In message , Richard G3CWI
writes
Jack Jones wrote:

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

Sad to say it has definitely gone off. Safe disposal will be costly so
please pack it carefully and send it to me QTHR where I will dispose of
it at no cost to you (probably on ebay).

I have solder well over 20 years old that is still fine to use...

I was also going to suggest that, but I realised that it would be being
a bit cheeky!
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