Pure tungsten electrodes (AWS classification EWP) contain 99.50% tungsten. These electrodes provide good arc stability for AC welding on aluminum and magnesium. Their color designation is GREEN.
2% thoriated tungsten electrodes (AWS classification EWTh-2) contain 1.70 to 2.20% thorium. They are the most commonly used. Unlike pure tungsten, these electrodes are exceptional for DC electrode negative or straight polarity on carbon and stainless steels. Their color designation is RED.
2% ceriated tungsten electrodes (AWS classification EWCe-2) contain 1.80 to 2.20% cerium. These electrodes perform best in DC welding at low current settings but can be used in AC or DC processes. Their color designation is ORANGE.
1.5% lanthanated tungsten electrodes (AWS classification EWLa-1.5) contain 1.30 to 1.70% lanthanum, or lanthana. These electrodes have many of the same advantages as ceriated electrodes. They also closely resemble the conductivity characteristics of 2% thoriated tungsten. Their color designation is GOLD
Zirconiated tungsten electrodes (AWS classification EWZr-1) contain 0.15 to 0.40% zirconium. It is ideal for AC welding and under no circumstance is zirconiated recommended for DC welding. Their color designation is BROWN.
Each of these electrodes placed side-by-side look identical. For that reason a color code system has been developed to designate each. Short of sending them to a lab for analysis ($$$) once the color designation is gone, there is no way to tell what type of tungsten you're holding.
As the hack Tig (GTAW) welder I am, I keep short, unmarked tungstens in old military stick match containers. Each container is clearly marked as to the type of tungsten inside. Along with that, I always-always-always break down my torch when I'm done and store the tungsten in its designated container.
This works for me in my garage. This would not be a good practice in a manufacturing or code environment.
Once the marking is removed the tungsten is not traceable and you just lost control of your weld process.