The lasering of iron pigments can often times lead to the oxidation of said pigments, which then results in a darker tattoo. This is always a dreaded potential side effect of any light source used for laser removal – PicoSure included.
PicoSure is the same light technology as we've always had. However, it's using very short pulse durations to greatly improve efficacy. The problem still arises that the oxidized ferric pigment is now darker and more of a challenge to remove after its conversion.
Please discuss with your physician about continuance with PicoSure and review alternative methods to remove tattooed pigment in that area, besides this light source. Options may include CO2 laser, dermabrasion, or even surgical excision.