Bellow are some fun facts, pictures and videos related to the instruments on the album.
Scroll to the bottom for a short bibliography of sources with information about musical instruments.
Accordion
The accordion appears on "De Colores" and "El Barco Chiquitito." On both, Geol Greenlee plays what is often referred to as a "piano accordion." A piano accordion has a piano keyboard on one side and buttons on the other. Accordions with only buttons are called (surprise, surprise) "button accordions."
About The Accordion
• The accordion is a box-shaped instrument that makes sound by pushing air across reeds, making them vibrate.
• The accordion is sometimes called a "squeeze box" because the air movement is created by pushing or "squeezing" the bellows.
• The accordion was invented in Germany in the early 1800s but has roots in much older Asian reed-instruments such as the sheng and khaen.
• There are many jokes about the accordion, perhaps due in part to how loud it is. Here's one:
The difference between an onion and accordion?
People cry when they chop up onions.
Acoustic Guitar
The acoustic guitar appears on the entire album with the exception of “I Like Bugs,” and “Animal Fair” (hidden track). Sean plays a steel string guitar (as opposed to a nylon string classical or “Spanish” guitar). This type of guitar is typical of most styles of country and rock.
On most of the songs, he strums with a flat pick. He uses the flat pick to pluck a short, single-string solo on “This Is Our House” (it's the second part of the instrumental section, between the harmonica and electric guitar). He fingerpicks the guitar on “Hikin’ Blues” while Kevin Abernathy plays acoustic slide guitar. (You can hear Sean’s guitar in the rugh speaker and Kevin’s in the left.) Slide guitar is a style associated most directly with the blues. It involves putting a metal or glass tube on a finger of the hand that generally pushes down the strings. Then, instead of pushing the strings to the fret board, the slide (as the tube is called) is touched to the strings and slid from note to note. This style of guitar is one of the influences (alongside Hawaiian slack-key guitar) on the development of the steel guitar and the dobro. 
One of the most famous early slide guitar players was a Mississippi Delta musician named Robert Johnson. No videos were ever taken of Johnson since he wasn't really famous until after his death at the age of 27 in 1938. In fact, the picture to the left is one of only two photos of Johnson that have survived.
Below is a video of some fellow sitting in his living room doing a nice job of demonstrating Johnson's style of slide guitar.
About the Guitar:
• The modern form of the guitar can be traced back to Spain to as early as the 1500s.
• The idea of making a plucked stringed instrument out of a wooden box dates back centuries before that to instruments such as the European lute and the Middle Eastern oud.
• The lute and oud are thought to have even earlier roots in the Middle East and ancient Greece.
• The Spanish introduced the guitar to the New World in the 17th century, and it slowly made it’s way from Latin America into North America.
• The guitar did not become popular in the Appalachian mountains until the early 1900s at which point it became a part of early country music (then called “hillbilly music.”)
• Part of the guitar’s popularity in the early 20th century was due to the advent of mail order catalogues which enabled people in rural communities to purchase relatively cheap guitars.
• By the 1940s, perhaps largely due to the popularity of the singing cowboys in the movies, the acoustic guitar replaced the fiddle and banjo as the central instrument of country music.
• The acoustic guitar is common to many styles of music including rock, folk, bluegrass, old-time, blues, many Latin styles, and the list goes on…
Banjo
The banjo appears on the following songs: "Paw Paw Patch," "Mole In The Ground," "I’ve Been Workin’ On the Railroad," "The Crawdad Song" and "Jenny Jenkins." On most of these songs, Sean plays in the claw-hammer style – a style that predates the bluegrass three-finger style, and involves a down stroke or hammer motion instead of picking with the fingers. Can you find the song on which the banjo is finger-picked instead? 
Sean plays an open-back banjo typical of old-time music. Bluegrass banjos typically have a back, called a resonator.
Below is an instructional video showing the basic claw-hammer motion:
About The Banjo:
• The banjo is a four our five stringed instrument made out of what is essentially a drum head attached to a wooden neck.
• The first banjo-type instruments were from Africa and were brought to America or fashioned by Africans brought to this country to be slaves. 
• African banjo-type instruments (e.g. ekonting, ngoni) and early American instruments (eg. banjar, banza) were often made out of a gourd with animal skin stretched across it and cat gut or horse hair for strings.
• More modern banjos use metal strings as well as wood, metal and plastic parts (much like a snare drum) for the sound box.
• There is evidence of the banjo in Appalachia as far back as the early part of the 19th century, but it did not become a central part of Appalachian music until after the Civil War.
• The banjo was transmitted from black to white musicians in a number of ways including direct contact between black and white Appalachians and contact created by the riverboat trade, the early railroads, the civil war, the coal mines, other early industry and perhaps the traveling minstrel shows.
