How to recognize a Germanium Diode

Use this schematic to test the diodes. You can easily distinguish Silicon and Germanium Diodes. Silicon diodes should read approx 0.7V and Germanium diodes should read 0.3V. A little difficult to distinguish Schottky diodes though. They should show approx 0.2V which is close to 0.3V. If you have a very stable power supply and a good meter you can distinguish this as well!

Good Luck!

^{simulate this circuit – Schematic created using CircuitLab}

Germanium diodes have a lower forward voltage drop than silicon diodes. Rig up something that puts a little current thru them, and measure the voltage.

For example, a 5 kΩ resistor in series with a 5 V supply should do quite well. The current will is limited to 1 mA, and the reverse voltage to 5 V. Neither should hurt any of the diodes you have.

Silicon diodes will have around 650 mV forward drop. Germanium will have about half that.

Note that silicon Schottky diodes have about the same voltage drop as germanium diodes. If you think there might be some Schottky diodes in the mix, then it gets more complicated.

The continuity test function on many multimeters has a "diode" setting that will tell you what the forward voltage is, from which you can infer the type of diode.

http://en-us.fluke.com/training/training-library/test-tools/digital-multimeters/how-to-test-diodes-using-a-digital-multimeter.html