Can I bit copy an optical disk that won't mount?

Thanks for the tip... but unfortunately it didn't work. If I put the non-working disk in my upper superdrive, the disk spins up and eventually Finder gives the message "The disk you inserted is not readable on this computer". I click "ignore" rather than "eject" then tried:

% dd bs=1024 if=/dev/disk4 of=./Desktop/image

dd: /dev/disk4: Input/output error

0+0 records in

0+0 records out

0 bytes transferred in 0.002291 secs (0 bytes/sec)

If I try the lower superdrive, the disk doesn't even seem to spin up and Finder says nothing. Trying dd yields:

% dd bs=1024 if=/dev/disk6 of=./Desktop/image

dd: /dev/disk6: Device not configured

0+0 records in

0+0 records out

0 bytes transferred in 0.000095 secs (0 bytes/sec)

Is the disk beyond redemption?

The disk is clean and was kept in a DVD case with cover in a glass fronted cabinet. Maybe this particular batch of DVD-R (Imation) was dodgy because others of similar vintage also fail to mount. I have other optical disks from similar era or older that are fine.

With a working DVD the dd command produces the response:

% dd bs=1024 if=/dev/disk4 of=./Desktop/image.dmg

dd: /dev/disk4: Resource busy

The disk is just sitting in the tray. No app is using it (such as DVD Player). DVD Player happily plays it if called up.

I tried both Mac Pro optical drives, my DVD player, and a drive in my PC at work. No dice. I think this disk is dead 😟

Thanks to everyone though for your helpful suggestions.