No, I did figure out how to have tattoos look like they're glowing, by plugging a separate texture for the tattoo into the second value of a math function node set to subtract which is in turn plugged into the ambient color.

Getting it to work with the gather node is going to take some investigating, which makes it one more thing I've got on my plate that I'd like to get done.

If it can be done at all.

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If you're joking that's just cruel, but if you're being sarcastic, that's even worse.