My father used to always practice music slowly. It was always a great comfort to hear him practice when I was a kid (perhaps my greatest comfort) because everything always sounded so beautiful. It didn't matter what he was practicing (perhaps therein lies my fondness for scales and etudes) and it didn't matter whether it was tonal or not.
12-tone music was the new music of choice in the 1960s and early 1970s, and I still feel kind of goofy when I tell people about the comfort it brings me to hear Schoenberg played well. I also feel a little goofy telling people how much I enjoy practicing the viola slowly. I guess that slow practice is one way to make sure that all the string crossings and shifts that you need to do, and all the pitches that you need to hear find their eventual path of least resistance. It may be "making slow progress," but in the long run slow practice accomplishes the ultimate task of playing well (when it really matters) far quicker than any other kind of practice.
I distinctly remember one week in the summer when my father was practicing a slow passage that I could not get out of my head. I also couldn't identify it. I sang it to every violist and every string player I could find (and at Tanglewood there were many), and nobody could tell me what it was.
Here it is.
I later heard it in context. The passage below comes at the 19-second mark.
One of these days the piece will fall into the public domain, and I'll be able to give you more than this image from an article by Milton Babbitt about certain remarkable measures from the Schoenberg String Trio, Opus 45. I guess this bit stuck in Babbitt's imagination as well, huh?