The basic requirements for producing a good tone with the thumb are the same as with the fingers. The thumbnail has to be properly shaped and polished, you must have good strings on your guitar, and hand and arm position must be correct.

Shape and Polish Your Thumbnail

If your thumbnail is not shaped correctly or not thoroughly polished, there is no way you will be able to produce a good tone. To learn how to shape and polish your nails, watch my three-part video, How to Shape, Sand, Finish, and Polish Your Fingernails.

Be Sure You Have Good Strings On Your Guitar

Defective strings emit odd or clashing overtones that will make your tone sound harsh. Old, worn bass strings will sound “thuddy” or dull. If the bass strings have discolored spots or are no longer a bright silver color, change them.

As I explained in the first article in this series, two tests must be conducted to determine if a string is free of defects:

Test #1:

First, play the string as a natural harmonic at the 12th fret. Listen to the pitch. Then press the same string down at the 12th fret and play the normal note. Be very careful when doing this test. Be sure that you don’t press too hard (which stretches the string sharp). Also be certain your finger is landing absolutely vertically onto the string. If you land the finger at an angle, it will stretch the string sharp or slacken the string flat. And of course, don’t vibrato. If the pitch of the harmonic and stopped note isn’t the same, the string is old or defective. Toss it out and put on another. If the pitch of the pressed down note perfectly matches the pitch of the harmonic, the string has passed its first test. Proceed to test number two.

Test #2:

Pluck the string above the 12th fret and watch it vibrate. You should see a very smooth vibration pattern that is relatively free of flutters. If you see wild or irregular fluttering as the string vibrates, it is defective. Get rid of it.

Right Hand and Arm Position

If your right hand or right arm is in the wrong position, your chances of getting a good tone are near zero. Watch my video, How to Find a Good Right-Hand Position for Classical Guitar.

How to Do It

To work on producing the fullest tone possible with the thumb on the bass strings, I recommend practicing on the 4th string on the Bb at the 8th fret or the C at the 10th fret. Of the three bass strings, the 4th string is the least forgiving of bad technique in plucking a string. The Bb and C produce the fewest number of sympathetic vibrations on the other strings. As described in my previous tips on tone, these sympathetic vibrations add fullness to the sound. They can mislead the ear and make the player believe he is producing a full and big tone when, in fact, the sympathetic vibrations are only covering up a weak, thin tone.

As with the treble strings, practice at the bottom of the soundhole over the rosette. We don’t want to play close to the bridge where the sound gets bright and we don’t want to play over the soundhole where the sound gets dark. We want to develop our mid-range tone.

I recommend beginning with thumb free-stroke. When working with the thumb, be sure your hand is in its optimal position for getting a beautiful tone with the fingers on the treble strings. In the first two articles in this series, you worked hard on getting a beautiful tone with the fingers with rest and free stroke on the treble strings. We don’t want to lose that hand positioning as we introduce the thumb into the mix.

Plant the “i” finger on the 3rd string, “m” on the 2nd string, and “a” on the 1st string. As explained in the previous articles of this series, be sure to contact the strings on the left side of each fingernail, flesh and nail together. Leave the fingers planted on the treble strings to keep your hand in its normal position as you work with your thumb.

Many variables exist in the anatomy of the thumb from individual to individual. Two that affect guitar playing the most are the relative length of the thumb to the other fingers and the amount of hyperextension in the thumb’s tip joint (how much the tip joint bends backwards). The thumbnail must also be quite long to contact the string correctly.

Because of these anatomical differences, the instructions I give here will not work for a significant number of individuals. I will give additional instructions for those individuals as we proceed.

When playing a bass string with the thumb, two things must happen. First, the thumb must be placed on the string so that the string touches the center to RIGHT side of the thumbnail. I say “right side” as you are looking at your hand flat on a table in front of you. This is the opposite of the fingers. Second, the string must contact the thumbnail and the flesh simultaneously. These two requirements form the golden rule of good tone production with the thumb.

Many things can go wrong:

1. If the string touches the right and left side of the thumbnail (which means you are striking the string straight-on), the tone will be bright and thin.
2. If the string touches flesh only, the string will travel on the flesh and then you will hear a click at the moment when the string slams into the thumbnail.
3. If the string touches the thumbnail only, as you play the string repeatedly you will hear a buzzy sound. This is the result of the hard surface of the thumbnail touching the vibrating string with no cushioning of the string with the flesh.
4. Your thumbnail may be too short to touch the string at all. If the nail is just a little too short, you can allow it to contact the left side of the nail instead of the center to right side. That’s better than nothing at all. Or, bend the tip joint of the thumb slightly to make nail contact. If the nail is still too short, try a fake nail. Read my tip The Best Artificial Nail System Yet. If you don’t want to mess with that, file the nail down to nothing so it doesn’t get in the way and use flesh only.

In one way, simultaneous flesh/nail contact is more critical on the bass strings than the trebles. The bass strings vibrate more widely than the trebles and therefore produce a louder buzz than the trebles if the nail hits the string before the flesh.

But, “simultaneous” contact is not really quite the correct word. Actually, what should happen is the flesh should contact the string ever so slightly before the nail to cushion the vibrating string. This is done not by having the string slide on the skin into the nail which will produce a click, but by having the string indent the flesh and then contact the nail. We say it’s simultaneous because on casual observation it feels that way. But it really isn’t. Watch this video on contacting the string with the thumbnail.

