The pages below are taken from an actual series of emails between me and someone who had just purchased an 1818 Broadwood square piano at auction and had no experience of piano restoration – hence the “conversational” tone. They should cover a lot of the problems you may face. Please read in conjunction with the various pdf documents on my website.
IMPORTANT, GENERAL ADVICE ON RESTORATION
One thing to say about restoring old pianos is that we try to make sure that everything we do is reversible, in case future generations have better ideas. One of the worst problems we face is trying to correct damage caused by previous generations of 'restorers'. Some old work is not usually a problem, e.g. where cloth has been replaced by red felt, or new strings are inappropriate (unless they are too heavy, and the tension has wrecked the structure.) But we don't like extra screws and bolts added to 'strengthen' the structure.
One of the commonest problems concerns glue. The originals were put together with animal-derived hot glue, Scotch glue, hide glue, all it what you will. We know it works and will last; my Blunt spinet was made in 1704, and it hasn't fallen to bits yet. If an old joint does need to be taken apart (as you will be doing for hammers, etc.) this can easily be done with water and heat. And if a joint fails, it can be re-glued perfectly with hot glue, which bonds perfectly to the traces that remain. Please avoid all modern synthetic glues, whether PVA, urea-formaldehyde, epoxy, cyanoacrylate or whatever. They generally cannot be reversed, and if they fail, the residues will prevent bonding with proper glue. We have three options:
1) Use proper hot glue. This has to be the 'right answer', but its use does need a certain amount of skill and experience, and it's not very convenient for small jobs. Also, after applying to the joint, the open-working time is quite short, and the glue can go off before the whole job is secure and clamped.
2) TiteBond Liquid Hide Glue. This is a natural hide glue as the name implies, supplied ready-to-use. It contains chemical setting agents, which give a much longer working time. The joint does take several days to reach full strength, but this is not usually a problem for us. Some say that the result is not as strong as proper hot glue done well, but it might be better to do a good joint with a slightly less strong glue than a poor job with the theoretical best. Beware that LHG has a shelf-life of about a year, indicated by a use-by date in little black letters on the shoulder of the bottle. It still works after this, but presumably not as well. It is rare to be able to buy supplies with a long remaining 'life', so we have to accept that, but beware bottles with no date on them - it might have been cleaned off! I get my supplies from Axminster, and have always been happy.
3) Seccotine. This is a ready-to-use fish glue, and is very convenient for small jobs. Some say that it is as strong as proper hot glue, and I've never had a failure. Lucy Coad sells it.
It is a good idea to remove the piano lid whilst working on the insides.
a) Dampers not hitting covered strings: It is true that the overall diameter of a covered string (core + 2x cover) is quite a bit more than a plain string. In pianos of this age, the covering is continuous, and goes from hitchpin to round the tuning-pin. The placement of the pins (nut pins in particular) should allow for this, but we all know that the various parts of the structure have moved a bit. It does happen, though, because the lower strings are quite think that they tend to curve away from the pin, rather than settling into a neat angle. Try pushing the string when it is roughly tuned to settle the bend. You may also need to crank the damper-wires, but if you do this, make sure that the part that goes through the guide runs vertically, otherwise it will jam. Make a double bend in the part above the guide to give an offset.
b) Type of piano wire to use, or not: We are in a position to be more confident about strings, partly because of the more permanent nature of metal alloys, and partly because of practical work done by Malcolm Rose and others. When I started making keyboard instruments (nearly sixty years ago!) there was little knowledge and no availability of authentic materials.
With English pianos, and Broadwoods in particular, the situation is even better because of the large number of survivors with at least partial original strings. So I can offer with some confidence the attached schedule for your 1818 piano. The scheme did not change until the introduction of the divided bridge c. 1824.
A couple of general comments: The potentially fatal error is to use strings which are too thick. This leads to increased tension, soundboard collapse, and structural failure. If anything, we err on the light side, out of respect for the age of the instrument.
