As a registrarial assistant at a small county historical society (read SLAVE
LABOR) it was impressed upon me that whiteout was bad for artifacts.  We used
a base coat of B72 in toluene, wrote catalog numbers in black or white water
soluable ink, and put another coat of B72 over the ink.  This was considered
acceptable because the numbers could then be removed with acetone.  I don't
now the chemical composition of B72 or toluene but it seemed to work great
for us.  (A heck of a lot better than the method used in 1977 at our museum;
namely, masking tape & ballpoint pen - yowtch.)
 
Of course, painted wood and metal surfaces suffered a bit from the acetone.
 
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