Homebrew PCBs

Not sure if the dating on this make a difference......
I bought HEWLETT PACKARD
Disposable Liquid-Ink drafting Pens
.5mm Medium Point   HP Part no 5061-7620

says For use on paper or vellum only on the package

and drew on copper .5 mm traces.

The ink looked very wet so I did two passes and let it dry on a heater vent.

Then.... etched in peroxide and muriatic acid.

All the black traces looked intact until the very last etching copper 
disappeared
BUT
one swipe with a light touch makeup brush simple wiped away the black 
traces to reveal ZERO
copper under the ink traces.

The package said USE BEFORE JAN 1992 so perhaps I would get a different 
result from
TODAYs inks instead of using 25 year old ink. Who knows if they even use 
the same chemistry now.
But for paper.... these are really nice pens.