A few months ago I posted a query "What have we learned in preservation
techniques since the 1960's".  I didn't get much - no one even said they had
figured out that roofing tar was not a good preservation material.

Let me try another way:  In the field of preservation, what kinds of things
do we still not know?  What do you hope we will know in another 10 or 20
years?

Christopher Gray
(Hopes we will finally figure out possible height of ivy growth.)