Hello, Can anyone please help me know better why pits sometime occur in my solder seams? I imagine it might be due to overheating but I would love to have a clear understanding of if this is so and why! In particular, I am referring to some seams on bezels in silver, that were not particularly large pieces. The torches I have are the Swiss torch, with Oxygen and Propane.
1 Like
You are likely getting the solder hot enough to vaporize some of the zinc. Are you using hard solder to solder your initial bezel seam? Hard solder has the least amount of zinc among the typical three solders that we use and melts at the highest temperature of the three. You need your torch to be hot enough to get in and get out. The longer that you heat the solder in the joint, the more likely it is that you will drive off zinc. Make sure that the joint fits perfectly and that it is clean. You might also coat the entire bezel with a solution of boric acid and alcohol, burn off the alcohol and then coat the seam with a high temperature flux. You aren’t alone. I suffer from this problem once in a while and I have to go back and apply the basics making sure that I don’t skip one or two in my haste to get it done. This can also happen after the fact as you solder additional seams in the piece. Additional seams should be soldered with lower temperature solders to avoid heating one seam when you work on another enough to cause the solder to flow again in the original seam. If you can, don’t do any finishing on the first bezel seam until you are done with all of your soldering. This might allow you to finish into the seam to a point where the solder doesn’t have pits. If you do find pits, you might try to flatten them out with a rotary burnisher. You can buy them or make one from an old bur. You torch is fine. Actually, it is very nice. Others may have different ideas, but these are mine. Good luck…Rob
3 Likes
Thank you! Yes, I am using hard solder for the most part. Thank you for this explanation and your suggestions, it’s very helpful and greatly appreciated!
Best wishes,
Barbara
2 Likes
Probably not zinc vaporization in your solder. Zinc vaporizes at 1665 F, that is 25 F higher than the melting point of sterling silver at 1640 F.
Dirt, and other contaminants can be vaporizing at soldering temperatures but more likely is oxygen that is being absorbed by the molten solder coming out of the solder as it begins to solidify. Silver has a crazy ability to absorb oxygen while it is molten but can’t hold it as it returns to the solid state and it comes out of solution as bubbles. Apply enough flux to protect the joint and keep the joint area covered and keep you soldering times as quick as possible to prevent absorbing too much oxygen.
6 Likes
All super good advice from Rob, but I would like to emphasize one point he said: “You need your torch to be hot enough to get in and get out.”
Once the solder flows, take the heat off.
All the best.
~AJ
3 Likes
Jim…You know a lot more about what is happening chemically and metallurgically than I do. I just know how to avoid pits (most of the time), not why. So thanks for the clarification. I also really like looking at your work. Thanks…Rob
1 Like
Thank you Rob,
There are multiple reasons for bubbles. At higher temperatures zinc vaporization can be a big issue for solder seams at temperatures above sterlings melting point.
One thing that I am curious about. When I cast an ingot of sterling silver, usually in the 2 ounce range and 1” X 2”X maybe 4mm thick, as I roll it out to around 16 gauge, I will get what appear to be small blisters after annealing and pickle. They roll out, but reappear after the next pickle. I am curious what might cause these blister. Thanks…Rob
Hi rob,
oh, the answer is in the brepohl book…lemme look…
juiie
i think there are posts on this too…
What Jim Binnion said. I’ve done a LOT of silver work in my career. The magic key is cleanliness and a good flux. I have found that liquid flux burns off quickly just and doesn’t work as well as a good paste flux. When silver soldering I first dip the piece is denatured alcohol and powdered boric acid and then flame off the alcohol. I dim the lights so that I can see how hot things are and start off with a slightly bushy flame and wave it quickly back and forth over the piece I am working with. When it starts to get a warm glow I then tighten my flame and focus on the seam. Silver is kinda like a transactional romantic relationship. It like things hot clean and shiny.
2 Likes
Blisters like you refer to are trapped gas. There are several ways you can end up with them in your ingot. First guess is trapped oxygen that comes out of solution as the metal solidifies. Silver can contain as much as 20 times its volume in oxygen when molten. However it cannot hold it in solution as it returns to solid state. If that gas is trapped by metal solidifying around it remains as bubbles in the metal matrix. Turbulence in the pouring of the ingot can also trap gas in the ingot. Other means of trapping gas in the matrix are not typically going to be found in studio produced ingots.
As you roll the metal down the thickness of the metal around the bubble is reduced. When heating the gas bubble tries to expand, if the metal surrounding it gets thin enough it will form a visible bubble distortion on the surface of the metal. When you roll it out it flattens the bubble back down into the surface. When you heat it to anneal the gas again expands and the bubble reforms.
2 Likes
I guess that the best way to avoid it is to cast under an insert gas. Something that I don’t have the ability to do other than to switch to my electric furnace and keep the cover on it. Are you describing actual bubbles of just an area that has gas mixed with the metal?
2 Likes