@Sunfish...
Vet Don Angwin's son has it in Perth. "Fablon" is the name of the transparent plastic you are thinking of....and by the time of my visit to Perth back in 1994, to my surprise, the map had been covered in it. People do have the idea of carbon dating the writing by (what looks to me as) indelible pencil but on enquiry about carbon dating they cannot be as exact as to a "year" only to like 50 years or so. Indelible pencils stopped being used in the late 40's to early 50's because of lead poisoning.
Last edited by David Billings; 2nd Jun 2018 at 05:06.