Harmonics are fun sounds to produce. They can be quiet and bell-like, as on an acoustic guitar, or they can be loud and squealy, as on an overdriven electric guitar.

List of natural harmonics

These will be explained shortly.

• 12th fret: octave above open string
• 7th or 19th fret: Octave plus a perfect fifth above open string
• 5th or 24th fret: Two octaves above open string
• 4th, 9th, or 16th fret: two octaves plus four semitones above open string

There are more harmonics than these, but these are the easiest to produce and the most audible. They are ordered from lowest to highest in pitch.

Natural harmonics

Natural harmonics are the easiest to produce. A good place to begin is the 12th fret of the first string. With your fretting hand, lightly touch the finger against the string directly abovethe 12th fret. Do not hold it down, just touch it. Then strike it with your picking hand, and immediately release the string with your fretting hand. If executed properly, the result should he a high-pitched, ringing E. It will be the same note as pressing against the fret will produce. Try it again at the 7th, 5th, and 4th frets, as in the list of natural harmonics: each will produce even higher sounds, much higher than can be produced on the guitar without using harmonics! However, each will also be quieter, so the higher harmonics may be nearly inaudible without overdrive.

Pinch harmonics

A.K.A. Artificial Harmonics (though there is really nothing artificial about them). This is an advanced technique and was popularized by Billy Gibbons, Zakk Wylde, and many others as early as the 1970s including many Heavy Metal artists. These harmonics follow the same principles of physics as a natural harmonic, the difference being how the harmonic is produced. In this case a note is struck in a downwards motion with the pick and in the same motion the string is touched(one might really say brushed) with the edge of the thumb that is holding the pick.

Pinch harmonics are most effective and audible using an electric guitar with overdrive or distortion and in some cases these harmonics are virtually inaudible using a clean(not distorted or overdriven) electric guitar or an acoustic. It can sound good when used properly even without much overdrive(Billy Gibbons is the master of low overdrive Pinch Harmonics) but it's not always clear or detectible. Use overdrive or distortion for best results especially while learning and practicing this technique.

With regards to difficulty: this technique, although rewarding, is mostly rewarding only in advanced situations (soloing and intense expressive riffing). It is difficult enough to easily frustrate a beginner and some intermediate players and since there are so many more rewarding and useful techniques worth spending time on as a beginner(scales, soloing, blues, riffing, strumming patterns), this technique is only recommended for intermediate or advanced players.

As mentioned above these harmonics are produced by striking a note with the pick and touching the string with the picking thumb. Grip the pick so that the tip barely peeks out between your fingertips(this is why they are called "pinch" harmonics). It's easier when you are fretting a note with the left hand so try fretting a note (perhaps the 5th fret on the 4th(D) string), and plucking the string just below the neck pickup pole pieces (maybe 1/8" toward the bridge from the pole pieces). With luck the artificial harmonic will ring, but if not don't despair.

The position of the plucking along the length of the string is one of the most important parts of this technique. While with regular picking the position of the picking along the string can make slight variations in the sound of the note, when executing pinch harmonics the right position is vital and tiny positional differences can make entirely different harmonics. So try adjusting the picking hand just millimeters up and down the string around the area of the pickups.

Try imagining the pick and your picking thumb plucking the string at the same time although the thumb is really just brushing past it. Consider it to be really one motion. Try thinking of your thumb and the pick as one entity and instead of picking straight down, pick down and a little bit(millimeters) out away from the face of the guitar so your picking motion is a sort of 'letter J' out from the face of the guitar and so the thumb brushes past the string and remember that the thumb should only touch the string for an instant just like the pick does.

This technique requires practice. Try executing pinch harmonics while fretting different notes and by striking the string in slightly different places all around the pickup area of the guitar. Many kinds of harmonic ringing sounds may be produced.

Without a pick, this technique may be simulated by plucking the string with the fingertip and lightly touching it with the fingernail, but this is even trickier and not very useful in practice.

These harmonics, as opposed to natural harmonics, end up being much more practical to use while playing and when mastered can be used boldly like Zakk Wylde making the harmonic part of the riff, or subtly and possibly unintentionally to add color and character to the notes or chords while playing almost anything.

Pinch harmonics can easily and effectively be combined with other techniques, such as bending or vibrato.

To hear pinch harmonics in action check out the following:

• Ozzy Osbourne's Ozzmosis(and several other albums) features Zakk Wylde who is the king of pinch harmonic with masterful vibrato so check out Track 6 Tomorrow from 1:20 to 2:00 ... I count 5 awesome pinch harmonics of different notes in that clip.
• In the movie Rock Star at the beginning, the lead guitarist in Blood Pollution (the Steel Dragon cover band) is "not hitting the squeal". The squeal they're speaking of is a pinch harmonic (and is actually Zakk Wylde playing the squeal since he's in the movie).
• One of the best examples of a bend and a pinch harmonic is Judas Priest's Lochness off the album Angel of Retribution at about 1:10.

Don't despair if you can't get harmonics as clear as Judas Priest or Zakk Wylde, they've got equipment made just for making sounds like that. Some pickups pick up pinch harmonics better than others and Judas Priest and Zakk Wylde both have EMG pickups, which are one of the hottest pickups. Hot pickups(EMG, Duncan JB, Duncan Live Wire, Bill Lawrence 500XL, etc.) do an excellent job of picking up pinch harmonics. They both also have expensive high gain amplifiers. Try this stuff out at the local guitar shop if you want a taste(warning it's easy to get spoiled/hooked!).

Tapped harmonics

This technique, like tapping itself, was popularized by Eddie van Halen. Tapped harmonics are an extension of the tapping technique. The note is fretted as usual, but instead of striking the string, the string is tapped at one of the frets listed in the natural harmonic list. Do not hold the string down with the tapping hand, just bounce the finger lightly on and off the fret. This technique can be extended by fretting a note, then tapping relative to the fretted note. For instance, hold the third fret, and tap the fifteenth fret, for the twelfth fret harmonic, because 12+3=15.

Other techniques

A final technique is a sort of combination between the natural and tapped harmonic techniques. Fret the note normally, and place the picking hand index finger on a natural harmonic relative to the fretted note (just as in tapped harmonics). Pluck the string with another finger and release the index finger, just as if producing a natural harmonic. (Courtesy of Wikibooks)