A Guide to Swell

In bookbinding, the term “swell” describes the thicker area of a book block at the spine due to the addition of sewing thread. It depends on factors detailed below, but a binder or conservator generally does not have control over all these variables. Knowing how to estimate the amount of swell that will develop is one of the most important aspects when planning to sew a book, since it corrolates to the degree of round and the shape of the shoulders that a book will end up with.

Different binding styles need different amounts of swell. Too much swell creates a textblock that is unstable, squiggly, and difficult to back. Too little swell and there are insufficent shoulders which are necessary for some styles of binding. In all case binding structures, there is more leeway with amount of swell, and as long as it is not excessive it will be sucessful; with bound books the tolerances are much tighter. For example, if you are resewing an existing text block it is critical the new shoulders exactly fit the original boards.

Softer, multi-ply threads afford much more control of swell while sewing as compared to a hard modern thread. Currently, I primarily use threads sold by Colophon Book Arts, including the Colophon Best Blake Thread and the Londonderry Linen Lacing Cord #4. Both can be deplyed if desired to make them thinner. I also prefer to support smaller, specialist bookbinding supply companies. If you are using standard threads, 25/3  is a reasonable starting place. 

Many early binding structures—even up to the late 18th century—manipulate the shape of the boards to fit the spine, rather than the modern fine binding tendency to fit the boards to a 90 degree shoulder.  This makes it easier to fit a wider range of boards to a given swell. Obviously, this is not an option for many binding structures.

There is no formula, instead these ten aspects need to be considered:

1. THICKNESS OF THREAD. Thick thread (or more plys) = more swell. Thin thread (or fewer plys) = less swell. Although not ideal, the thickness of thread can be changed during sewing if too much or too little swell develops. 

2. HOW HARD OR SOFT THE THREAD IS. Hard thread does not flatten in the signatures = more swell. Soft thread flattens in the signatures = less swell. A compressible thread gives more control. It is often advisable to untwist hard modern threads a bit to make them softer by running them through your fingernail and thumb, and let them relax.  Waxing thread also makes it harder, so I generally avoid it if possible. Sometimes excessive kinking and twisting comes from using too small of a needle. Softer thread can fray more during sewing, though. 

3. THICKNESS OF THE TEXT PAPER. Thick paper absorbs more thread = less swell. Thin paper absorbs less thread = more swell.

4. HOW HARD OF SOFT THE PAPER IS. Soft paper absorbs more of the thread = less swell. Hard paper absorbs less thread = more swell. It is easier to control swell with softer paper. Guarding the spine will increase swell. Washing and resizing can also affect how much swell develops. Swell can also be adjusted before sewing by beating or otherwise compressing the sections.

5. HOW MANY LEAVES ARE IN EACH SIGNATURE. More leaves can absorb more thread = less swell. Fewer leaves = more swell.

6. HOW MANY SIGNATURES THERE ARE. More signatures = more swell. Fewer signatures = less swell. Some binders like to visualize this by wrapping the thread around a pencil the same number of times as there are signatures.

7. SEWING STYLE. All-along, two-on, three-on, etc. All-along produces the most swell, more “-on” sewing styles = less swell. Packed sewing produces more swell due to a small overlap of thread. This can be controlled, to produce naturally packed sewing, which has one length of thread on the cords for each signature.

8. SEWING SUPPORTS. Tapes, cords, thongs. Tapes produce the least swell, cords and thongs slightly more since the thread can overlap slightly inside the signature. Supports also differ in the amount of adjustment that can be done after sewing, ie. how much the thread can move on the supports during consolidation and backing. A professional sewing frame, such as the Nokey makes this easier.

9. HOW MUCH CONSOLIDATION IS PERFORMED DURING SEWING. More consolidation during sewing= less swell. I have often observed students sewing identical text blocks, with identical thread, end up with significantly different results. A loaded stick, or knocking down stick can help with compression, although some people prefer to use a bone folder or wedge shaped piece of wood.

