[sdiy] keyboard question

[Ian Smith]

Hi all,
I'm thinking of making a controller for my synth. I'm going to fashion it after a concertina. It's going to be a CV controller, not MIDI. I want to etch the buttonboard like a commercial keyboard to reduce the amount of rat's nest. My question is this: The black stuff that covers the contact points on commercial keyboards, what is it? where do I get it? and Is it really necessary? 
-Ian Smith
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