Apart from the fact that it is not authentic, there are two main reasons why we don't use modern steel wire. Firstly, at square piano scalings it will be significantly under-stressed, and too rigid to vibrate properly, so the tone will not be optimum. Secondly, without a special machine it is very difficult (impossible for me) to form proper eyes. Every string on your piano has its own eye, but on a modern piano the wire is looped round the hitchpins and returns, so no eyes are necessary. There's another reason, although this doesn't affect you because your wrestpins are drilled: when undrilled pins were used (until about 1830 or later) the wire was hitched round the wrestpin so that it would not slip. This is difficult (i.e. impossible) with hard steel wire.
The problem with tuning-pins slipping happens to all pianos eventually, as the metal wears the wood. The problem is exacerbated if the piano is in an atmosphere that is too dry. The remedy with a modern piano is to re-pin with a size larger pins. Many historic pianos have been re-pinned in this way, but we don't like to do that now, as the modern pins look horrible.
So if we are going to keep the original pins, we have to make the holes smaller! The ultimate remedy is to drill out the holes oversize, bush, and re-drill. But if the problem is not too bad, there are other things we can try first.
a) Using Pin-Tite: The easiest is to use a product called Pin-Tite which you can get from Heckschers. Pin-Tite is presumably PEG or something; you dribble it round the pin and wait. It should rehydrate the wood. You can try more than one application, but obviously there is a limit.
If this doesn't work, we can try removing the pin and shimming the hole. Some folk use wood veneer (thick plane-shavings) but my favourite is fine emery paper, abrasive-side out.
b) Using emery paper: To use emery paper (or any other packing) you have to take the pin out, of course, but presumably it's loose already! I then cut a strip of paper just a bit wider than the hole is deep. (This minimises the risk that the paper is pushed down the hole and squashed at the bottom - the top edge should remain visible for at least most of the time when the pin is being re-inserted.) Then cut the correct length! it might be about an inch, but it all depends how loose the pin was. Wrap the piece around something a bit smaller than the pins, and push the cylinder into the hole. Then tap the pin in. No substitute for experience here, but if you have to tap too hard, stops and reduce the packing. If you bash the pin in regardless, it will jam, be impossible to tune the note, and very difficult to remove. Better to err on the easy side, and re-do it if too loose.
I used a fine grade of emery - something like 600 I think, but it doesn't really matter, except that the coarse grades are too thick
c) Using beech plugs: As they are quite short, you will probably need two for a wrestpin hole. To use them, enlarge the hole to the size of the plug. I'll have to confirm, but I think they are 5/16". Tap the plugs in with a little hide glue, aligning the grain. Then trim flush with a sharp chisel, and clean up with a damp cloth if necessary. When truly set, mark the middle with a centre-punch. Then drill for the pin. Experiment first on a piece of scrap. A good place to start is with a drill 0.1 mm smaller than the pin. If the pin goes into this hole with gentle tapping, the hole is too big. Try again with 0.1 mm smaller. If the pin is really tight (too tight) then use this to drill the hole. Them put the drill that was just too big into a pin-vice, and ease the hole by hand down to a depth of about 7 mm. Then the pin should tap in fairly easily, but tighten as it approaches correct depth. There is no substitute for a bit of practice. The reason for the pin-vice is that an electric drill will run away with itself.
Most of our old instruments are held at A415, about a semitone 'flat' compared to 440. Singers and fiddle players are happy with this, and if wind instruments get involved, somebody has to transpose a semitone! We will argue for ever about what pitch(es) actually were in use, but 415 is safe.
It's normal for strings to stretch for a while after fitting, generally brass and soft iron more than hard steel, which is hardly surprising. But what is odd is that within a type, some reels stretch more than others. It can take anything up to about ten tunings and a couple of months for some strings to settle down. This is why harpsichord players don't like a string to break on-stage.
Is the problem with your escapements that the spring is too strong? That could tend to jam the under-hammer on the ledge, stopping the hopper from dropping? Or is there is too much friction, or something else is stopping the key from dropping? These problems are very difficult to diagnose remotely! Something that might cure it would be to try rubbing graphite (6B pencil) on the contact surfaces. These little things make the difference between a piano that works, and one that plays beautifully. Unless springs is broken, or completely rogue, it is possible to make it weaker or stronger in effect by increasing or decreasing the coiled part. You need a pair of round-nosed pliers for this - and for many other little jobs.
