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Why do CD-R'S have a silver bottom and DVD +/- R's have a purple bottom?

Discussion in 'DVD±R media' started by fettfan, Sep 12, 2007.

  1. fettfan

    fettfan Member

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    If the recording dye is the reason, then why do the Sony CD-R's I bought have a silver bottom and the Ty's I buy have a purple bottom?
    Is this because the MPAA won't let a silver bottom recordable DVD disc be sold?
     
  2. hobbit112

    hobbit112 Regular member

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    As I understand the reason is that the specs for the dvds calls for a different laser spectrum which reacts with the purple dye better than the silver.

    Just tossing my 2 cents in, I'm no expert on the dye business. :p
     
    Last edited: Sep 12, 2007
  3. aabbccdd

    aabbccdd Guest

    JoeRyan would hav e the perfect answer I'm sure

    Hey Joe .......
    lol
     
  4. BIGTOXY69

    BIGTOXY69 Regular member

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    fettfan- somewhat along with what hobbit112 said - It also has to do with what type of dyes are used and Reflectivity issues ! How reflective the dvd's or Cd's are ? I came to Dvd media & burning roundabouts by starting out burning cd's and over time many Trends in CDR media came and went - First they said That the Cdr's with Gold bottoms were best , that was the style for awhile !, then Silver bottomed disc were supposed to be Better ! this lasted a little while and then Platinum bottom( really shiny silver )disc were Best , The last I remember Black was supposed to the new Platiinum ? I must confess though that I have been keeping up with more of the Dvd End of media Technology lately versus CDR but I think you get the picture ? Actually The color of the disc Bottoms on CDR is often not a true reflection of the dye/dyes used as it often more of a marketing thing see above . If you Scratch most Cdr's regarless of the Writing surface 's color you will accomplish Two things One is you will probably ruin the disc ! The other is you will see that under the silver... is the actual dye color ! probably Bluish or maybe greenish/blue ? depending on the dye used ! Personally on my dvd backups If they work that's all i care about ! If I wanted them to look exactly like the originals - Silvery bottoms I would just Buy a Second copy ) fettfan I'm not knocking you or your question but as long as your DVD Burns playback properly why is the Color of the dvd's bottom important ? & no I Don't think the MPAA has anything to do with it!
     
    Last edited: Sep 13, 2007
  5. JoeRyan

    JoeRyan Active member

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    You called?

    The CD-R/RW discs require a laser tuned to produce a wavelength of 780 nanometers--at the infrared end of the visible light spectrum. The dyes that react to this wavelength at high power are cyanine (blue-green), phthalocyanine (yellow-green), and azo-cyanine (blue). The dye colors visible to the human eye can be altered by the addition of colorants in the substrate or the reflective layer. Gold was the original reflective layer, but silver alloys replaced gold because they were both less expensive and more reflective. Fooling the human eye allows the pure silver look of some phthalocyanine dyes that appear to be regular CDs. Adding very dark purple to the substrate also allows "black" discs; they look black to us because we see all visible wavelengths bounced back, but the laser only sees the infrared light coming back through the plastic. (The purple is at the other end of the visible spectrum and does not interfere with the infrared/red laser. Since green absorbs red light, there are no green substrates. This absorption property also explains the nonsense involved with using a green marker to make "better sounding" discs.)

    DVDs use a ruby-red laser that has a smaller wavelength of 650 nanometers to allow reading smaller pits and tracks that pack more data. New dyes had to be developed for this light frequency, and they all look deep purple: cyanine, azo-cyanine, oxonol. Silver is the standard reflective layer. When gold is used, its less reflective properties can cause problems.

    Blue lasers are at the opposite end of the spectrum--405 nanometers, right at the edge of the ultra-violet range. Although there is experimentation with organic dyes for blue laser discs, the ones on the market look just like rewritable media with a silver-gray look because the recording material is a combination of aluminum/copper allloy and silicon.
     
  6. hobbit112

    hobbit112 Regular member

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    So by mentioning blue lasers, those are the ones for Blu-Ray and HD discs?
     
  7. JoeRyan

    JoeRyan Active member

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    Yes. Blu-ray and HD DVD use the same type of blue-violet laser dioded, but the lenses used are different because Blu-ray requires a more expensive lens to focus very closely to the disc's surface.
     
  8. hobbit112

    hobbit112 Regular member

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    So a burner that is dual blu-ray & HD DVD thats backwardly compatable with regular dvd and also burns cds has 4 lasers? Or for switching between blu-ray and HD DVD does a focusing lens slide out of the way and use only 1 blue laser?
     
  9. JoeRyan

    JoeRyan Active member

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    Such a player will have 3 lasers: infrared, ruby-red, and blue-violet. There are several ways to get the lasers through a minimum of lenses, but the difference in numerical aperture (the focusing ability) between Blu-ray, which focuses on the bottom of the disc, and HD DVD, which focuses into the disc in the same way as DVDs, means different lens arrangements. The first Blu-ray lenses had to be expensive glass versions; HD DVD could use less expensive plastic lenses.
     
  10. hobbit112

    hobbit112 Regular member

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    Cool.

    Thanks for the info JoeRyan!
     

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