Hi John,
There is a thin tape in different thicknesses for lines - just google fine line tape.
You might also want to look into frisket film. It's used for masking airbrush designs. I use it for things like those Mondrian style platters and the multi-colour sunburst designs etc. You stick it on over the whole surface, mark out your design and cut with a scalpel the peel off the areas you want to spray. It can be stuck back again if you're careful so you can mask areas already sprayed.