What do you know about scarring as a tattoo/art form?

I am planning a large tattoo on my back, and certain aspects of the tattoo would have best results in a relief raised form, making them more prominent and three dimensional as opposed to the rest of the work.

How is this process done, what do you know about it?

How to creat a tattoo/art portfolio?

Ok. Im looking to get a tattoo apprenticeship but i need to have an art portfolio. Any advice on how i should do it? Im not much of a painter,but I LOVE oil pastels and coal. Any help would be great! That'sfor reading guys!