Jack Jones wrote:

In a burst of enthusiasm when I was much younger, I bought a large reel
of solder which I barely used.

It must have been at least 20 or more years ago. It looks similar to
this:
http://img-europe.electrocomponents....C557130-01.jpg

Now I need to do some soldering again. Would that old 60/40 multicore
of mine have deteriorated?

I have an ancient reel of solder. I can't say I've noticed it 'go off'. It
may vary with the flux formulation.

Graham