Be sure to watch the video on full screen. Click the symbol to the right of "HD" in the lower right-hand corner after the video begins playing. Hit escape "ESC" on your keyboard to return to normal viewing.

The Secret

As I described in the article on free stroke with the fingers, the best free‐stroke tone with the thumb is produced by using what some players call a false rest stroke or what Julian Bream calls playing on top of the string or what the Segovia school describes as pushing down onto the string or pushing into the string. Playing on top of the string is very much like playing a rest stroke. The preparation looks and feels like a rest stroke.

Place the thumb on the top surface of the string and push the string into the guitar just like a rest stroke. On execution, the thumb doesn’t follow through and come to rest on the adjacent string as in rest stroke. Instead, after pushing the string into the guitar, the thumb releases the string with very little follow through. As with the fingers, when you play your free stroke with this technique, it will sound as good as your rest stroke!

To get the best tone, don’t play from behind the string. Although playing from behind the string produces a good tone and is used most of the time, the best tone is produced by playing on top of the string. Unless you are trying to produce a special effect, never play from under the string. A plucky, “poppy” tone is the result.

Caution!

Unlike using this technique with the fingers, there isn’t a limitation on speed when playing on top of the strings with the thumb. However, there is one major limiting factor in the use of this technique. For many players, playing on top of the strings with the thumb requires the hand to move slightly forward toward the floor. That will make the fingers pull up more, producing a thinner tone. However, the good news is that in the real world you would usually use this technique on passages where the emphasis is on the notes the thumb is playing. The notes the fingers play would be secondary in musical importance and intentionally be kept in the background. So if their tone is slightly thinner or less weighty than the norm, it can be considered an asset in that situation. An excellent example of this is Leyenda (Asturias) by Isaac Albéniz. Watch me demonstrate in this video.

Be sure to watch the video on full screen. Click the symbol to the right of "HD" in the lower right-hand corner after the video begins playing. Hit escape "ESC" on your keyboard to return to normal viewing.

If Your Thumb or Thumbnail is Short

If your thumbnail or the thumb itself is too short, it may be difficult to contact the string on the center to right side of the nail without changing the entire hand position. If that is the case, try these techniques:

• If the thumb or thumbnail is too short, you can try straightening or bending the tip joint slightly to achieve nail contact on the string. Or, try contacting the string flesh and nail together on the left side of the nail instead. Some players may need to use a combination of both techniques.
• If you have no thumbnail at all, or if it is just one or two millimeters long, try an artificial nail as I recommended earlier. Read my tip The Best Artificial Nail System Yet.
• Or, file the nail down to nothing and use all flesh. I think an all-flesh thumbnail tone can be very nice. If one plays with nails on the fingers and all flesh with the thumb, the bass line stands out (in a good way) very clearly from the other parts of the music.

However, when using all flesh, if the thumb is wide and fat, it can be difficult getting in between the strings without damping the adjacent lower-pitched string. In that case, when using all flesh, I recommend using the left third of the thumb tip and staying on top of the strings as much as possible to present inadvertent string damping. Watch the video.

Be sure to watch the video on full screen. Click the symbol to the right of "HD" in the lower right-hand corner after the video begins playing. Hit escape "ESC" on your keyboard to return to normal viewing.

Playing from Behind the Strings

Most of your playing with the thumb free stroke will be from behind the strings. Playing on top of the strings produces the best tone but as I explained above, can affect the fullness of the tone produced by the fingers. Play on top of the strings with the thumb when it plays notes that need to be emphasized. Otherwise, the norm is to play from behind the string. But be very careful not to pull up or outward.

Rest Stroke

Thumb rest stroke is played almost exactly the same way as playing free stroke on top of the strings. The difference is that the thumb follows through into the adjacent higher-pitched string. Angles of attack can vary from almost horizontal (on the plane parallel with the soundboard) to almost vertically down into the guitar. The more vertical the attack, the fuller the sound will be.

Those with no thumbnail find this stroke to be very natural, stable, and secure. Usually, if you don’t have a nail, it’s easier than playing free stroke. Those with big thumbs still need to be careful about inadvertent string damping. Stay on the left third of the thumb tip.

String Scraping

As I pointed out in Part 3 of this series, string-scrape noise from the fingernails is a big problem when playing on the bass strings. Not so with the thumbnail. If filed properly, it produces relatively little scraping noise on the wound bass strings. Immediately after filing/shaping/polishing the thumb may produce some scraping noise. But as Julian Bream points out, it quickly goes away as the nail is “played in”.

Don’t Do This

Whatever you do, don’t play with a thumbnail that is too short to properly contact the string but that is too long and gets in the way of using flesh only. You will hit the flesh first and then the nail, producing clicks with almost every thumb stroke. Or, you will catch the very corner of the nail producing a thin, weak tone. To eliminate those bad sounds, either grow the nail longer or file it shorter. Or, use an artificial nail.

Summary

Because of variations in thumb length, tip joint hyperextension, and thumbnail length, much experimentation will be required to find what works best for you to produce a good thumb tone. Most preferred is to simultaneously contact the flesh and the thumbnail at the center to right side of the nail. Second choice is to simultaneously contact the flesh and thumbnail on the left side of the nail. An artificial nail is a possibility. Or, forget about a thumbnail and play all flesh on the left third of the thumb tip.