I can play Irish fiddle ornaments effortlessly, naturally, it seems, but it wasn't so in the beginning. I had lots of help from Dale Russ.
Ornaments, the extra little grace notes, help to create Irish fiddle's charm and distinctive style. An example is a quick note above the main note, then returning to the main note. In classical music the violinist clearly delineates all three notes, but Irish fiddle ornaments, called a cut in this case, are more rhythmic than sounded. The ornamenting finger brushes across the string rather than playing it firmly.
I love those little touches, and I learned them by studying Dale Russ's "Basic Irish Fiddle" on videotape when I began playing Celtic music in 1990. I studied his finger movement in slow motion and practiced those ornaments slowly to develop the necessary coordination. In concert with this study I listened to tapes of Irish fiddling to understand the placement of ornaments within the main note. It's a series of notes that can't be precisely notated, and depends on the player's understanding of the music.
If I had grown up in a Celtic fiddle tradition I would have had that sound in my head from youth, but I did not so I had to embed the style in my brain. I was playing in a community orchestra when I found Celtic music, and after a year those ornaments began inadvertently entering my classical playing. Knowing which way the wind was blowing -- a decidedly Gaelic gale, it was -- I left the orchestra and committed myself to the traditional music I had long sought.
Dale's tape was sold through Lark in the Morning, and my friend Tom had loaned it to me. Dale now offers online lessons through Peghead Nation at https://pegheadnation.com/string-school/courses/irish-fiddle/. I recommend his clear teaching and playing style for the person wanting to learn Irish fiddle.