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Re: Fan-gluing

>Date:    Tue, 24 Nov 1998 07:21:23 -0800
>From:    Betty Storz <storz@xxxxxxx>
>Subject: Re: Fan-gluing

>>What kind of mull do you use?...  Several months ago, there was an =
thread about double-fan gluing on the List and someone recommended a
stretchable mull, with the advantage that there would be a little give
along with the elastic adhesive lessening the tendency for the text block
to pull away. <<

   I use the cotton specification backlining sold by LBS.  This is the =
non-stretching backlining material they sell.   In my highly opinionated =
view (might as well be honest) a stretch super can only be justified when =
the textblock is going to be rounded and backed after it is glued-up.  The =
rounding and backing operation essentially enlarges the area of the =
glued-up spine.  A non-stretching super will either  separate at various =
stress points or resist the rounding operation completely.   As I see no =
justification for rounding and backing an adhesive binding I see no reason =
for a stretch super. =20

   The super is the  first structural layer next to the glue line.  It =
should be flexible but non-elastic.  The flexibility allows the super to =
move with the spine as the book opens.  The non-elasticity adds control to =
the forces that tend to spread the glue line and stress the bonds between =
the pages when a book is opened.   Both stretch and non-stretch supers =
offer plenty of flexibility.  A "stretch"  super, however, may potentially =
spread and distort the glue line.  The possibility of this happening is =
probably fairly remote if the super is the only lining on the spine.  If =
anything is added on top of the stretch super, such as kraft paper lining, =
the probability of this distortion increases significantly.  I should also =
note that the term "stretch" in regard to the LBS super is probably a =
misnomer.  The term "stretch" indicates elasticity, the ability to deform =
from a certain shape and to reform to that same shape when stress is =
removed.  The "stretch" supers I have seen would be better called =
"expanding supers" as they will stretch out to a new, larger shape but =
will not contract to the original shape once the  stress is removed.  This =
expanding and non-contracting characteristic is exactly what rounding and =
backing requires and is, I believe, probably the sole reason why stretch =
supers were created.  =20

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