You played slide guitar on Corrosion of Conformity's "Stare Too Long," from the 2000 album America's Volume Dealer. How did that come about?

I had gotten a call from Pepper Keenan saying he had a song he'd like me to play on. I listened to the song, and really liked it, and we went into the studio in New York and recorded it. I really loved that song from the first time I heard it, and I think that song should have been a big hit. I think Pepper felt the same way.

You didn't see working with them as particularly different from what you usually do?

My role on that particular song was just to be myself. And I've been lucky that way. Aside from the time I spent in Nashville grooming myself to be a studio musician -- a short-lived process -- aside from that, I've been fortunate to have the opportunity to be myself throughout my career.

You've probably done it all as a guitarist, in terms of styles of music you've played and the kinds of experiences that anyone that's a guitarist could dream of having. What keeps that an interesting instrument for you to play these days?

I think the guitar is something you can be inspired to play for a lifetime and never feel like you've even broken the surface of possibilities. I also consider myself fortunate to concentrate equally on songwriting, singing and guitar playing. So if I ever feel like I'm less interested in one or two of those things, I always have at least one of them as an inspiration.

Is it true that you got the Dead to cover "Nothing Else Matters" by Metallica?

That was actually Phil Lesh's idea. It came about as a suggestion from his son Graham. I'm glad you pointed that out, actually, because a lot of people, because I was asked to sing it, assumed that I was the one that suggested it, but that was not the case. When we covered Linda Ronstadt's version of "Desperado," that was Mickey Hart's idea, but he asked me to sing it, which I was honored to do. It's a shame we only did "Nothing Else Matters" once, because I think we could have done it better, had we done it more than once, but I don't think it ever happened again. A lot of songs, especially cover songs, only get played once on Dead tours.

For the new Gov't Mule album, Shout!, what inspired you to approach all those other singers to reinterpret those songs for the second disc of the release?

Well, we didn't start out with that concept. We went into the studio thinking we were making the next Gov't Mule album with no guests. I had written a song called "Funny Little Tragedy" that reminded us of early Attractions, or the Clash, or something from that era. I sent Elvis Costello an email about getting his advice on getting an era-specific vocal sound for that recording because we had never recorded anything like that before.

His advice to me was to use a very cheap microphone because that's what they did in the early days of that music, which I did, and I called him back to thank him. From that point forward, I had started thinking about him singing that song. We had a similar experience with "Toots" Hibbert from Toots & The Maytals and thinking about him for a song called "Scared to Live," and about Dr. John for a song called "Stoop So Low."

Those were the first three people we thought of. Initially, we were just going to have them sing a small cameo appearance, but that seemed a waste to have singers of that stature sing such a small part, so we decided to let them sing the whole song. Once we made that decision, I thought it would be nice to just go through every song and make a list of who, other than myself, I'd love to hear sing it, and that's what we did.

You have Grace Potter singing "Whisper In Your Soul."

Grace and I go way back. She came on the road with Gov't Mule several years ago, and we've toured together several times. We've shared the stage a lot. That song seemed to work from a female perspective, as well as a male perspective. So I thought it would be nice to include Grace, and, of course, she did a wonderful job.

Blues has had a kind of resurgence in the last few years. What do you think keeps that a relevant form of music through to today?

The blues is timeless music. It may come and go, as far as mainstream popularity is concerned. The music of Robert Johnson, Son House and B.B. King and Freddie King and Albert King and Howlin' Wolf and Elmore James and Muddy Waters is going to be around as long as there's music. That music is where rock and roll music came from.

I think it's important that young musicians and artists keep the blues alive, but the blues will keep itself alive to a certain extent. I think the times that we feel like blues music or blues-inspired rock and roll music is less popular seems to coincide with the times when the people doing it are less inspired.