Observations on Blade Angles of English Style Leather Paring Knives

“One of the most admired skills in bookbinding is the paring of leather, yet only sharp tools and confidence are required.  Confidence is gained by experience, and sharp tools by a zelous consideration and care for knives.” Arthur Johnson, The Thames and Hudson Manuel of Bookbinding, p. 89

I would add that it is also critical to pay attention to the blade angle of the knife, since it affects how the knife cuts, the angle one holds the knife at, and consequently how the leather is cut.  I’ve found that roughly a 40-50 degree angle works best for edge paring.  First, a few terms defined.  The blade angle is from an imaginary line 90 degrees to the length of the blade.  I am calling a zero degree angle one that would be straight across where the dotted line is, pictured below would be roughly a 45 degree blade angle.  The bevel angle is the amount of slope on the bevel, in the case of leather paring knives usually around 13 degrees.  The diagram below is the style of knife a right handed binder would normally use. (1)

 

I’ve found there are two main issues that determine the optimal angle of the blade– how much the blade is skewed in use and how the knife is held.  The way I hold and use an English paring style knife is outlined below, as are the reasons why I consider a 40-50 degree blade angle ideal.  

Skewing the blade in use reduces the effective cutting angle, improving the initial cutting performance and not altering edge retention.  Although the more acute the bevel angle is the sharper the blade will be, if it is too severe the cutting edge will be very fragile and quickly deteriorate.  I haven’t figured out the math, but if the bevel angle is 13 degrees, I estimate an extreme skew reduces the effective cutting angle by a degree or two, which is significant.  

I tend to use an English style paring knife in three ways when I am edge paring- first to make a series of cuts using moderate skew, then a few finishing cuts using extreme skew, and finally use the knife with no skew, almost like a spokeshave, to smooth everything out. It doesn’t seem to make too much difference if you pare across the skin, as pictured above, or push the knife away from you.

To make a long, even bevel the angle of the knife held steady by my thumb and second finger on the other side of the the knife– they slide along the surface of the paring surface. In order to pare the leather evenly, the knife must be held at a consistent angle. (2) The angle the knife is held varies with the type of leather and skill of the binder- too high of an angle takes off virtually no leather, makes it more likely to slice through the flesh side of the skin and dulls the knife tip by digging into the paring surface.  Too low an angle makes the knife difficult to control, since most of the cutting edge is engaged into the leather.  Wide knives with long bevels exaggerate this problem.  Right handed beginning parers may want to use the forefinger of left hand to push the knife along the leather.  This allows one to concentrate on using the right hand to hold the knife at a consistent angle, as illustrated below.

One reason I dislike jigs for sharpening is that the hand skills to sharpen the knife are remarkable similar to the hand skills necessary to operate the knife– if you don’t have the hand skills to hold the knife at a consistant angle to sharpen it, you are not going to be able to hold it at a consistant angle to pare leather evenly.   Some like to pare across the leather, as illustrated below, and some like to pare up the side of the leather, starting the cut with the heel of the knife rather than the tip. Since lithographic stones are now extinct, I prefer paring on a piece of glass and saving stones for printers wishing to experience printing on a real stone.  There is no reason to pare on a litho stone other than tradition, and I suspect the only reason they were historically used is that they were a cheaper flat surface than glass, marble or granite

 

 

 

 

 

 

 

 

 

 

 

 

After a first cut is made, a second (and possibly third or fourth, depending on how long of a bevel is desired) is made by holding the knife at progressively  lower angles.  The depth of the cut can be judged by changes in the color of the leather or folding the leather in half, which doubles any errors.    If the leather is disturbed to check the progress, it is imperative that any stray bits be cleaned from under the skin, otherwise the knife will cut through these thicker layers.

As the leather becomes thinner, it becomes weaker, so I adopt the second knife position.  I skew the knife towards a more extreme angle and press down harder, which creates a lower effective bevel angle. This helps prevent tearing the leather.  It is much easier to take the leather off in long even strips with the first cuts, rather than try to correct mistakes later on.  If there are many irregularities, sometimes it is easier to use a spokeshave to even things out.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

After the edge is pared to the length and thinness desired, I rotate the knife into the third position, so that it is not skewed, and push it forward to even the previous cuts out.  This is almost more of a scraping action than a paring cut, and is meant to smooth out irregularities left from the previous cuts, not remove a lot of skin. The angle of the camera in the illustration seems to exaggerate angle that the knife is being held- in reality it is almost parallel to the skin. Again, a spokeshave could do this as well. The cutting edge of this knife is one inch, which is slightly larger than most turnins. Most of the time 7/8″ is a reasonable turn in width–compromising between giving a little extra room in case the leather is torn, and conserving leather.  One unintentional consequence of the acidic nature of some leathers is that they rapidly stain the pastedown, making it possible to observe in detail the pattern of trimming and size of turnins.  I admire the judgement (and frugality!) of some binders, capable of covering the book so economically that only a millimeter of two of leather extends under the pastedown in various places.

