I know that in some parts of the world like medieval europe, marking of the body was considering sinful, however regardless of that, how long would the process have taken for one that would want one?
I know these days that tattoo artists have various sessions, however, I'm looking more so for the medieval perspective and time frame, given that I'm writing a story which involves each person of a particular military group, bearing the same symbol on their back or arm.
Also, keep in mind said symbol would either be the length of the arm and/or back and would only be black, with no colour. If you know the type of dye they would use and what tools they used as well, that helps too.
If I can tack on a follow up question:
Do we have records/examples of the specific tools used?
Or records of specific tattoos to be found in Europe from the period OP has in mind?
I'd be curious to see if/how a European tattooing process would compare to the traditional methods in my neck of the woods.