What do the Sizes of Linen Thread Actually Mean? It’s Complicated.

Some common sizes of linen thread for bookbinding, ranging from 18/6 to 80/3.

Bookbinders likely know that linen thread is classified by a two number system, such as 35/3. And most know that the second number represents the number of threads plied together, and the first number how thick or thin the thread is.  But what does the first number actually refer to?

It turns out that two different systems, an English system and a Metric system that use a similar two part description of size separated by a forward slash. However, these two systems are not the same. Most thread sold by bookbinding supply companies uses the English System.

The English system (aka. Number English, Lea, NeL, Linen Count) is based on how many skeins (of 300 yards) make up one pound in weight. I *think* this means that twelve  12/1 skeins would weigh one pound, or thirty-five 35/1 skeins would weigh one pound. I’m still not sure how adding the plied threads results in the classification. Would a 35/3 thread weigh 3 pounds?

The Metric system (Nm, aka. the Japanese Gunze Count) is based on how many meters of thread weigh one gram.  So I think for a 60/1 thread, 60 meters weighs one gram. It is the same as the English system in that overall, thicker and stronger threads have lower numbers.

Other thread systems include:

Tex — How many grams 1,000 meters of a thread weighs. In this case, the larger the number, the thicker the thread.

Denier — How many grams 9,000 meters of a various thread weights. Again, the larger the number, the thicker the thread. This is useful for very thin threads and microfibers.

Grist — Yards per pound.  For example, a 20/1 linen is 3,000 yards long per pound. Different fibers have different weights.

I’m still not sure what system the Londonderry Linen Lacing Thread in the image above uses. It is labeled only a mysterious “#4”. I love sewing with this thread, though, since it is thick, soft, easy to untwist, tangle free without waxing, and remarkably compressible. It is possible to sew a book naturally packed with it. It consists of five plies, and is roughly equivalent to a 20/5.

If you are wondering what size thread you should use to sew a book, check out my Guide to Swell.

Finally, Colophon Book Arts is a reasonably priced, one stop shop to purchase a wide variety of sewing threads.

Wait, there are more systems  … AARGH!      https://en.wikipedia.org/wiki/Units_of_textile_measurement



Cor Knops, of Knops Boekrestauratie in the Netherlands,  kindly sent me these images of some antique thread he owns.


Great name!

These packages contain hanks of thread, and all weight about a pound.  I think the package on the left is 25/3, and on the right 12/3. So if my calculations are correct, the 12/3 should contain 1200 yards of thread, assuming a 12/1 would contain 12 – 300 yard skeins = 3600 yards.  Enough thread for a lot of books in any case!

Don’t Wash … Scour!

Last summer I recorded my investigations into replicating early 19th century book cloth  using XSL pigments. One difficulty was achieving an even coloring, and several commenters indicated I should scour the fabric, rather than just wash it. Finally, I had a little time to try this, and although I haven’t had a chance to do more dying, tests with wheat starch paste have been astounding.

Note all the yellowish junk that came out of the muslin: oils, waxes, and pectic substances.

I boiled 1.5 yards of Springs Creative 45″ unbleached muslin (133 x 72 thread count, .007″ thick, $4.00 a yard) for two hours in a stainless steel pot, using 1 tablespoon of soda ash per 6 cups of water. Since it smells a bit, it is advisable to have a externally vented exhaust hood.  A long stirring stick is necessary, as are rubber gloves.

Keep a close eye on the boiling muslin. I used large pieces of cloth, for future use as covering material. As the water boils, hot areas form bubbles under folded and wrinkled areas. Then when you stir, they get released and the pot bubbles over, or worse, spills on you. I stirred the pot every 15 minutes so that all cloth surfaces were exposed to the scouring, and adjusted the temperature as necessary to keep an even boil.

The scouring raised the pH of the cloth from around 5 to 7, though this was measured with testing strips and is likely not super accurate. Soda ash is around 10 or 11 pH. The scouring removed oils, waxes, and pectic substances. The cotton fibers swelled and softened during the process.

Muslin samples pasted onto Mohawk Superfine. Left: Scoured. Middle: Washed. Right: Untreated. Note the superior adhesion of the scoured sample, skinning the paper during a pull test.

The difference in adhesion between the scoured, washed, and untreated samples is remarkable. All were pasted with Aytex P wheat starch paste onto a piece of Mohawk Superfine, with the same weight during drying.  I testing the adhesive strength by pulling the fabric away from the paper at 180 degrees. The scoured sample delaminated the paper, while the washed sample (hot water, a tiny bit of Seventh Generation Free and Clear detergent, industrial washing machine) and untreated sample released without affecting the surface of the paper. I tried this two more times, and the results were the same. In a separate test using EVA all the samples delaminated the paper.  I’d like to get a push-pull gauge to quantify the adhesion a bit more rigorously. Of course, there may be circumstances where a weaker adhesion is desirable.

But for most book conservation applications — spine linings, board slotting flanges, hinges, sewn stuck-on endbands, covering material — strong adhesion is desirable.


The New Glue Pot from Lee Valley is Excellent. Gelatin and Paste for Lining Spines

Lee Valley Glue Pot

Lee Valley, perhaps the most innovative large woodworking tool company, recently introduced a one ounce cast stainless steel double boiler glue pot, which is perfectly sized for book conservators.

It works great with gelatin in conservation work or with hide glues for historic models. The heavy cast steel double boiler gives a very gentle and even heat.  It is based on a Landers, Frary & Clark glue pot from the 1870’s. There is an image of the original, which was cast iron, in Stephen Shepherd’s hide glue book. (1)

The cup-warmer is cheaply made, but it only costs a dollar when purchased with the gluepot. If the interior of the pot was finished a little smoother to make cleaning easier, it would be perfect. A steal at $35.00.

Arthur Green described his investigations using gelatin on the spines of books in the blog post, “Revisiting Animal Glue: Gluing-up with Gelatin” Traditionally bound books used animal glue on the spines, and paste for the covering and paste-downs: there must have been a reason. He tested starch paste and gelatin separately, and primarily for adhesion.

I find the real magic happens when gelatin and paste are used in sequential layers, or mixed together. Dudin, in the 18th century, described the “marriage” that happens between animal glue and paste. (2) A mix gives the book better resistance to torquing than paste alone, makes it feel more solid, and gives a more secure — yet still easily reversible — bond with a Japanese tissue for the first spine lining in conservation work.


  1. Stephen A. Shepherd. Hide Glue: Historical and Practical Applications (Salt Lake CIty: Full Chisel, 2009)
  2. R.M. Dudin. The Art of the Bookbinder and Gilder, Trans. by Richard Macintyre Atkinson (Leeds: The Elmete Press, 1977)