I had just had 2/4 sessions on a very large upper back tattoo. it's shoulder to shoulder and goes down to my bra strap. each one of my sessions was about 3.5 hours, and after the first 2, i was dreading finishing the piece. here's exactly how i used the product: 1. wash the area and pat dry 2. liberally apply a layer of numb master to the tattoo area and cover tightly in plastic wrap. 3. after 30 min, remove the plastic wrap and apply another liberal layer (leave on what you previously applied) and cover in fresh plastic wrap 4. after another 30 min, apply a 3rd layer of numb master on top of the previous 2 layers and wrap in fresh plastic wrap. 5. wipe off (i did not wash it off, just used a paper towel) and begin tattoo session. i paired this with vasocaine since that product is meant to be used once the skin it broken. i would say in a 3.5 hour session, i felt nothing for about 80% of the area. many parts of my skin remained numb for the entire duration. i purchased a 1oz container and i only used about half with the steps described above for a fairly large piece. 100% worth the money with no negative effect on the tattoo.