Then the mylar is laid down on the glass and stretched. I used a stretching jig made up with a wood frame and screws, but you might get away with just flattening out the mylar with tape and tensioning it up later by heatshrinking it with a heat gun. A TINY amount of graphite is then rubbed hard into the mylar until it is scratched up and grey. You can measure it's resistance with a high-ohms meter, but is not critical. Rub off any excess with a clean cloth.
Any loose graphite means hiss in the earphone.
There needs to be an electrical connection to the diaphragm, so here I placed a piece of brass shim about 4mm wide down on the mylar, this will be sandwiched between the mylar and the stator and will be able to be soldered to. You could also use copper tape or maybe aluminum foil - it would be fragile. I have also had success with just leaving a small tag of the diaphragm hanging out of the assembly and connecting to it by pressing a brass shim contact against the graphite treated side. Glue the stators on top of the spacers, then squash the lot flat with something heavy and flat like another piece of glass. It is important that they cure flat.