I've just bought a bundle of new memory with a stick of used Samsung PC2100
(256mb) thrown in there too.

It looked in good nick until I noticed that 2 of the gold pins on one side
had either been blacked out deliberately or had burnt out. I suspect the
latter, as the tiny little gold circles (whatever they are) are also
'burnt'.

I know NOTHING about electrics, but I did vaguely recall reading of
conductive paint or some such. Is this an option or is my chip a lost
cause? I heard that memory often comes with a lifetime warranty, but can
find no memory specific stuff on Samsung's site, and I have no proof of
purchase anyway.

Even if it SEEMED to be working, I'd still give it a good bashing with
Memtest to make sure it REALLY worked.