 

 

 

 

 

 

 

 

 

 

 

 

 

A roughly 45 degree angle seems to be the most comfortable in all three of the ways I hold the knife.  I have a set of knives that I use when teaching which consist of 22.5, 45, and 67.5 degrees, in order to compare what is most comfortable for each individual, and most opt for a roughly 45 degree angle. Another consideration is the angle of the wrist when using the knife– I’ve found around 40-50 to be most comfortable.  Keeping the angle of your wrist comfortable is important if you do a lot of production work, to avoid carpel tunnel syndrome.  Any numbness or tingling sensation is possibly a very serious problem, and medical attention should be sought.  Choosing a good quality knife, keeping it well stropped and sharp will also reduce the force needed to pare leather, reducing strain on the hand and wrist.  Finally, a 45 degree blade angle is much easier to sharpen than a 67.5 degree angle for two reasons– it is easier to get even pressure across the entire width of the bevel (especially the tip), and there is less metal to remove, so the sharpening is more rapid.  Paring leather is not difficult, as Johnson pointed out, it just takes some practice with a sharp knife, and an awareness of the blade angle.

 

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NOTES

1. As a left handed binder pointed out to me, simply changing the direction of paring allows a right hander to use a left handed knife, or vice versa.  Below I am comfortably using a left handed knife, holding the leather at the top and paring towards myself.  

 

2.  Some find it more comfortable to hold a knife with a handle.  In this case, it is sometimes necessary to hold the handle area of the knife off the paring surface in order to achieve a low angle.  This illustration also demonstrates side to side paring.

French Leather: 1755 vs. 1810

Godfrey Smith’s The Laboratory or School of Arts is an important, and popular 18th  C.  description of bookbinding.  It was published in at least 7 editions over some 70 years.  Reproduced below are two paragraphs, dealing with “French leather”, which is a method of sprinkling leather. It is extremely prevalent during that time period, and Dudin mentions that “…our eyes are so used to seeing it there that the work would seem unfinished if it was absent.  Moreover, it is, to a certain extent, necessary to hide the minor defects…in calfskin.” (Dudin, 52)  He later notes that it is too expensive to use Natural Calf, since one would have to use leather without holes in it.  Patching holes in a leather binding– almost unthinkable today, given the reversal in the price of labor vs. materials– was considered standard practice. In this time period a pencil means a brush.  Note that hog bristles have yet to be replaced by a synthetic for bookbinding brushes.  This was an English book, commenting on a French tradition, and it appears the author colors the leather (“strain it on a frame;”) before covering, although the French generally applied color after covering.

But what I find most interesting, about the two passages reproduced below, one from the fourth edition, 1755, and one from the seventh, 1810, is how much closer to our own times the 1810 edition is.  Even apart from the long ‘s’, the whole look of it is different in ways that relate to the change in binding structure at this time–from a bound book to a cased one, which I have discussed in another post.  Still, there are some interesting similarities, such as the eccentric italicization in the title.

Although the text is virtually unchanged, the change in typography and the standardization of the printing is dramatic. The letter spacing is more open, even and controlled in the seventh edition contrasted to the fourth.  Visually, all the lines are much more even in the seventh, making the fourth look crude or charming, depending on your viewpoint. Just looking at the differences in these examples highlights the tremendous influence of the beginning of the industrial revolution, and the radical changes that occurred in book structure, machinery, tools, typography and in the world.

Fig. 1The Laboratory or School of Arts. Fourth edition, 1755.

Fig. 2.  The Laboratory or School of Arts. Seventh edition, 1810.

Dudin, M. 1977. The Art of the Bookbinder and Gilder. Trans. R. Atkinson.  Leeds, England:The Elmente Press.

