As mountain dulcimer players, we have a tendency to fall into the rut of playing almost exclusively in the key of D, no matter the key in which the song may have originally been written. But old time fiddle players pride themselves on knowing the original key of all the tunes and play in C, G, D, A at the drop of a hat. I am posting the tune Barlow Knife in large part because I like the tune, but also because it is a "G tune" -- meaning a fiddle player would never consider playing it in any key except G because that is the key in which it was written.
While originally developed in England in the 1600s, the barlow knife is considered the all-American pocket knife. George Washington carried a barlow. Mark Twain referred to barlows in Tom Sawyer and Huckleberry Finn in 1876. The small pocket on Levi's jeans (where I now keep my picks) used to be called the barlow pocket. Presumably, the composer of this tune enjoyed his own barlow knife so well that he wrote a tune for it.
If you have not tried re-tuning your dulcimer, this is a great way to start. Re-tuning to the key of G from the popular DAD tuning is very simple -- lower the middle string from A down to G. (If you play in DAA, you will need to lower the middle string from the note of A to G and the melody string up from A to D.) This tuning provides nice drones that allow you to play on the melody string only without chording (unless you want to add chords, of course). Barlow Knife is a peppy tune, but because it was intended to be played for dances, there is no need to rush the tune. The tune has three parts, and, as with most fiddle tunes, it is played AABBCC.
As a side note, the DGD tuning is referred to as the "reverse Ionian" mode. If you have tablature that is written for DAA (the Ionian mode), you can play the melody line of your DAA tab (not chord positions on the middle or bass strings) in the DGD tuning, and you will be playing those same songs in the key of G.