In article ,
John wrote:
Materials technology has changed a great deal in the past few decades, so I
am hoping (L-A-Z-Y) that there might be a flexible, nonsticky, spray-on
coating that can be applied inside and outside a large bellows (for 10X10"
enlarger).

Spray-on, no. But Permatex Ultra Black gasket maker (available at your
local auto parts store) works well, though it does not leave
a smooth interior surface. It is rubbery, not sticky, once it dries.

I use a small piece of black gaffer's tape on the outside to make a backing,
then Ultra Black on the inside. Remove the tape backing, or not, after the
gasket maker dries, according to your preference.

--
Thor Lancelot Simon

"The inconsistency is startling, though admittedly, if consistency is to
be abandoned or transcended, there is no problem." - Noam Chomsky