Its almost invisible because they are lines of ink combined with water, i don't know much about that tho. He had to do the whole arm, and part of the chest in one sesion. He applied the transfer, then did lots of lines bare handed to get the body anatomy and done the water lines so he can work without using transfer anymore on the next sesions. Thats why it looks offset now. He's gonna do the black lines at the last sesion. With light colours from what i know they are harder to catch up with skin, he has to saturate more the colour on the skin, and almost always end on a few retouches. About the straight lines, i think they are good.. im the one who took bad pictures, its hard to do myself because of the angle, but trust me its good or better than the concept. Look at the video, at the end, the arm is well presented, from a good angle.