The local technician had recommended a new set of bass strings. I went thus prepared to take a rubbing…
However, I did some tests on the very worst (either dead or buzzing) of them. None of those I tested had any added twists – one even had negative twist (ie in the wrong direction!). They revived well.
So, I added 3-4 twists to all the strings that were acoustically dull/buzzing. Again, none had added twists, whilst some had negative twist. (It is usual for string makers to add 1-2 twists to each bass string on fitting them).
I went on to revive the complete set, thus saving the pianist several hundred pounds!
NB: It is not possible to revive Hexacore strings (eg those used by Grotrian-Steinweg).
Here’s a pic of the set half way through the revival (most of those that look brighter have been twisted, thus showing a new side):
(Putting on individual new bass strings without changing all the other strings never sounds good – revived strings blend in, whereas new ones make for an unbalanced sound, which can’t really be compensated for via voicing)