‘ Mornin’ Ed
I agree with all that you say.  I never have any issue with shellac.  I should
have been more exact in my comment.

 “Before you start, you will have considered the chemistry of all the products
you may be using, and you will be conscious that if you seal timber with shellac
- lets say you need to control end grain absorption of colour - then cleaning it
out will be almost impossible.
But then - why would you need to?  Shellac is happy with almost everything else
you may want to put on top of it.  I’ve never had to investigate the most modern
’stuff’ but if you were to want somehting like, I don’t know - a 2 part epoxy
coating - it might want to be on the timber rather than have an intermediate
layer.  The get out of jail card is to say  “test your intended process os an
offcut’  that way, if what I say is complete rubbish, and responsible for you
losing a thousand hours of work - it isn’t my fault! “

I do have some old product - as old as me or more, whose chemistry is a bit
uncerain to me.  Don’t mix with spirit (alcohol) or water,  therefore I’m always
wary.   Stay with shellac ground to allow water based colour colour control, and
go to top coats of shellac or oil varnish/shellac mixtures for the final finish.
Never fails..




Richard
Still in the Borders (bit of country separating Scotland from England, Paddy)