I did a sketch with micron pen while traveling in Beijing many years ago. I quite like the result, but also wondered what it would look like with some color. I didn’t want to paint over the drawing, fearing that I might ruin it. So this was the solution I came up with:
I first made a photocopy of the drawing.
Then I transferred it onto a canvas (‘Glue’ the photocopy onto the canvas with acrylic medium and scrubbed off the paper when it’s dry. The image will stay.)
Next I glazed over the image with watercolor. The surface was not comparable to regular watercolor paper, so I only did a few layers of light washes.
When it’s bone dry, I varnished it with acrylic medium (gloss). I didn’t know there were spray-on varnishes back then, so I brushed on the medium, It did disturb the paint a bit, but since it’s very dry and very light layers, it’s not that bad.
Since it’s varnished, I could hang it without glass. And I still have my original sketch! 🙂