Thoughts About Board Shears

Depictions of standing and lying presses tend to be very popular logos for bookbinders and conservators, but an image of a  board shear might more accurately symbolize current hand bookbinding practice.  More than any other tool or machine in a bindery, the board shear demarcates the difference between in-boards binding and case binding, it highlights the difference between the late 18th and early 19th centuries binding styles, it marks a major shift in the role of bookbinders from artisan to worker, and often today it reflects difference between an amateur and professional binder.

A board shear does one thing, it cuts a piece of cloth, board or paper at 90 degrees quickly and accurately. Physically, the board shear is often  the largest machine in a hand bindery. My relatively small 19th C. 30″ Jacques takes up about 20 square feet. It quite heavy and expensive as well.  For these reasons most amateur binders do not have one. It’s imposing presence, however, garners many comments from clients.  Although the large blades appear dangerous, most accidents I’ve witnessed involve pinching one’s finger under the fence, then jumping away from the machine, and in the process stepping down harder with the foot clamp, which squeezes one’s finger even more.  A torn off fingernail is often the result.  And I have seen the counterweight fall off the end, which could have been deadly.

The earliest publishers case bindings appear around 1810, and the board shear around 1840.  There are types of earlier case bindings, wrappers and related structures, but I am just considering publishers case bindings here. It is difficult to imagine a 19th C. publishers bindery without one, since it is made for dealing with the relatively new invention of book cloth and machine made binders board. Machine made binders board, with an even thickness, is perfect for cutting on the board shear.  Earlier water leaf or paste board usually vary considerably in thickness (possibly explaining the remarkable amount of beating prescribed in historic bookbinding manuels) and make it a poor canidate for use in a board shear- the fence must hold the material being cut evenly and firmly, otherwise it will tear rather than cut.  With a bound book, a plough is the most necessary piece of specialized equipment, not the board shear.  

19th C. case binding, consisting of two boards, a spine piece and covered before gluing to the text block, requires much more accurate, repeatable cutting that a bound book.  Late in the 19th C., after case bindings became prevalent, I hypothesize that their movement influenced bound books. In earlier binding structures, when the boards are opened, the spine also begins to move. When a cased book is opened, the front cover, for example, can be opened  more than 180 degrees without any motion being transfered to the text block.  Late 19th C. bound books move the same way.  At this time, if the board of a bound book was opened fully, it was considered shoddy workmanship if the flyleaf moved at all.  I I wonder if it was the public, bibliophiles or the binders who desired this new type of movement from a book.    

The late 18th C. marked the end of the leather bound book as vernacular culture, and the cased book radically changed the nature of bookbinders work.  Mechanization, repeatability, perfect 90 degree angles, reliance on adhesives rather than mechanical strength, interchangeability of a text and cover and the speed at which the binder had to work all came to the fore at this time. When making an in-boards binding, the craftsman has a sense of constructing or building the book, rather than simply gluing it together.  Since the text and boards are ploughed at the same time, slight deviations from 90 degrees are much more acceptable that in a case binding, where difference would be diasterous if the turnins aren’t even with the boards.  The bookbinder, previously an artisan was increasingly becoming a worker.   And he was forced to emulate machine made standards.

In a roundabout way, all of this points to the importance of studying the tools and machines that made books, in order to better understand small, specific historic details and larger picture- how books have informed the human experience.

 

On Sept 2, 2008 Thomas Conroy added:

I’ve been looking at early binding equipment, and some of the six or eight 1824-1836 patents for “paper cutters” listed in my write-up on the guillotine may have been for board shears rather than guillotines. It isn’t easy to find out, since the Patent Office and all its records burned in 1836. 

Click here

But the rotary board cutter was already in use by 1856, since an engraving of one appears in the edition of Pilkington’s “Artist’s Guide and Mechanic’s Own Book” that also has an early engraving of the roller backer:

Click here

The rotary board cutter would satisfy the edition binder’s need for squareness better than the board shear, so perhaps the board shear’s ability to cut square was less important than you suggest. In any case, do we know when board shears were first equipped with gauges? I don’t think early guillotines had them, and there were still guillotines being sold with only one side gauge into the 1890s.

 

March 20, 2009

I noticed that in Nicholson’s Art  of Bookbinding, both the 1874 and 1856 editions have a picture of a man at a “Table Shears” on page 175.  It doesn’t have gauges, as you mention, but it is in the section of the book that deals with cloth work, not in the section on bound books.