What size tattoo needle is use for a portrait?

You will want to set up no less than 3 machines for a portrait, but 4 would be better. You will set up a liner with a 3RL needle, and this will be used VERY little. The downfall to many portraits is the use of too many hard lines, thereby making it look like a cartoon and not a photograph. You will use this liner for details such as eyelashes, hair strands, pores, etc. Next, you will set up a shader with fairly long stroke with an 18RS and this will be used for the majority of the smaller areas of shading and you'll do a lot of your sculpting with it. Next, set up a shader with long stroke with around a 15CM - 25CM, and you will use this for the majority of the large areas of fill and I find that they work well for backgrounds as well. In addition to this set up, I often use a liner with a 7RL for highlights and other small things.

When doing black and gray portraits, you build from dark to light, and with color you build from light, to dark, and then back into light. Always remember to have a background to contrast the subject which should be lighter and a bit blurrier than the subject of the piece, thereby making the contrast all the more significant and adds to the three dimensional quality to the piece. And always, always, ALWAYS remeber your light source. This can literally make or break a good portrait.