Erasing a CD-RW is done by heating the amorphous material
to above the crystillisation temperature, at around 200
°C. The phase-change material does not melt at this
temperature so the atoms cannot randomly rearrange, they
instead re-create the ordered crystalline structure. The
laser must sustain the crytallisation temperature for
a long enough period for the process to fully occur, so
erasing takes longer than writing.
Erasing is usually done by dragging
the “erase laser” over the entire length
of the data track regardless of whether there are amorphous
areas or not. This ensures that a full and even blank
disc is created.
