Hello Don Yes - I use the knotted string technique quite frequently - but only on the bass (covered) strings. The only time it is (sometimes) impossible is when there's an agraffe nut. But I have been known (in a case of real difficulty) to strip back the covering and reef-knot on an extension (mic. up the core first) this got me out of that problem - and, oddly enough, the quality of the sound was not that inferior to the remaining strings.... This is why, when I restring the bass end of a piano, I always keep a selection of the cut-off ends as they're often thicker than the reels of string readily available. Bit of kit really. Regards Michael G (UK)
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