To solder stained glass and Tiffany, use soldering tin with the alloy 60/40, i.e. 60% tin and 40% lead.

How do I make beautiful solder points for stained glass?
The soldering iron must be hot enough, the solder must melt completely and the lead surface must also be warm enough. Use the correct flux, for stained glass use stearin oil and for Tiffany use flux/soldering water (lead water).
The shiny soldered points will oxidize over time. If you want to speed up this, you can patinate the stained glass panel wit black patina.
We do not recommend soldering tin 50/50 (plumbing industry) because it has too high a melting point.