Jules Richardson wrote
Rod Speed wrote
The Natural Philosopher wrote
dennis@home wrote
The Natural Philosopher wrote

And the lacquer is a spun coated thermosetting *plastic* resin.

ITYM its usually UV setting and its really not a plastic layer
at all, its just thick enough to level the disk for the printing.

Only you dennis would print on the data side of a DVD...sigh..

All the stamped CDs do.

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

Stamped actually, not engraved.

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.

What I said in a lot more words.

There isn't really a "data side" as such

There is with the relatively thick transparent plastic that you can see.

because it ends up in the middle of the sandwich:

But not of the relatively thick transparent plastic that you can see.

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,

There is no stamping of pits into one side of the thick transparent
plastic that you can see and not metal layer either.

Those are replaced by a layer that changes when you write to it.

however; presumably there's a layer of magic between
the transparent disc and the reflective surface

It is both the layer that changes when written and the reflective layer.

The reflective propertys are change by the writing.

(and bugger knows how rewritable works! :-)

The effect of writing is reversible with those.