Full original conversation: https://discord.com/channels/439790483494141954/1199479413897707560/1287553499084886038

A patented manufacturing method for manufacturing transparent CDs called "C-Thru Disc" exists, and is used by some discs present in vgmdb. General info: https://av.watch.impress.co.jp/docs/20021225/dtj.htm

This information is especially pertinent to add because C-Thru discs die much faster than regular CDs, and many are already failing, so knowing a CD in your collection or that you want to listen to uses C-Thru is fairly important.

Unfortunately, most CDs using C-Thru Disc do not actually have the logo anywhere. Fortunately, as far as I'm aware, no other technology exists for transparent CDs (nor was C-Thru Disc ever used for anything besides CDs), and thus, it's very easy to identify that a disc is using C-Thru, since nothing else looks like it.

Due to C-Thru being able to coexist with some other Media Formats like HDCD, there will be situations where one of the two will have to be just listed in the album notes. Not ideal, but there shouldn't be very many instances of this, and there's no better solution at the moment.