There is a big misconception that there is a large amount of blood and a lot of gore. Tattooing today is a fine line and precise art. It's not like in your grandpa's days when he got a tattoo and ten years later you can't tell what it was because it was put in so deep that the ink spread and worked its way back up through the skin.
A tattoo today, if done properly, can last without the spreading of ink. It will hold the fine line and the definition indefinitely, provided there is no damage through improper care, neglect in healing, or an abrasion fo one type or another. Depth of a tattoo may vary from one customer to another. There are many different types of skin that a tattoo artist will come across. Some will willingly accept the ink while some will totally regject it. You need to keep the skin moist and soft throughout the procedure and remember to keep the skin tight at all times. The skin is very elastic, which means that the needle can bounce or drag if the skin is not tight. The skin is made up of two layers, the epidermis and the dermis. Betweenthe two there is an approximated thickness of 1/6 of an inch. You only need to penetrate the epidermis layer to get the tattoo permanent. If you penetrate these two layers then coms the fatty tissue and after the comes the muscle tissue. If you penetrate these layers you are greatly increasing your chance of scar tissue. Fat and muscle tissue has no consistency to hold the ink. I suggest that you don't go any deepr than 1/8 of an inch. Never overwork the skin for fear of scar tissue.