Broken Strings
Let's suppose you have stepped into a time machine which has transported you back to the year 1875. You are walking down the main street of a frontier town in the American Old West, when you hear a loud bang coming from the saloon bar, after which the tinkling of the piano falls silent. Should you:
(a) Pelt down to the local sheriff's office as fast as your legs will carry you to warn everyone that the Coyote Kid and his band of outlaws are back in town or;
(b) Send for a piano tuner?
The answer is - b (well, possibly).
I recently read an article on the internet, on the subject of myths about the "Wild West". It mentioned that guns were not nearly as ubiquitous as you might suppose if you learnt about the period from John Wayne films; many towns and cities had rules prohibiting the carriage of firearms. So if you heard a sound like a gunshot coming from the saloon it might not be a six-shooter going off but... the sound of a string breaking on the piano.
In the mid-19th Century it was not uncommon for piano strings to break when the instrument was being played, although more usually when subject to a virtuoso attack. Franz Liszt (1811-1887) was famous not only for breaking strings in prodigious quantities in concerts (apperently people would fight over them as souvenirs), but sometimes even for cracking the case of the instrument! Fortunately modern pianos are much more robust than in Liszt's time, with cast iron frames and piano wire much improved from that used in the past; however even today, it is not unheard of for a string to break while being played (though it is fairly rare).
Piano strings, under high tension, can also occasionally break in the course of a tuning and they do go off with rather a spectacular bang. For this reason, if you're very nervous (should I say highly-strung?) don't try and tune a piano. However, as I've had a few jobs recently that have involved replacing strings, I thought I would explain a bit about why they break and how they can be replaced.
Why do strings break?
Piano strings are made of high-grade steel wire, which is normally just polished (sometimes plated). The thicker bass strings have copper windings around a steel core.
The most common cause in my experience is pianos that have not been tuned for a long while and/ or have rust on the strings through being stored in a high-humidity environment. This can mean that oxidation can build up between the string itself and the bearing points (e.g. pressure bar, agraffe or the coil itself on the tuning pin) so that instead of the string sliding smoothly, it "catches" on the rusty surface and then breaks. This can sometimes (not always) be overcome by taking the string down in pitch before raising it. Of course the rust can also just weaken the wire to the point where it snaps anyway.
It is also possible, but less common, for pianos with no visible rust or oxidation problem to break, which may be due to defective manufacture of the wire; sometimes the wire seems to get "fatigued" on certain pianos for no especially obvious reason. Occasionally you can get several breakages on the same part of the same piano, which is likely due to the batch of string that was originally used.
How are strings replaced?
A competent piano technician should be able to replace a broken string for you. I normally make a special visit since there are around 20 gauges of steel wire commonly used in pianos and it's not practicable to carry them around on the offchance they'll be needed - however I do keep commonly-used gauges in stock at home. I will measure a broken string with a micrometer to find the correct diameter, then bring wire of the correct gauge with me.
Piano string comes in half-kilo reels
Bass strings (with copper windings) are a special case since they cannot be replaced with generic wire - the string must be specially made to order by a string maker which is much more expensive (commonly around £25 each).
Breakages are most common on the treble strings, where the wire is at a tension closer to its theoretical breaking strain than in the tenor and bass; but strings can break in any part of the piano.
Replacing the strings involves carefully winding out the tuning pins and coiling a new piece of wire onto the them. Replacing a treble string, or fitting a new copper-wound bass string, is usually reasonably straightforward, but if the note is in the tenor area of the piano, where the steel strings normally extend underneath the bass strings (overstringing), it can be a longer and more fiddly job.
If a string on your piano breaks whilst you are playing, save the old string since the piano technician will need to measure it to find the correct replacement. If it has been lost, then its dimensions can usually be estimated by measuring the strings next door to it.
Do piano tuners normally charge for replacing broken strings?
Must tuners (myself included) will normally charge for replacing a string because it's part of the normal ongoing maintenance of your piano, and not something that can be avoided completely however skilled the tuner is. In instances where there is a high risk of breakages (such as pitch raises on pianos that have not been tuned for many years, or where there are rusty strings), I will normally mention this risk at the beginning. The charge for bass string replacement is greater because of the cost of ordering the strings.
Feeling the stretch
Another issue when replacing the strings is that new ones will invariably stretch appreciably after being first fitted, so it may take some time for the tuning to stabilize on the affected note(s). This can be alleviated (but not eliminated) by using a string stretcher, which is a tool with a small wheel that can be run up and down the string. This "pushes" the wire and causes the stretching process to take place more quickly. Unfortunately this method can't be used on the copper-wound bass strings.
A string stretcher (right) with a coil lifter and stringing hook, two other tools used in restringing
Anyway, the video below really has nothing whatever to do with broken strings but I thought that as Franz Liszt got a mention it would be an appropriate segue into my favourite four-hands rendition of the Second Hungarian Rhapsody, performed by Victor Borge and Sahan Arzruni: