I have an old Hardman upright piano that's approaching 135 years of age. It's in decent shape considering, but is about 3 semitones flat.
Is it even possible to get this old girl back to concert pitch? If so, how? What's that like?
When i was a kid i worked with my blind gramps who tuned for a living, and i recall him going across some pianos several times, but i was more of an observer than a student. Wish i'd paid more attention now!
It's got a very good maker's name on it, but the answer depends what condition it's in.
If it's been allowed to drift 3 semitones flat over a long period time, most likely nobody has bothered much about looking after it. If it isn't reasonably well in tune with itself, personally I wouldn't even bother to try, because it certainly won't hold its pitch any better afterwards.
If there is corrosion on any metal parts, that will increase the risk of breaking something. Of course broken strings are replaceable, but if you want to turn it back into the "top-quality" instrument it once was, you might need to consider completely re-stringing it, or risk having the replacement strings sound different from the rest.
If it's 3 semitones flat, the string tension is only about 70% of what it is supposed to be. You certainly don't want to raise it by that much all at once - you might even crack the iron frame. "Rough-tuning" the whole instrument up a semitone at a time might be OK - though half a semitone at a time would be safer!
If you discover any seriously loose tuning pins on your first pass, either give up, or (if you insist on doing things the hard way) figure out how to fix that problem before you go any further raising the pitch.
Unlike violins, pianos don't "improve with age" - the soundboard inevitably changes shape gradually under the string tension and loses its original resonance.
Despite all these negative comments, one of my favorite pianos (owned by a friend) is a huge English "no-name" upright dating from the middle of the 19th century, with a wooden frame and not overstrung - but if I used it as my regular instrument it would be reduced to firewood within a few months.
Just adding a little to alephzero's great answer - some Hardman pianos had wooden frames. If yours has dropped that low, it may well be because of its wooden harp. If that's the case, it probably won't pull back to concert without dying. If it is indeed an iron frame, then over a 6 month period, working carefully, it may be possible. Speak to Hardmans about its original pitch - that may have been lower than A=440Hz.
Also be aware that if it has to be moved to be worked on, it probably won't appreciate that, and you can add another month into the equation, for settling. I'd take it to a semitone below concert, and leave it for a couple more months. You say you've done several already - you should have enough experience to work on it o.k., but if strings break - they're very old - it will be time to leave well alone.
Sure, have a go! You have some piano tuning experience. Bring it up in stages. You'll soon find out if some notes won't 'hold'. You may well break a few strings. But what the heck. You're starting out with an un-playable old piano, of little value. At worst that's exactly what you'll end up with.
