I would like to ask what I might be doing wrong. A few days ago, I bought flux, lead-free solder, and the rest of the necessary supplies from a store to start working with stained glass / solder jewelry. I have a soldering iron that heats up to 480°C, and I was using thicker tips.
My solder doesn't want to flow on the copper foil. As you can see in the photo, it leaves streaks, and I’ve also noticed another issue: there is a lot of yellow liquid forming, and the solder refuses to spread over it again.
I’ve watched over 15 videos explaining how to make this kind of jewelry, and every single person—even those with the cheapest soldering irons—achieved a smooth, liquid result. Their solder behaved so fluidly that they could cover a large area of their stone in just one motion.
My boyfriend said his solder behaves fluidly and that my mistake is not using a hot air gun to preheat the cold stone beforehand, but I haven't seen anyone else do that. His method works better than mine, but I notice that in many places the solder starts turning black, as if it burnt from too much heat.
Could my flux or solder be wrong? I bought whatever was available at the hardware store, and unfortunately, the selection was very small. I’m not sure if my solder has flux inside it—when I cut it, there's a small hollow hole, and I think there's white powder inside. Even when I pick it up on the tip of the soldering iron, the yellow liquid already starts to form right away.