which is also the subject of most of the pictures and texts in the book

They are available in three different sizes

The top wire-O twin ring binding opens completely flat and folds back on itself for a rigid self-supporting workspace

though still transparent like all other watercolors

tombow airpress pen black 0 7mm Money which is also the subjectThe Tombow AirPress writes the way most pens can't upside down, straight overhead, on damp paper, or down to 5C because of an internal pneumatic piston rather than relying on gravity to feed ink toward the tip. Every click of the button compresses air inside the chamber, pushing the oil based ink forward under pressure instead of letting it pool or stop flowing whenever the pen tilts or the temperature drops. That makes it a genuinely different tool