I'm not very sure about the vinegar + steal wool part... that makes ferrous acetate pretty quickly, and what we want here is a ferro-gallate. I think there are ways of producing ferro-gallate inks without using sulfates, but historically ferrous sulfate was commonly used ( and leads to paper being eaten away over time )
Excellent comment. I'm one of those people who always thought: "I can't draw". Now I understand that for me it is a matter of practice. I started with Drawing on the Right Side of the Brain.
This book is not really addressing the more common "is math real" question of it being empirical or invented. For an interesting take on that question, see the 1st section of the 2nd part of Daniel Shanks' Solved and Unsolved Problems in Number Theory. He makes some interesting points about the old Pythagorean views