Steve came up with a great idea yesterday: copper washers!
Copper is a number of times more conductive than stainless steel (or even zinc, as we're not sure if any of our many different washers are electroplated steel) so it makes sense that copper washers would give a better connection.
When I suggested that the steel is needed because of the magnets in the bases of our playing pieces, his response was as brilliant as it was succinct: glue a steel washer to a copper one! This not only allows the piece to be pulled up by the magnet, but also adds a bit more "bulk" to help press the washer down onto the contact(s). Perfect!
So I just tried this with a dab of superglue to hold the washers together (I just learned, only ever use a dab, not a big splodge: ripping a superglued copper washer off the end of your finger is painful). And the result...
The values displayed tell us that a contact on column three has been activated. The most significant bit of the value being returned tells us is the contact has been made (zero) or released (one) resulting in the values of 0x03 (contact made) and 0x83 (contact released)
Sadly, not much difference.
The washer still needs to be forcibly pushed down in order to create continuity between the two parts of the contact. Even after scrubbing the washers with wire wool (to make sure there was no protective coating on them) the result was the same.
It looks like the washers idea is suffering from the same problem as the keypad membranes: it simply requires too much downward force to make a mechanical connection between two parts of the contact. Time for something else...?