• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Question - Labeling Tested Tubes

I have my son home for the summer and he needs a project :) So, I thought about having him test tubes for a few hours each day.

I've always just used a fine point sharpie and marked each tube near the base on the glass with the gm findings. However, I've found over time they fade a little and get hard to read.

I was curious what others have been using to label tubes? Whatever method, I'd like enough room to list gm values for both sides of triodes, etc. I'm not opposed to stickers, etc., just something that is tried and proven to work well and remain easy to read.

Share your secrets... please...