10. TIGHTNESS OF SEWING. Tighter sewing makes a thinner book before pressing. Looser sewing can develop due to improper tensioning or too large of a needle. A book sewn too tightly can develop a “banana” shape, thinner at the kettle stitch. Even tension is crucial.

Best practice: sew with the thickest thread possible.

News from 1886: Hand Bookbinding is Slowly Disappearing

“Bookbinding on a small scale seems to be one of those minor industries which are slowly disappearing. Yet we think that there is always a certain need of a good bookbinder in every country town. We recollect how such a person was once maintained in a small European city by official work, and now and then a few orders from the country gentlemen. Shopkeepers and farmers as a general rule are not bibliophilists. When, however, we come in this country to look upon a book as something of intrinsic value, we will insist on real books, in proper shape and goodly binding, and then the bookbinder’s day will have come.”

The Bookmaker: A Journal of Technical Art and Information, January 1886, p. 16.


Uses for a Delrin Hera

Image courtesy Joan Weir

Image courtesy Joan Weir. This delrin hera is .25 inches wide and 6.5 inches long.

“My new favorite tool. Every paper conservator should have one in their tool kit. Fabulous for control on soft of thin supports, makes adhesive and hinge removal a breeze. Beats Teflon by far.”   – Joan Weir, Paper Conservator, Art Gallery Ontario, Toronto, Canada.

I also find myself using this tool more and more.  Some other uses:

  • Manipulating fragile pages or tissue
  • Delaminating boards or covering material
  • Keeping lifted areas open during rebacking or board attachment
  • Lightly scoring tissue in complex shapes for paper repairs
  • Applying controlled pressure during paint consolidation or tissue repairs
  • Inserting adhesive into delaminating areas
  • Delicate scraping. Better edge retention than teflon and softer than steel on paper
  • Tape removal. Can be heated to 180 degrees Fahrenheit and resistant to most solvents
  • Holding things during photography. Less reflective than steel and looks cleaner

Only $40   How to purchase and more info 



The Mother of all Insect Galleries

“M. Pignut mentions an instance where, in a public library but little frequented, twenty-seven folio volumes were perforated in a straight line by the same insect [a bookworm], in such a manner that, on passing a cord through the perfectly round hole made by it, these twenty-seven volumes could be raised at once.”

-John Andrews Arnet [John Hannett] Bibliopegia, or, the Art of Bookbinding, in all its Branches (London: Richard Groombridge, 1835), 201.

Hot Violet OptiSIGHT Magnifier


One of the few benefits of aging eyes is that you get to wear fancy headset magnifiers while working, like Donegan’s OptiSIGHT in violet!

Weights of Litho Stones


G. Ruse and C. Straker. Printing and its Accessories. London: S. Straker & Son., 1860. Robertson Davies Library, Massey College. University of Toronto.

This is a pretty handy chart if you are considering purchasing a litho stone, or even picking one up to move around.  For example, a 16 x 12 inch stone weights 43 pounds per inch of thickness. This was pasted onto the inner face of the front board of Printing and its Accessories from Massy College.  Another reminder that many printed books contain unique, owner added paratextual information.

Tool Demonstration, Roundtable Discussion, and Pot-luck Meal. CBBAG Bindery, Toronto.

Monday, October 26, 2015  6-8pm.

CBBAG Bindery, Suite 207, 80 Ward St., Toronto

This is a free event open to the public, but you must RSVP:  cabbage.gta AT gmail DOT com


I will demonstrate the making of a delrin folder using simple hand tools: a hacksaw, a file, a scraper, and micron-graded sanding sponges.  Attendees should bring their favorite tool and be prepared to discuss it. Also bring a tool that doesn’t work or you would like to alter, we can brain storm options as a group. The evening will conclude with a pot luck meal, I’ve already heard rumors of chili. Yum!