De-yellowing by the sun only.

It largely worked! I've written an article showing the results here:
https://www.classic-computers.org.nz/bl ... n-only.htm
https://www.classic-computers.org.nz/bl ... n-only.htm
Connecting New Zealand's vintage and classic computer enthusiasts
https://www.classic-computers.org.nz/forums/
https://www.classic-computers.org.nz/forums/viewtopic.php?f=11&t=2420