Penwork was my nemesis for a long time, and it can be a long and tedious process as it’s slow work. There is a cheats way of doing this. I wouldn’t recommend it for precise and detailed work like zentangles but it’s great for faint outlines and saves quite a bit of time. Draw or copy the design onto tracing paper, then trace onto cleaned porcelain using waxy carbon paper.
Then using powder enamel lightly dust over the design, wear a dust mask and don’t inhale the pigment. Move it over the design with a soft dry brush.
Here I used a lighter grey for the distant buildings andblack in the foreground.
Then dust off the excess with the brush and clean up with a cotton bud if necessary.