On Fri, 18 Dec 2015 23:28:59 +0000 (UTC), Cydrome Leader
wrote:

What the color of highlighter that would copy solid black even though you
could still read the original?

I don't know and too lazy to test it on my copier.

Interesting stuff:
http://www.protectedpaper.com/category_s/17.htm

The copiers here are just color scanner/printers so they don't have the
same spectral sensitivity as the old machines so I can't test.

I have an (old) Canon PC785 mono copier which should work. However, I
don't have any highlighters to try.

Incidentally, I use a special ink for the purpose, that fades to
invisibility in about a year. It helps keep the manuals nice and
clean.

They should make heated pens for writing on thermal paper.

Ummm... They do. It's called a soldering iron. However, there's a
trick to using a soldering iron for writing. Be sure to grab the
correct end of the soldering iron. The rest is self evident and easy.

Too hot and the thermal paper cycles back to white. It does weird things
when heated to the transition temp range.

Too hot and the paper catches fire. As I recall, the paper was black
or brown before it started burning. I just tried it with some thermal
receipt printer paper. It didn't go back to white.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558