• Banjo styles before the late 1930s in both the black and white traditions included clawhammer (or frailing) and two finger styles.
• Downstroking styles such as clawhammer are often played in what is called “old-time music” and fit well with fiddle styles used for dancing.
• The three finger (“Scruggs”) style of playing that uses metal picks and is associated with bluegrass, did not become common until the 1940s.
Djembe
The djembe appears on “Mole In The Ground” and “Drinking Gourd.” Phil Pollard recorded two tracks of djembe on "Drinking Gourd," making it sound like there are two djembe players. The djembe, like the banjo, is from West Africa. "Mole In The Ground" begins with the African Djembe and banjo and then brings in the Europen fiddle, guitar and bass. This is symbolic of the process of early African-American musicians mixing together musical elements from their homeland with the new music they heard in America.
About The Djembe
• The djembe (also spelled jembe, djimbe, jimbe, yimbe) is a drum from West Africa that is played with both bare hands.
• Traditionally the head of the drum, which is round, is covered in animal skin. Some modern versions have a synthetic head.
• The body is shaped like a cylinder with a bowl on top.
• Their are many traditional rhythms for the djembe that are associated with music for specific occasions, ceremonies or traditions.
• The djembe is often used to accompany dance.
• It is the most popular African drum outside of the continent of Africa. In America, it is often associated with gatherings known as drum circles.
Drum Kit
The drum kit appears on “This Is Our House,” “I Like Bugs,” “De Colores,” “I’ve Been Workin’ On The Railroad,” “Peanut Butter and Jelly,” “Mama Said No,” “Hikin’ Blues,” and “Freedom Song Medley.” Steve Corrigan plays the drums with sticks on all the songs except "I've Been Workin' On The Railroad" and "Hikin' Blues" on which he uses brushes for a softer sound. 
The basic parts of a drum kit are: 1 - ride cymbal 2 - floor tom 3 - toms 4 - bass drum 5 - snare drum 6 - hi hat.
About The Drum Kit
• A drum kit (also called a drum set or trap set) is built out of all of the equipment used by a jazz or rock drummer.
• In addition to the standard parts in the picture above, some kits also include more cymbals, more toms, wood block, cowbell, and even two bass drums in some styles of rock.
• The basic components of the contemporary drum kit were standardized in the early part of the 20th century with the development of jazz.
• Most of the drums used in the drum kit come from military band drums rather than African drums.
• Drummers often use both hands and both feet to play. They use their hands to hold sticks or brushes used to hit the snare, hi-hat, toms and cymbals. One foot is used to push a pedal that swings a mechanical arm that strikes the bass drum. The other foot controls whether the hi-hat (basically two cymbals on a stick that face one another) is open or closed. 
Electric Guitar
The electric guitar appears on “This Is Our House,” “Peanut Butter and Jelly” and “Drinking Gourd.” Kevin Abernathy plays in several different styles on the album. On "Peanut Butter and Jelly" he uses a clean sound reminiscent of early rock 'n roll. His alternating solo with the steel drum on that song sounds a bit like African pop at points. On "Drinking Gourd" Kevin's guitar sound has some distortion added to it and he plays a rockin', bluesy guitar solo in the middle (kids need to rock too!). Listen for the animal sounds Kevin makes with his guitar in the second half of "This Is Our House."
About The Electric Guitar
• The idea for an "electric" (amplified) guitar was developed in the United States in the 1920s when inventors like Les Paul began trying to amplify acoustic guitars with the use of phonograph needles, telephone pick-ups and contact microphones.
• Les Paul and others continued to experiment over the next decade with magnetic pick-ups to amplify the steel strings on the guitar.
• In 1931 Adolf Rickenbacher and collaborators mass produce the first electrified stringed instrument - a steel-bodied Hawaiian guitar called the "frying pan."
• In 1936, Gibson becomes the first company to mass produce what is considered the first modern electric guitar - the ES-150. At this point, electric guitars still had a hollow body like an acoustic guitar.
• Les Paul is generally credited with perfecting the first solid-body electric guitar in 1941. He called it "The Log."
• In 1950, Leo Fender released the first mass-produced solid-body electric guitar, the "Telecaster."
• In 1952 Gibson, released a solid-body model called the "Les Paul."
• To this day, the Telecaster, it's cousin the Stratacaster (1957), and the Les Paul are still extremely popular with rock musicians.
• On a side note, besides being a guitar inventor, Les Paul was also a wonderful guitar player. Below is a video clip from a documentary about Paul. It includes some interviews, clips of him playing in more recent years, and some historical clips of performances with singers Mary Ford and Bing Crosby.
