The 'blue' you are seeing on a razor blade is a certain thickness of transparent iron oxide (rust). High temperature rust is either black or clear, low temperature is red to brown/black, so where does the 'blue' come from? 'White' light is a mixture of various colours; when this hits/enters the transparent layer you will get re-inforcement of whatever wavelength of light corresponds to half the thickness of the layer because light reflecting from the top surface is exactly in phase with light that has travelled down through the layer, reflected off the bottom surface, travelled up through it to join (and enhance) the light reflected from the top. This works with thin oil films too. Oxides are insulators. 'Blue' oxide on iron is apparently just the right thickness to create a point diode (detector for a crystal radio). You can 'blue' a thin piece of steel by carefully heating it from one end and watching the film grow. Take it away from the heat just before you have enough 'blue' (it'll keep growing for a second or two after the heat source is removed). Bye. -----Original Message----- From: Peter L. Peres [mailto:plp@ACTCOM.CO.IL] Sent: Thursday, 23 August 2001 5:12 To: PICLIST@MITVMA.MIT.EDU Subject: [OT]: http://freeweb.pdq.net/headstrong/foxhole.htm (fwd) About foxhole radios (see URL below), and how to make blue razor blades. The address bounced from hotmail. If you know where the author can be reached then please forward this. thanks, Peter ---------- Forwarded message ---------- Date: Sat, 18 Aug 2001 13:13:11 +0300 From: Peter L. Peres To: bsycmiyk@hotmail.com Subject: http://freeweb.pdq.net/headstrong/foxhole.htm Hi, I was reading your interesting page and I remembered that you can make a 'blue' razor blade by holding a normal one into a lighter flame. I think that it needs to be degreased and dried very well first. I know nothing about crystal radios but maybe I'll find the time to improvise such a junction and trace its characteristics. To blue the blade, hold one end of it and put the other end above the flame. After considerable heating some portion of the blade between your hand and the red hot other end will turn blue. This should work with other scraps of steel too. Peter -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details. -- http://www.piclist.com hint: The PICList is archived three different ways. See http://www.piclist.com/#archives for details.