CD-ROM technology 2
  Wikipedia topic : optical disc drive

  On commercial CDs, DVDs, Blu-Ray discs, pits and lands achieve differing 
    reflected brightness through destructive or constructive interference. 

  Commercial disks have physical pits. The coherent waves of laser light 
    reflects differently off of a pit and off of a land. 

    A pit is ~ 1/4 wavelength deep. 

    As a result, reflected laser light tends to amplify or cancel out 
      depending on the distance from the reading laser.
 
    Commercial CDs are physically stamped.

    
     source : wikipedia.org

  Commercial Worm use high powered lasers to physically modify recording
    surface. Pit scatters light rather than reflect.

  Home burned disks use a strong laser to burn a spot in a dye coated disk.
  (www.cd-info.com and www.cdrfaq.org)

  Disc layers.

  
    Source : en.wikipedia.org/wiki/Compact_disc

    A. poly-carbonate disc. 
      If commercial compact-disk, stamped with to create pits and lands.

    B. Reflective layer. On commercial disc, follows contour of poly-carbonate.

    C. Protective layer (lacquer)

    D. Possible artwork and extra scratch protection.


  CD-R layers - burnable/recordable discs.

    Label (optional) and scratch resistant coating (optional) (D).

    UV-cured lacquer  (C). 

    Reflective layer - CD-ROM.  (B).
      Aluminum - commercial CD-R

      Gold  - real gold.

      Silver - proprietary (secret).

    Data layer (B') - rather than indenting poly-carbonate, additional dye
      layer that can be denatured to change transparency.
        Clear - land - laser reflects off of reflective surface.
        Dark - pit - absorbs laser causing dark spot. 

      Dyes - organic polymer.
        Cyanine dye - cyan blue. (or Green) 

        Phthalocyanine dye - faint aqua tinge.

        Azo (Metalized and other) - dark blue.
  
          See : en.wikipedia.org/wiki/CD-R 
            There is a section on dyes.

        Without finding the manufacturer and lot number, it is very difficult
          to determine actual dye used.

        Current DVD mfgrs. may also use a variety custom dyes (based on Azo?).
          Formazan - Kodak blend of cyanine/phthalocyanine.

        Some Writable Blu-ray may use a different technique/chemical reaction
          to record "pit" which may be more stable.

        * No way to prove endurance.

    Poly-carbonate substrate (main body of disk). (A)

      CD-R - pre-grove - spiral groove with a wobble to help lasers track 
        while burning data and provide time for correct speed of disk. 

        Pre-grove also has data about manufacturer, disc type (r or r/w), dye, 
        spiral length in blocks, rated speed, and type (audio or data).


  Quality of recording affected by choice of media and drive manufacturing.

  Also, older 16x speed cd-r drives may not be able to record on cd designed
    for the newer 48x writers.