There is a problem with manufacturing recordable DVD media that is a major cause of bad media. It is one of the causes of defective media but I haven't seen it commented about on this forum. The problem I'm referring to is the manufacturing process of gluing the two discs together that are used with DVD media.

Let me first explain the issue. Since the bit size of data on DVD media is much smaller than with CDR media, it is necessary to position the reflective layer on the media closer to the laser lens in the drive. This is accomplished by sandwiching the reflective layer between two thinner plastic discs thereby positioning the reflective layer closer to the laser lens. It is necessary to use a sandwich of two thinner discs to give the assembled disc the necessary rigidity for stability of the spinning disc.

But here is the problem. It is critical that the glue layer be VERY uniform in thickness to prevent waviness of the assembled disc. Any variation in glue thickness will result in the disc not being flat. This causes the reflective layer to move up and down slightly as the disc spins. This changes the focus of the laser on the reflective layer as the disc spins which causes a serious impact on the error rate or playability of the disc. This is a major problem with DVD media. If there is any waviness of the media due to improper gluing, it WILL NOT play back reliably.

There is a way to see this that is simple to do and doesn't require any special test equipment. Place a disc on a tabletop in a room that has a rectangular fluorescent light fixture on the ceiling. Adjust the position of the disc so that you can see the reflection of the straight edge of the fluorescent fixture on the bottom surface of the disc. Slowly move your head back and forth so that the reflection of the fixture on the disc moves from side to side. The straightness of the reflection on good media will remain relatively straight as you move your head from side to side. On media with improper gluing, the straight edge of the fixture will appear wavy when you move you head, especially on the outside edge (which is also where most media errors occur.) Of all the media that I have looked at in this manner, the best ones that I have seen is 16X MCC Verbatim.