You are feeling bored for 2 reasons:
- You are not practicing the piece with CONCERTED FOCUSED EFFORT at a very slow speed, you are just going through the motions.
- You are not looking at the big picture, you have no set goals for this part of the practice.
To remove these 2 constraints:
- set goals for everything. ie: I want to master these 4 measures of music PERFECTLY at metronome speeds of 30BPS, 40BPS and 50BPS today. Tomorrow I will start from 40BPS and move to 50BPS and end at 60BPS. The goal is 120BPS and I will attain it in 7 days and I have a written plan EVERY DAY to get to that goal at every practice session and day for the next next 7 days. During the time I am reviewing all parts of the music that I want to play and by the end of the week place the chunks together into one song.
- Mindless practice means just that... you are not engaged, which means for the most part, you are bored and more importantly, wasting your time. If you do a practice PROPERLY, you should feel slightly (or more) mentally fatigued by the time the practice session is over.
80% of playing is in the head, 20% in the hands. What is on your mind as you play so slow? If it's ANYTHING else other than the goals in front of you, it is mindless and a waste of time.
Why isn't it the mechanics of the part you are trying to master? Do you feel each finger hit the EXACT note for the EXACT duration? Is your fingering correct? Is your intonation correct? ARE YOU SEEING THE BIG PICTURE CLEARLY? Meaning, do you have a clear and defined path to success?
Now, is it OK to do mindless practice? For sure! I do it when the goal is NOT to learn a piece of music but when doing exercises, because my mind is focused on doing the exercise that I have been doing for 40 years BETTER and FASTER. That takes very little focus on the music, but it takes concentration and effort to feel the limits of your fingers and push them past that, push past the burning sensation when you have done arpeggios for 30 minutes and your forearm feels like it's on fire. Focus on the lactic acid building up in those muscles and push past the discomfort for brief periods of time. The next day, its not the fingers that are the limitation but your mind and focus ON THE MUSIC.
"Chunking" is a great technique, breaking down the parts in to harder and easier parts and focusing on the hard parts until they become the easy ones is a great goal.