Prolific avant-garde composer Philip Glass will be dropping by the Corcoran Gallery of Art this evening at 6:30 to discuss his life, career, and four-decade friendship with Chuck Close, a tie in with the traveling exhibition Chuck Close Prints: Process and Collaboration, which closes Sept. 26. In this, the second part of our phone conversation with Glass, we discuss musical portraiture and how one lifetime might not be long enough for you to witness a paradigm shift in music. Read part one first, or it’ll be like trying to drop into Sons of Anarchy with the new season. (Kidding. I’ve never seen Sons of Anarchy. Even though I want to. Rollins was on it.)

But seriously, read part one. This will still be here when you get back.

We talked about how Chuck Close took your photo in 1969 and used that image as the basis for many, many portraits of you. In 2005, you returned the favor, writing a piano piece inspired by Mr. Close.

A couple of pieces, yeah. I said, “Chuck, I’ve got these two pieces, and I’m not sure which one is you.” He listened to them and said, “I like ‘em both!” So I don’t know. Those are funny things.

How do you go about making a portrait in music?

I know of one other person who did portraits of that kind. Virgil Thomson used to do portraits, but he did it in a very different way: He would have the person sit in front of him, and as he watched them, he would write the music. That was quite an interesting exercise. I didn’t need to do that; I knew Chuck quite well by then. I could summon his image up in my mind without any trouble, and it really wasn’t a pictoral exercise anyway. So I don’t know what Mr. Thomson was thinking, but that’s how he did it.

I read in the New York Times that there was a mixup where your assistant sent the wrong version of the Close portrait composition to Bruce Levington, the pianist who’d commissioned it. And after Mr. Levington heard both versions, he urged you to combine them one after the other in what became the final piece.

Oh, yes, that happenened, too. I forget which was the right one. It didn’t really matter. When Chuck did a picture of me, it was very specific. His portraits are a reflection of the person, which has undergone a very special technique and way of looking that he has evolved as a painter. My relationship to Chuck as a subject was more subjective: You wouldn’t listen to to the music and say, “Oh, there’s that guy.” But then, maybe you would!

[The 1898 orchestral composition] The Enigma Variations by Edward Elgar were portraits of his friends. He knew who they were, but he never told them which variation belonged to which person. He left it up to them to guess on their own. It was a puzzle. He made a puzzle using his friends, and he let them decide who was who. Hilarious, huh?

Did he eventually tell them which person had inspired which variation?

No, he never divulged that. I recently did a composition called The Four Seasons, but I didn’t tell people which music belonged to which season. It was more interesting to see what other people thought.

Does it matter to you whether the listener makes the same connection between the season and the piece that you did?

No. It’s far too subjective.

You’ve said that what you and Mr. Close share is that your art “comes out of an exhaustive and detailed process.”

That’s very true. One of the things we trying to do was to resolve the problem of content versus form in a fresh way. When I wrote a piece like Music in Shifts, the technique of the piece and the tone of the piece and the content of the piece were identical. So it was a way of conflating that.

The first paintings like that would be when Jasper Johns did the American flag. Is it a painting or is it a flag? Is the content the form, or is the form the content? Taking a very radical point of view about that allowed painters, and musicians for that matter, to change the conversation about what art was about. That’s what that generation did.

Is that something every generation of artists ought to do, or aspire to do?

No. In music, it happens very rarely. The rate of change in music is glacial compared to art. It takes about 50 years, maybe three generations. And then only a handful of people will do it, and that might not be acknowledged for 20 years. It was only when I was in my fifties and sixties that people thought maybe what I was doing should be taken seriously. When I was in my thirties and forties, very few people paid any attention to it.

In the world of painting, it’s quite different. Almost every 10 years [there’s a shift]. In your lifetime, you can see new things coming up all the time. In the world of music, in one person’s lifetime, it’s like waiting for Hailey’s Comet: You might see it, but you might not. You might not see it at all.

Do you envy your visual artist friends that — the more rapid rate of change in their medium?

My generation was in fact the generation that did do that. We changed the conversation about music. That’s why we got into so much trouble. Music is a much more conservative enterprise than painting.

What music do you listen to for pleasure?

Mostly music that’s not from here. It’s what people call “global music.” It could be from Africa or India. I like things that have a very different sound to them. I’m completely involved with melody, harmony and counterpoint all them time, from morning ‘til night, so for listening I like to find something quite different. Some of my favorite singers are from South India. I became very good friends with Ravi Shankar when I was his assistant for some years. That lead to a whole, long exploration and involvement with that music.

Tickets to Philip Glass’s talk tonight at the Corcoran cost $25 ($20 for museum members, $12.50 for students); the price includes admission to the long-running traveling exhibition Chuck Close Prints: Process and Collaboration.