Fiddle
The fiddle appears on the following songs: Pawpaw Patch, Mole In The Ground, I’ve Been Workin’ On The Railroad, The Crawdad Song, and Jenny Jenkins. Greg plays in a typical old-time fashion that uses a “shuffle” rhythm that fits perfectly with the claw-hammer banjo style described above.
About the Fiddle:
• The fiddle is a four stringed bowed instrument - the same instrument as the violin but played in a different style.
• The modern violin dates to sixteenth-century Italy. There are bowed stringed instruments from a variety of music cultures that predate the modern violin.
• It was brought into the mountains by early European settlers along with tunes that can be traced back to folk traditions from Scotland, Ireland and other parts of Europe.
• It was the most common early rural American instrument. In Appalachia it was the primary instrument from the 18th century through the early 20th century.
• In Appalachia it has sometimes been called “the devil’s box” due to its connection to dancing and other “sinful” activities.
• Many old-time Appalachian fiddler’s hold the bow towards the middle, rest the fiddle on their chest, and tune their fiddles in alternate tunings for different songs – all very different techniques than modern classical violinists employ. Many modern bluegrass players have more of a classical approach while also integrating blues elements into their playing.
• While often associated primarily with white musicians, a strong black fiddle tradition can be traced back to plantation days. This tradition significantly influenced the styles that became associated with old-time and bluegrass music.
• The fiddle/banjo combination became the center of the Appalachian dance band by the early 20th century. There is evidence of this combination existing among black musicians for many years before it was common among white musicians in Appalachia. 
Mandolin
The mandolin appears on "I’ve Been Workin’ On the Railroad" and "The Crawdad Song." On both tunes, Sean at times “chunks” the chords in a manner that is consistent with bluegrass music. In bluegrass, the mandolin plays on the “backbeat” – beats two and four – which gives the music a syncopated feeling. The backbeat is played on the snare drum in most rock music. On "I’ve Been Workin’ On The Railroad" Sean plays an instrumental section that features the mandolin and banjo together (he, of course, recorded them at different times).
He plays this section with a syncopated feel that was inspired by some of Sean’s favorite mandolin players, Howard Armstrong and Carl Martin. Howard was an African-American fiddle and mandolin player from LaFollette, TN. Carl was a multi-instrumentalist from Big Stone Gap, VA. Together, they formed a string band with Ted Bogan in the 1920s in Knoxville, TN called the Tennessee Chocolate Drops. The Chocolate Drops played everything from ragtime to old-time, blues to pop. The three musicians reunited in the 1970s as Martin, Bogan and Armstrong and toured the world.
Howard often used the stage name "Louie Bluie." There is a festival in his honor, near his hometown of La Follette, TN, called the Louie Bluie Festival. Sean helps program the music for this festival. You can read more about Howard and the others on the festival website:
About the Mandolin
• The mandolin is an eight-string, plucked instrument that is tuned like a violin.
• Mandolins typically have four identical pairs of strings (though some blues mandolin players would string the bottom two sets in octaves.)
• Like the violin, the modern Mandolin dates back to 16th century Italy with it’s roots dating back centuries to the European Lute and Middle Eastern Oud.
• Early Italian mandolins had a round back, while American mandolins typically have a flat back. The round-back mandolins are sometimes called “tater-bug” mandolins in the United States. 
• The mandolin is a central instrument in bluegrass music as popularized by the "father of bluegrass," Bill Monroe, who mixed European fiddle tunes and styles with the blues and a hard-driving rhythm.
Piano
The piano appears on “This Is Our House,” “I Like Bugs,” "Mama Said No,” and the “Freedom Song Medley.” Sean plays piano on "I Like Bugs" and Geol Greenlee plays on the other three. The picture to the left is an acoustic grand piano. Sean's dad had one of these for a couple of years of Sean's childhood, but Sean mostly grew up with old upright pianos. Sean doesn't have either type of acoustic piano in his recording studio, so he and Geol played electric pianos that are made to sound like acoustic pianos.
About The Piano
• The piano is a keyboard instrument that is sometimes grouped in the percussion family because its sound is made by striking the strings, much like the "keys" are struck on another percussion instrument, the xylophone (see below).
• Older keyboard instruments such as the clavichord and harpsichord utilize a mechanism that plucks the strings when the keys are pushed.
• The technical challenge of creating a mechanism that would make a hammer strike the string was much more difficult to overcome. It was also a challenge to build a strong enough frame to withstand the string tension required by a piano.
• In Europe, these challenges were overcome in the 18th century and, due to it's superior expressive qualities, the piano quickly replaced the harpsichord as the preferred keyboard instrument in classical music.
