My brother Rob and I have been building sterling jewelry for I would guess more than75 years between us. Rob longer than I. There is some similarity in our work but a lot of difference. One of the things we both notice is that about two or three times a year we find we have to earn how to solder all over again.
In my case I go through the inventory of ills.
Is the work clean?
Are joints tight and clean?
Is the flux fresh?
Is the solder clean?
Is the torch clean?
In my case it almost always comes back to the torch and heat. I am recent to the Smith Little Torch, propane/Oxy. When I used a Prestolite (Acetylene/Air) torch I relied on the sound of the torch as much as anything to know what the heat was. I can’t do that with the Smith Torch. Still it is heat. How it is applied, how big the tip is, and what I am using for flux. The Little Torch has a different learning curve because of the size of the flame and how it develops heat.
I am more likely to be too hot. The thickness of the metal, especially 10 ga. wire will heat up on the outside to the point the solder will flow around the perimeter of the wire but the interior will be cooler and the solder won’t flow through. It will look picture perfect until you try and shape that metal and it will break at the joint as it bends.
I have a three failure rule in the shop. If the same problem fails three times in a row. I clean the shop, have a cup of coffee, and I take a nap. Then I start over with some scrap, learn the sound of the torch as it burns through the tip I am using.
Eventually the planets realign and I am producing work again. I my case once I have eliminated the possibility dirt or contamination it is almost always heat.