The ink to make it was a secret and unique process that was not disclosed even to the other elders. Surprisingly, Shen Tianyu also did not know the whole process in how the ink was created though she did know some of the materials required. This was to prevent infiltrations and potential assassinations by blending into their ranks. And this special tattoo somehow appeals to the other members' senses so they were able to identify their own even without the use of sight such as in the pathway before.
As for people that have been kicked out of Yaodu, their tattoos are destroyed by the same person or people that make them before they are thrown out.
"Should we rest or continue?" Shen Tianyu gave the option over to the others.
"Let's keep going. We didn't exhaust much energy back there, just some mental tension. But now that we have lights, I believe we should be fine." Shao Wei suggested.
