How much should i tip my tattoo artist?

I am getting a tattoo. After many years of waiting I am finally doing it. I am wondring what I should tip the artist. His rate is $100 per hour, and he is regarded as one of the best artists in town. It will be initial session will be 1 hour or so.
Since I have never dealt with tipping anyone in this line of work, what percentage would be appropriate? Would I tip like I would for a nice dinner 15-20% or is that too much?
Help… Im confused :confused:

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