I believe that the coating is carbon powder.  I have no idea how they
get it on..  You could probably pull the carbon rod out of a dry cell
and powder it with sandpaper.  Put some kind of adhesive on the rubber
and dust the powder on.  There are also some conductive epoxies and the
CircuitWorks conductive ink pen.

One thing I know will work for sure is the thin adhesive backed copper
foil that is sold for wiring in dollhouses.

Lee Jones wrote:

> Hi all,
>
> I'm looking for a small quantity of conductive coating to
> repair a rubber membrane keypad.  I got some oil between
> the rubber membrane and the PC board.  Alcohol cleaned off
> the oil just fine.  But my overly vigorous scrubbing with
> a Q-tip also removed the conductive coating on a few keys.
>
> This is the style of keypad where there are interlaced
> fingers on the printed circuit board.  Underside of each
> key is a dome of rubber with a raised spot in the center.
> The raised spot is coated with a conductive substance.
> When the key is pressed, the conductive coating closes
> the circuit by "shorting" the fingers together.
>
> Anybody know if this conductive coating is available for
> repair work?  If so, a vendor and part number would be
> nice.  Or is this material the exclusive province of the
> people who make rubber membrane keypads?
>
> Thanks in advance.
>                                                 Lee Jones