Let’s get the obvious one out of the way first. My preferred way to draw lines in watercolour is to trace the line lightly with a pencil and a ruler (or the side of a pencil or a brush handle if I don’t have any ruler), then to paint the line free-hand.
I steady my hand by touching the paper with my little finger. I could use a ruling pen, but I find the result too mechanical.
Lines with masking tape
Stick the masking tape where you want the line, paint the line along the masking tape and then remove the tape. It is quick but does not give the best results on rough paper.
This method seems easy because with the masking tape you don’t need to worry about painting a thin line. However, it is not easy to get a regular line because you can’t really see what part of the line goes on the masking tape and what part goes on the watercolour paper.
A word of caution: try sticking the masking tape and removing it on the back of the watercolour paper first to make sure it does not rip-out the surface of the paper.
I tried a simple printing technique: I painted the side of a mount card with paint and use it to print blue lines by pressing it on the paper.
The line on the right is the first one, I then printed several times on the left of the first line without reloading with edge of the card with paint.
The result is more random than with the other techniques, as the quality of the impression depends on giving the paint the right consistence. The watercolour paint dries quickly and it is difficult to control the final result. In addition, the paint is not going in the dips of the rough paper.
Next time, I will look at another interesting technique to draw lines in watercolour.