I found this old article on how the old tubes make dandy knife sharpeners. 'thought I would share it:
http://www.backwoodshome.com/articles2/brannan87.html

Take the element out of an old high pressure sodium lightbulb, it too makes a good sharpner, not as abrasive as the ceramic tube.

Never considerd that. I'll have pleanty now though!!

Thats a great idea!

Be careful with the HPS, they may explode if exposed to water.