DIY Potentiometer

1. Paper and salt water.

Lay out a strip of newspaper
Wet well but not until soggy with salt in water solution.
Test pot.
Note how result varies with salt concentration, degree of saturation of paper, passage of time

https://www.youtube.com/watch?v=kK94lLZV1qg

2. Butyl Rubber and friends

• Black rubber used for roofing has carbon black in it.
  Take meter and wander round sticking probes in rubber on sale and other material.
  When you find a sheet of substance that has some resistance acquire a small sample by best permissible means and cut strips to make a pot.

3. Farbic potentiometer

http://www.kobakant.at/DIY/?p=543