grubbing around in on of my latest "treasures", I found a tube I could not identify. I breathed, I applied nose grease---nothing.

Then--by accident--I shined a flashlight on it such that light was coming from the inside of the etched area. I don't think any light was actually coming from inside the tube. rather, just enough was getting in the glass and bouncing around until it cam out thru the numbers.

I need to try this on some other tubes that are pretty much unreadable by other means.

Interesting. I've noticed that a light at a low angle to the printing sometimes works too... ie an LED flashlight from the side. Move the light around; at just the right angle, the printing sometimes show up. I suppose the light could be entering the glass and back lighting what's left of the printing...

That's my hunch, but no proof just yet.

remember for pre WW2 tubes, the marking is usually in the area of the glass above the KEY of the tube. for large pin tubes thats the two fat pins.

Mark Oppat
www.oldradioparts.net

UV light will make urine glow, a really nauseating experience if you check out your bathroom with it at night. UV makes lots of unpredictable things glow. Never tried it, but I wonder if faded tube numbers would stand out in the dark with just the illumation of a UV lamp.

I thought of UV a while ago, but it didn't work. I tried the big 4 pins down to the miniatures. It's actually rare for old inks, dyes and paints to have any fluorescent compounds in them.

A light source that does work great is a high-intensity beam, in the thousands of footcandles. The glass will be largely transparent to the light but the tiny little bit of 'whatever' is there will be illuminated to max potential.

Nose grease