• Since then, the piano has become a popular instrument in multiples styles from gospel to jazz to rock.
• Pianos are related to the hammered dulcimer, another instrument that also uses hammers to strike the strings. In the case of the hammered dulcimer, the strings are struck by hammers (or mallets) that are held in the player's hands. (Though sometimes featured in concerts with the Appalachian mountain dulcimer, the two are not related besides in name.)
• The development of the hammered dulcimer, which has enjoyed great popularity in Eastern Europe as the cymbalom, can be traced back to the Middle Ages in the Middle East from whence it travelled and became popular in Asia. These instruments also set the stage for the development of the piano.
• The hammered dulcimer is sometimes used to play Celtic and American fiddle tunes. The video below features the hammered dulcimer playing a set of Scottish tunes. It's almost as if he's playing the inside of a piano!
Steel Drum
The steel drum (sometimes called a "pan") appears on “Peanut Butter and Jelly.” During the verses Phil Pollard plays the 3-2 beat in between the vocal lines. The steel drum alternates with the electric guitar in the instrumental solo section. The pan to the right is a diatonic pan - i.e. a pan that only has enough notes to play in one key. Some pans, like the one Phil plays, are chromatic, meaning that they can be played in multiple keys.
About The Steel Drum
• The steel drum is made by hammering the top section of an oil drum into a concave shape (like a bowl).
• Small hammers are then used to carefully hammer different sections of the drum head to produce different notes.
• The steel drum was originally invented in Trinidad in the 1930s as an instrument to be played as part of Carnival, a large celebration that is part parade, part circus, part theater, and part street party. Carnival developed as a way to celebrate before abstaining from such activities during the Christian season of Lent. 
• The steel drum is now played on many more occasions than just Carnival and has become widely associated with the music from the wider Caribbean region.
• Below is a video of a steel drum band on the island of St. Lucia.
Upright Bass
The upright bass appears on all songs except "Hole In The Bottom of The Sea" and "Animal Fair" (hidden track) and "I Like Bugs" (the hidden track version). Maria Williams plucks the bass in a manner associated with bluegrass or jazz, rather than bowing it as is often done in classical music. Upright basses stand about 6' tall, while Maria stands about 5' tall, making her one of the smallest upright bass players you are likely to see.
About The Upright Bass
• The upright bass is typically referred to as the "double bass" in classical music.
• It is the largest of the four instruments in the violin family - a family consisting of the violin, viola, cello and bass (listed here from smallest to largest).
• Like the cello, the bass is too big to hold and must rest on the floor to be played. Unlike the cello, which is played while sitting with the instrument between one's legs, the bass is played standing up next to it in order to reach the neck.
• The picture to the right shows the relative sizes of the four instruments in the violin family. It also shows the pitch range of each instrument in relation to a piano keyboard.
• Like the violin, the upright bass in it's current form dates back to sixteenth-century Europe.
• Other names for the upright bass include contrabass, string bass, stand-up bass, acoustic bass, bass violin, doghouse bass, bull fiddle and bunkhouse bass.
• Among other styles, the upright bass is common in bluegrass, jazz and rockabilly.
• Elvis Presley and his mid-1950s band were early "rockabilly" pioneers. Below is a video of that band performing with Bill Black playing the upright bass.
Xylophone
The xylophone appears on “I Like Bugs” and “Pawpaw Patch.” Phil plays a type of xylophone that would typically be found in a classical orchestra.
About The Xylophone
• The term xylophone comes from the Greek words xylon for "wood" and phone for "voice", together translating as "wooden sound."
• The xylophone is a tuned percussion instruments that is traditionally made from two or more bars of wood that are struck by wood, plastic or rubber mallets. Xylophones can also have metal or plastic bars.
• A "tuned" percussion instrument is one that, when played, produces specific pitches as opposed to the un-pitched sound of instruments such as the snare drum. This means that one could play the tune of a song on a xylophone, but could only play the rhythm on a snare drum.
• The xylophone is common around the world and likely developed in multiple places at the same time. The oldest traditions point us to Africa and Asia where it is still an important instrument. 
• In Africa, xylophones are called marimbas and, in fact, many people refer to all large, wooden xylophones as marimbas.
• Below is a video of xylophones being played in a Javanese gamelan (kind of like a Javanese orchestra).
Sources
Baines, Anthony. The Oxford companion to musical instruments . Oxford : Oxford University Press, 1992. Print.
Encyclopedia of Appalachia. memphis: Univ Tennessee Press, 2006. Print.
Sadie, Stanley. The New Grove dictionary of musical instruments . London: Macmillan Press ;, 1984. Print.