The light of the tattoo removing laser penetrates the layers of the skin and seeks out the ink, which then crystalizes into a solid form.  The body then spends the next 4-6 weeks expelling these foreign ink crystals thru natural processing.  It is common to see a more vibrant tattoo a few weeks after the first treatment because the ink crystals will also work their way up thru the skin layers, making the image seem darker because the ink is now closer to the skin's surface.

Each time an area is treated, the laser penetrates the top layer of the ink.  Eventually, all layers of the tattoo will be treated and the entire tattoo will be removed.

Some tattoo ink colors are more difficult to remove than others.  Some greens and light blues can take longer.