I'm afraid I don't have any privileged information on the constituents of Fast Fret, but the consensus online is that it is a mineral oil.
I've used Fast Fret in moderation for 20+ years and had no problems, but Max (formerly of this parish) absolutely hated the stuff. He had a lot of experiences where guitarists had used it excessively and it had formed an ugly, sticky, build up around the frets. And that would make perfect sense as the mineral oil that is used is often claimed to be liquid paraffin which could well go waxy.
I wipe the guitar neck and strings with a cloth when I finish playing and then a gentle application of Fast Fret, just wiping the applicator across the strings and not the fretboard. And I would be quite happy to concede that one of the big benefits of Fast Fret is that it makes you wipe your strings clean after playing.
However, I would like to know a little more about Williamalake's problem with his strings cutting up his fingers. Is it because he hasn't built up callouses yet? Or because his strings quickly get tarnished and build up a rough surface?
I've heard of sailors using camphor, but when I started playing I remembered that walkers rubbed surgical spirits on their feet to harden them up and prevent blisters so I used that trick on my fingertips. And have come across many players over the years who were told that trick too.
But if the problem is just the combination of environment and player's finger chemistry making the strings corrode I think there is a FAR better solution. And it will surprise regular readers....
Despite my clearly stated view that coated strings are the spawn of the devil, this is one situation where they are the ideal solution to a genuine problem. Forget Fast Fret and the alternatives... fit a good set of coated strings, keep a cloth with the guitar, and wipe down the strings and neck every time you finish playing.
Andy
