I've had 12 PicoSure visits & 1 Q switch over 2 years and my tattoo has hardly changed. Is something wrong?

Hello, I'm trying to remove a black tattoo (10x15cm) on my forearm. I've had 1 Q switch go & 12 PicoSure goes over 26 months with very little change. It could still pass as the original. All the outlines are in tact, just a bit lighter. I had another black tattoo close to the same spot removed completely by the Q switch in 3 goes. Is there a reason why it's taking so long? Could the PicoSure not be suited to me? I go to a reputable clinic. I'm female, in my 30's, pale skin & healthy. Thank you

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