On 26/03/2012 19:59, dennis@home wrote:


"Jules Richardson" wrote in message
...

For commercial discs, I think the data is engraved into the transparent
plastic disc;

They make a master, probably from glass.
Then they metal plate it to make a negative image in thin metal.
This is used as one side of the press, the otherside being flat.
The disks are pressed between and come out with the pits, etc.
Then metal is deposited on the pitted surface to make it reflective.

Yes, that's it. The laser shines right through the pressed layer to hit
the pits; the shiny stuff is on the side with the writing, and just
under it. It's wrong to say "the data is on the pressed side.
The laser shines through the pressed side."


the reflective surface is then pressed onto this (and
carries no information on its own), then a lacquer layer goes down to
protect the reverse side of the reflective surface, then finally artwork
is printed on top of that. The laser shines through the transparent disc,
with the beam disrupted by the engraving.

There isn't really a "data side" as such because it ends up in the middle
of the sandwich:


The data's damn near the writing. Be careful when labelling your discs.

Well there is as you can't generally read them through the printing.


Screen-printed artwork / text
Lacquer
Reflective surface
Engraved data (on top surface of transparent disc)
Transparent disc
[laser shines from this side]

I'm not sure how this process differs when it comes to home-writable
media, however; presumably there's a layer of magic between the
transparent disc and the reflective surface (and bugger knows how
rewritable works! :-)

You make a blank with just the tracking on it.

"Wobble track". Except Google doesn't seem to know the term. There's no
data.

Then you cover it with a dye layer.
You burn the dye to put data on.


With re-writeable you use a phase change dye and different laser powers,
you can erase it by changing to a reflective state and then burn it by
making the "pits" using a different laser power. I forget what materials
work best.

Opinions vary on the material. If you ever get trouble try a different
brand.

Andy.