[mikhailfranco]

A sketch of twistor space:

https://theportal.wiki/images/1/11/Penrose-Rindler-Clifford-...

A Penrose slide pack:

http://cgpg.gravity.psu.edu/online/Html/Seminars/Fall1998/Pe...

For example, slide 19:

http://cgpg.gravity.psu.edu/online/Html/Seminars/Fall1998/Pe...

An original manuscript with fully formed illustrations:

https://math.ucr.edu/home/baez/penrose/Penrose-TheoryOfQuant...