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01-17-2016, 05:06 AM
SFtheGreat SFtheGreat is offline
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This time I would like to ask about pressed media.

What are advantages and disadvatnages of gold and aluminium reflective layers on pressed audio CDs.
Especially the long-term benefits such as longevity, because as we all know from chemistry classes gold is resistand to almost any kind of oxidation, so technically should last longer than aluminium.

Of course, we are talking about digital media, so the zeros and ones are not affected by the medium of storage and material used for it, so anyone claiming something will "sound better" on gold/glass/etc, please educate yourself on DAC.

Personally I have several albums pressed on gold (or at least something that looks like it), CLosterkeller - Aurum and Deep Purple - Live Encounters.
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01-17-2016, 06:13 AM
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lordsmurf lordsmurf is offline
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I've never seen a pressed gold disc of any kind -- only silvery alloys.

Gold has less reflectivity (more absorption) at the wavelengths needed on optical media. That doesn't change, be it burned or pressed.

CD = 780 nm
DVD = 650 nm
BD = 405 nm

Silver = ~98% (500-800 nm range)
Gold = ~94% (700-800 nm range)

Gold has almost a 0% reflectivity in the Blu-ray range, while aluminum is in the high 90s.

It's really just that easy.

From a longevity stance, anything that would reduce readability will make the disc entirely unreadable. For DVD, even 4-5% can mean the difference between reading and not reading. The disparity between CD and DVD is much greater (ie, worse).

The primary thought behind recordable gold media is that the reflective foil won't tarnish. Well, DVD is in a protective sandwich, and oxidation will instantly kill the dye. Do you see the ridiculousness of gold DVD recordable media now?

For CD media, this theory of tarnish is sort-of sound, but the reflectivity of the wavelength still sucks. The only saving grace is that CD lasers are more powerful, and the data grooves are smaller. But even then, the media is harder to read. This also ignores the minimally protective lacquer present on the disc, which is mostly there to stave off oxidation.

About your discs ... realize a lot of "gold" media is not actually gold. The substrate and lacquer can simply have gold coloring. It's not actually gold. I have a bunch of "gold" CD-R from around 2001, and those are not really gold. The substrate is a yellow hue, and the lacquer is a light bronze. In fact, a colored substrate (ie, plastic bottom) may cause reflectivity to be harmed. I have some of the short-lived all-black (actually deep purple) CD-R as well, popularized by the original Playstation. These discs test terrible.

Note that most all "silver" and "aluminum" reflective layers are actually an alloy (ie, mixed metals). I'm not sure what exactly is used, and it differs; I've read the patents. For best reflectivity, while still being affordable (not all gold, not all silver, not all aluminum), the metals are impure and fortified.

See also: http://www.edmundoptics.com/technica...rror-coatings/
^ This has nothing to do with media, but is a large manufacturer of industrial mirrors, often used in scientific applications. The page has some neat charts, diagrams, and dumbed-down technical information.

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01-17-2016, 06:44 AM
SFtheGreat SFtheGreat is offline
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Interesting informations.
Without the alloy's exact structure we can only trust manufacturer's that they produce high quality product.

As for golden CDs, they question is what the layer is made from, i could simply ask Takt pressing plant, or beg doctors to let me use mass spectrometer, or actually write a master's paper about it, then I could research as much, as I would want.

So, gold has slightly lower reflectivity in 780nm than silver, but is more resitant to oxidation, provided, that gold is used and not a coloured alloy.

On the charts aluminium has entirely lower reflectifity in the entire spectrum, than gold or silver.

I must ask what alloys pressing plants do use.
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