Solder Tip
Common solders are a mix of tin and lead. The numbers that describe each type of solder refer to their % of each metal in that solder. The melting temperatures are: 50/50 421 degress F.
60/40 374 degrees f. They "set up" at 361 degrees F. Most lead free solders are usually within a 430 to 465 degrees F. Melting temperatures of lead and zinc came also vary. Lead came usually melts at 620 degress F and zinc came at about 780 degress F.
Many people use 50/50 for the back side of a lamp or to fill gaps in a project. If you have big gaps in a piece that needs to be filled, turn your irons up and use the 50/50 solder. Once it is set up, turn the iron down and use 60/40 to tin and bead. Since 60/40 becomes liquid at a lower temperaturethe 50/50 patch doesn't melt when they solder over it with the iron turned down.