Likewise with rolls of solder. While the lead and tin alloy works well, it can also work like "black magic" when the % of each is altered. A mix of 60/40% tin/lead, with have different melting temperature and flow rate that a mix of 40/60% tin/lead. While both work, it is good to know when to use each. But, again, a topic for another thread...
Don't forget ROHS and no-lead solder, and silver solder too.