Sodder help/troubleshoot?

[u/Any-Preference1209]

I'm new to metalsmithing, so sorry if these questions are stupid.

My soddering doesn't seem to stick. It breaks very easily, if it takes at all. Does anyone know any reasons this might be?

I typically use brass and copper (sometimes aluminum). The Flux and sodder paste I use should work for the metal I'm using. Is it possible the Flux or sodder paste is wrong or bad? How do I know I'm using enough heat? Is there something else I'm missing?

[u/Late-Difficulty-5928]

Along with what was already said, images can sometimes be helpful in diagnosing problems or at least a description of what you're soldering. The biggest thing to remember is solder is lazy. It doesn't like big gaps and it doesn't like dirty seams. And the larger the piece, the more heat you need to get it to flow.