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During WW2 the boys on the front used this blue razor blade idea that Cornell came up with
to listen in on the news and music.
Gillette came up with an idea to blue coat his blades similar to gun bluing to keep them from rusting
and as it turns out they rectify because of it with the combination of the carbon pencil lead.
Must have been a stroke of genius on Cornell's part to think of such a wild idea.
In practice the way it works is you move the pencil lead over the lettering and the stations start coming in
and it just about works like a galena detector of the 1910 era because when you move the lead around you
can sometimes change stations or make the one you want clearer.
I personally built the blade radio in 1957 and again in 1962 for an electronic class project.
When I went to the Library one day i was looking around at electronic books and ran onto
a book on how to build the razor blade radio. could have been written by Cornell I don't know
I latched onto it and knew I could build it, it was fun!
My findings and rating on this type of crystal radio
1. Although it all works the stations are not as loud as with a crystal diode such as a 1N34A.
2. Tuning is not sharp because of its low Q factor and stations are sometimes bunched up.
3. So really this is a demonstration radio to show what can be done with almost nothing to listen to close powerful radio stations.
Things needed to complete this radio
1. 100 to 200 foot antenna depending on how close you are to the radio station.
if your station is real close you can connect up to almost any metal and get a signal
2. A pair of high impedance headphones 2000 ohms or better.
3. A ground connection to a cold water pipe made of metal.
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American Made 
