In short, Go Green.
The picture shows the result of my experiment in casting a solder ingot: inside the mould its says "instructables" but sadly, solder does not take details very well.
The movie shows the process: the loose solder in a stainless steel dish is heated and stirred with a hot (50W) soldering iron, and then poured into the mould.
I have gotten into the habit of saving all the solder that comes my way, and I keep a receptacle (with lid) on my table for this purpose. When it gets to a respectable amount it is cast into some shape and stored. Some day I might attempt making a really big sculpture with reclaimed solder.
Lead is not poisonous. The compounds of lead are, however. If you keep all the lead containing alloy that comes your way as the metal, in some pleasant shape, cast or sculpted into some form that is pleasant to the eye, you will be helping the environment by keeping at least some of its potential pollutants at bay.
Start saving your solder today. Read on to find out how.
Step 1: Scrounging for solder
All this was after I had tried wiring up a few circuits without soldering. Twisted connections were no good. They tended to loosen up when components were added or changed.
So I started scrounging solder from wherever I could. From the bases of old light bulbs - this was hard to melt, due to it being mostly lead, but it could be used after mixing with the regular kind. I looked up why from books in the library, and so got interested in melting points of alloys and things like that.
If somebody gave me a radio to repair I would be sure to get some solder from inside that, too. I learnt how to make joints with the minimum amount of solder.
And kept on saving all the solder I could find.
That involved cleaning my desktop very carefully after a soldering/desoldering session, and brushing all the bits of solder into a tin. I made it a tin with a tight lid after accidentally upsetting it one day and scattering precious solder on the floor.
The key to succesfully reusing solder is the flux. I bought some rosin to use as flux, after the general wisdom of the practising electronicians of that age - those gurus who were capable of repairing radio sets, and made a good living doing so. They all were using blocks of rosin at the bench. It was solid, smelled nice when heated, and the residue was not corrosive. There was a knack to getting it to the solder joint - it had to be carried on a heated screwdriver tip or copper wire.
The surest place to find rosin is the music shop. Rosin is the stuff violinists rub their horsehair bows with so that it makes squeaky sounds when they rub it against stretched wires on that wooden contraption. Sure, there might be cheaper places, but if you want some, and do not know where to go to, try the music shop.
The rosin does to solder what soap does to water - it makes the solder flow easier, by reducing the surface tension. It also reacts chemically with the oxides of the tin and lead, and turns them back into metal again.
The picture shows a collection of loose solder, as discharged from inside my desoldering pump.