When it comes to winding loops, then any method that gives the right result, and works for you is good. Apart from neatness, the vital thing is to get a good double helix, with both strands wrapped round each other. If one part (usually the main part) is straight, and the other one (usually the short end) wrapped round it, then the loop will pull out. I don't use my machine for thin strings - trebles of spinets and harpsichords. I go back to the classical method - pulling a right-angle in the wire (using a foot to hold the reel) and then bisecting the angle with a hook on a stick. Then just twiddle the stick. The hook on old tuning-hammers was intended for this.
For the case, my secret 'Magic Restorer' is a good place to start.
2 parts linseed oil
2 parts real turpentine (not white spirit)
2 parts vinegar
I part ethyl alcohol (meths will do, but it smells horrible).
Shake well in a bottle before and during use. It looks like salad-dressing, but best not to eat it. Apply with a cloth or (for really dirty surfaces) 0000 steel wool. It is best to apply repeatedly over several days. This will remove dirt, revive the shellac polish, and improve the colour of faded wood.
The cloth is 'bushing cloth', which we use in modern pianos. It is pure wool with a very tight weave, and traditionally dyed to leave a white core. I have torn it rather than cut it - this ensures that the weave is not cut, and helps to reduce fraying. If you tidy up the edges, use very sharp scissors, and be careful not to cut the long threads. It is incredibly expensive (per yard).
The proper way to clean rust of pins is to use stout leather gloves and a wire brush. It's a filthy job. I've never tried it, but if they are really bad you could try 'Kurust' or similar phosphoric-acid based rust converters. Do an experiment first, though, because on some alloys you can end up with a purple/blue tint.
As you have gathered by now, getting hold of the right leather is not easy, and tends to be a bit hit-and-miss at the best of times. There are no retailers catering for our needs, and it's not easy to deal with tanneries and wholesalers - especially overseas. And when a professional restorer finds something good, he doesn't generally want to part with it. I'm not the only one to have 'invested' in stocks that are not as useful as we hoped.
I get my veg. tanned goat from Harmatan Leathers in Higham Ferrers - near to me. I have used the 'Fine Leather' for the hammers of 18th-century pianos, and at a reduced thickness for hinges. A skin would be between £40 and £50. But Lucy Coad sells calfskin for hinges.
This leaves a problem with the deerskin. Herzog is another good supplier, but their material also tends to be soft, and they won't guarantee if for suitability for piano hammers. Other restorers have done well with elk leather, and this comes up well on Google. It seems to be more robust than deerskin. It might be worth a try, but it's a bit expensive, and unless it doesn't meet standard as described, you can't really send it back.
However, the basic rules are simple enough:
1) work from hard to soft, inside to out. Thus your hammers are probably (lime)wood cores, hard leather inner layer, deerskin outer.
2) never glue under the striking-faces - just on the sides.
3) achieve good tension so that the layers are snug - 'gapping' is fatal to tone.
When the piano was made, it's almost certain that the hammers were trimmed to fit the strings, and you may find it best to do this with new hammers. Re-fitting old ones is always a bit tricky, because things have usually moved over the years, and the alignment is critical. If fore and aft adjustment is necessary, there are three ways of doing this:
1) move the whole keyframe forwards or back
2) move the supporting 'standards' (the ears at each end of the keyframe). This will also move the under-hammers, but not the hoppers.
3) move just the hammer-rail backwards or forwards. This will not move the under-levers.
It is best to use small movements to all three of these, unless the movement is very small. You can of course move one end more than the other, but the hammers will still be in the same line. These tricks do not work if odd hammers are out-of-line.
The hinges of both hammers and under-hammers are leather, and it is not surprising that they have failed after 200 years! Replacing them is routine. They were glued into a shallow rebate, and then a tiny cover-slip glued on top. These joints can be undone by soaking just the end part in a mug of boiling water for a few seconds, when it should fall apart easily. The leather is something like calfskin or goatskin, not too floppy, and about 0.7 mm thick. But I would advise not refitting the hammers until you string the piano, working down from the top, so that you can check the alignment as you go - it is critical.