emily:

I am in a similar situation... i am being forced (practically) to use clear
finger nail polish instead of a pva ( i think that's correct??) solution.
ugh!  but i am doing the best i can.  I have used both pigma pens in the past
as well as ink and quill....  i don't recommend using the white out though!

What I was taught to do was to put a clear layer down first... let it dry ...
then the number... then another clear layer.  supposedly it is reversible that
way.

i also know that you must be careful w/ acetone.. i have worked with several
ppl who have been in the museum business for quite some time and feel that
they have health probs. related to handling acetone carelessly (as compared to
todays standards).

I'm sorry if I have not really given any answers.. it's very late right now
and perhaps when i have had some sleep I could actually look some of the stuff
up!  :)  but I hope this helps nonetheless ... good luck!

Sincerely,
  Ginger M. Young