.com and YOUR question might get answered next week!

This week it's me, Ann Hartley, answering a question from last week's comments. Shirlee asks:

"I'd like to suggest sweat soldering for one of your next topics ... i have a lot of practice at this yet I still find it difficult."

I wrote to Shirlee and asked her what specific problems she was having and she wrote back:

-too much solder, not enough solder
-air pockets under part of the sheet
-sometimes the little piece cracks before the solder flows
-takes so long to reach flow temp that there's a lot of fire scale
-solder refuses to reflow (flowed 1st on the back of the top piece) even if pickled in betwen soldering steps. perhaps i need to file the solder flat?

These are all common problems and I hope I can help Shirlee and some of you who are having problems sweat soldering. I know that Shirlee has a Smith mini torch so that's what I used. I will admit, it's a pretty small flame and you couldn't sweat solder anything too large or too thick with it. For this tutorial, I used a small sterling silver disc, about 1" in diameter and 24g, and another sterling disc, 1/4" in 24g as well. I needed to make a thank you gift for a friend and an initial pendant was just the right thing.

So, let's look at this first mosaic, above. In photo #1 you will see the two pieces I'm going to solder together. The smaller disc has been stamped with the initial "E" and then flattened so it's relatively flat. The larger disc is given a texture with a hammer and is also flat. Since I'm using a small torch, I used the trick I talked about in a previous post here about building a furnace to retain heat. I don't usually do this but it worked great for this project! When I'm sweat soldering I'm no hero...I use easy solder. I have done a lot of this type of soldering and I find that medium and hard are just asking for trouble. Don't be a martyr, use easy solder. I use enough to completely coat the back of what I'm soldering and I use a titanium solder pick to spread it evenly over the surface, see photo #3. There is no reason to file anything flat, if you spread it around, it's flat enough. When I'm ready to solder, I use Firescoff flux. I LOVE firescoff flux for many reasons but when I'm sweat soldering I particularly love it because it doesn't bubble or get slimy. For years, I used other fluxes and, as I heated my two pieces, they would slide all around and I had to use a tweezers to gently and repeatedly nudge them back to where I wanted them to go. Not anymore. I spray the bottom piece with a fine mist of Firescoff and then place my top piece where I want it to go, see photo #4. Now, will my top piece move a little? Maybe but not much and not at the crucial moment when the solder flows. You may need to take a fine tipped tweezer and give your top piece a nudge but probably only as you begin to heat and only once. I'm tellin ya, that firescoff is worth every penny.


So, now I start heating the bottom piece evenly. I go around and around the bottom piece, heating it evenly and never really heating the smaller piece on top. In picture #5 you will see that the small disc has settled down onto the larger disc and it's sitting right where I want it. I will stay right there until the solder flows. I will now heat this piece until the solder flows and you will see that little flash around the edge of the piece you're soldering. What I don't have a picture of is step #5 1/2 where the solder didn't totally flow out to the edge in one spot...I just hit that little spot with my torch and the solder flowed right to the edge. Then in picture #6 you can see that the solder has completely flowed around the edge of the initial disc. This picture is from before it's pickled. In picture #7 you can see the piece after it's pickled and you can see that the solder has flowed all the way around. Well, you can't see all the way around...but trust me, it is. Every once in a while, I will pickle and see that the solder didn't flow all the way to the edge. That's frustrating for sure. You can fix that by pickling and then refluxing and reheating. When the solder flows, you can *very gently* press the top piece. Don't press too hard or you'll leave a mark. Air bubbles along the edge are frustrating too. The are usually caused by dirt trapped in the flux trapped in your solder. You have three options to fix this...you can either try to soak the piece in the ultrasonic, you can use a tiny ball burr to grind the dirt out and then, in both cases, reflow the solder...or if they are really tiny you can try to burnish them out. I have found that the magical Firescoff really has taken care of both of these problems, the incomplete flow and the air bubbles.

In photo #8 I show a photo of the tweezer I use to nudge the top piece here and there until it's in the correct place. The tips are really fine and can be easily resharpened. I try to keep them as cool as possible so they don't stick to the flux when I go in for corrections.

I also checked with Sue and she had this to say about sweat soldering:

I actually almost always sweat solder with hard but that is usually cause it's an early step in the construction of a piece for me and I don't want it to slide off. I don't have any problem- I just make sure to heat the bigger piece, sometimes from below if necessary. I construct things to support the larger piece in the air so I can get heat under it if I need to- IE the piece sitting on stacks of nickels or pieces of broken firebricks. Another trick I use is to white out the top of the smaller piece- I have had solder flow onto the top of the small piece and if it's filigree or a textured piece, it's toast cause you can't file it without destroying it. To prevent that, I use a solder stop like white out to keep the top really pristine. Also, as a last resort, if you have a gap on the edge you can re-flux and put a tiny chip right in that spot and re-solder. Yes, you'll have to clean that spot up but it's better than a gap and it usually will fill it in.

So, two metalsmiths, two different techniques. I think, with practice, you can get the right amount of solder, the right amount of heat and the right touch to make sweat soldering easy.

So this week we answered Shirlee's question...next week it could be YOURS! Please email your questions for us to askauntie@etsymetal.com. Thanks for checking in....we'll see you next week!!!