You don't have, Brian, just a challenge against yourself !
If I remember:
1) have layer underneath thoroughly dried several days or a week.
2) draw the drawing first on paper and try on paper at scale
3) keep a clean brush and some white spirit and an absorbing pper ready
4) sketch the shape with the paint diluted first, so very light tone,
5) if mistake, remove immediately with brush; if dried, dip point in WS, remove liquid on paper towel and 'erase' paint immediately
6) let dry 2 minutes to let WSdry out before resuming paintingto prevent spreading of your trace.
7) when drawing is good start darkening slowly the motive
adjust for shadows and highlignting on the arm..
I will have to do also in two weeks, we can discuss our mutual expérience together (my arm surface is 5x12mm) for a celtic tatoo.
