I have a fretless classical guitar and I want to use an eBow (which works by generating a magnetic field) on it (because I want to work on intonation in microtonal systems). The only things that I need from the strings are that they will be ferrous (so they react to the magnetic field) and with proper tension for classical guitar. Which materials should I look for? Do you know a string manufacturer that sells such strings?
As you have discovered, the e-bow responds to ferrous metals such as the plain steel strings of any steel string guitar or the nickel wound strings of an electric guitar. It will not respond at all to nylon strings commonly used on classical guitars.
Most classical guitar string sets include bass strings that consist of a nylon filament core wrapped with windings made of bronze, silver, or silver plated bronze - all of which are "non-ferrous".
You might find Classical Guitar Strings wound with nickel for the bass strings, which might work well with the eBow since nickle is ferrous (which is why electric guitar strings are wound with nickle instead of bronze). The GHS Vanguard Classics GHS Website - Vanguard Classics have nickel windings around the E A D and G strings but the B and high e treble strings are nylon. If you only use the e-bow on the 4th - 6th strings, you might be able to make it work with strings such as these.
Steel (found in all steel string guitar sets) is the only material used to make treble strings that is ferrous. As mentioned in other answers, the tension required to tune steel strings could cause serious problems for a classical guitar including warping the neck or pulling the bridge off the guitar. Nickel lacks the tensile strength necessary to tune to standard pitch so you won't find strings with nickel cores or unwound treble strings made of nickel.
So the answer is, yes - you can find nickel wound classical guitar strings which might allow use of the Ebow on the bass strings, but there is no string material that will tune up under the low tension that classical guitars are built to withstand that will work with an Ebow for your unwound treble strings.
On an electric guitar, the magnetic part is the pickup, which generates a small amount of electricity because a steel string vibrates close to its poles. So, as long as the strings are not brass or any other non-magnetic metal, then sound will get picked up.
As the good doctor says, the tension of those strings may cause neck problems.Or, more likely, pull the bridge assembly off the body - it's only glued on. I've re-stuck many, and none has ever detatched itself again. A look on the tension charts available from string manufacturers will guide you to the steel strings with similar tensions for the same tuning. I'd imagine that very light gauge strings (.008) wouldn't be too far off, but I'd check before fitting.
End - the Ebow will work, but the guitar may not, due to the above.My concern is that the volume produced may not be much.
Yes, this totally exists! The reason you mustn't put ordinary steel strings on a classical guitar is just that they have too much tension, not that the material itself is somehow ill-affects the classical guitar. But it's quite sensible to incorporate ferrous material into a low-tension string suitable for classical guitar. Thomastik Infeld makes such strings. They're basically very thin stranded steel cables, wrapped in nylon tape for playability and more classical sound. The typical use of these strings is to give a classical guitar a bit more of an edge and a wider bending range, but enabling magnetic pickup/e-bow exciting is certainly also a sensible use case. And they work pretty well without frets – I actually have them on my electric fretless guitar!
In that guitar I have also installed an infinite-sustain system, so I can confirm that the e-bow priciple does in essence work. I wouldn't expect too useful a sound from that in an acoustic guitar, though.
You do not need magnetic strings - this is a simple misunderstanding. Ordinary steel strings will do just fine.
The problem you have is that if your guitar is built for nylon strings it may just not be able to cope with the high tension a set of steel strings will place upon it. Snapping the neck is a real possibility - electric guitars have a strong truss rod specifically to withstand this stress.
Read this question for some guidance.