Brent Beach asked for "A bit further explanation, please." I'm going to break my
reply up by his questions. It gets long, I'm afraid.


"What kind of a knife are you using here - what shape, length, bevel angles?"
      I work normally with an English paring knife for beveling the edges of
leather for a cover (on the inside), and with a modified spokeshave for overall
thinning of the leather. The English paring knife is pretty much like a
cabinetmaker's skew chisel, but less than 1/16" thick overall, perhaps 1-1/8"
wide (give or take a bit), and often made without a handle. Mostly I use knives
made by Barnsley before they closed
http://www.hewitonline.com/English_Paring_Knife_p/tl-070-pk.htm

 but Hewit found another firm that copies the Barnsley knives almost exactly. I
normally hone to roughly 18 degrees (1 rise to 3 run), but Jeff Peachey who
makes boutique binders' equipment normally hones to, if I remember correctly, 15
degrees, perhaps less. I grind back the primary every once or twice I hone.
Barnsley knives are surprisingly soft, perhaps as low as Rc54, but this means
that they are also comparatively easy to resharpen, and I like the trade-off.
Jeff Peachey goes in the modern direction of exceedingly hard steel, which most
amateur binders love because they have never before used a sharp knife and it
holds its edge, but the hard steel is correspondingly dreary to sharpen and
tempts you into trying to work for too long with a dull blade. My opinion that
leather takes off an edge quickly is not based on the soft Barnsley knives
alone, by the way, but more on spokeshave blades where I have a direct
comparison between use on wood and use on leather.      A 151-style spokeshave
can be used for leather out of the box, but many (most?) experienced binders
lower the bedding angle from 45 degrees to as little as 31 degrees, open the
mouth out to allow leather shavings to pass through easily without clogging, and
there are various other tuning points, some of which also apply to spokeshaves
for wood. For leather the blade should be honed to, again, 15 or 18 degrees at
most, and this means that the ground bevel must be wide. I hollow-grind my
Stanley/Record blades with a bevel 1/4" wide, on Hock I grind 3/8" wide due to
the extra thickness of the blade. I was taught to keep and sharpen blades in
batches, so that when a blade goes dull halfway through paring a cover you can
go on working with a fresh blade without completely changing gears for
resharpening. For years I used Stanley and Record blades (bought early in my
career) at work, and my good Hock blades at home; when it finally got through to
me that this was backwards I changed and used just the Hock blades at work. With
the chrome-vanadium Stanley/Record I generally had half-a-dozen in my working
batch, but with Hock I found that three was enough. For Barnsley paring knives I
kept four to six going at any one time, with a few older and better knives for
special use.
      I also have a little knowledge of the Scharfix and similar paring
"machines" (they are more like big jigs) which offer some less-subjective
evidence on how quickly leather dulls an edge.

https://www.youtube.com/watch?v=_c8hIzkJlAs

These come with special blades, but are normally used with double-edged razor
blades, which are normally discarded after taking off two or three strips of
leather, say about 40" total length. I know one highly skilled binding teacher
who buys her razor blades by the thousand-blade box, because that lets her get
the top quality blade of her preference. You can buy special blades for the
Scharfix that come sharp, but they cost about 40 cents each. A Scharfix appeals
to many binders because it seems to reduce the amount of skill needed for paring
leather (it doesn't really, but that is another matter), but the big draw is
that you don't have to do any sharpening at all. And a Scharfix comes with a big
price tag, for the machine (about $400.00 new) and for blades.
      There are other tools used by German, French, and other style binders, but
the principles are the same. The shoe industry uses genuine (powered) tubular-
bladed paring machines, and these have a built-in grinding wheel for
resharpening, in some brands running in constant contact with the blade.


"How exactly do you strop the knife? How do you hold it? How many strokes on the
rouge?"
     I normally start with the rouge (hardware store stick) charged on flesh-
side leather glued to a flat board held flat on the bench; I stroke five times
on the flat followed by five on the bevel, being careful not to pull up and
round the bevel on the turn; repeat five; then three on each side repeated; then
one each two or three times. Then repeat on uncharged grain-side leather. It
sounds like a lot, but it actually takes very little time (OK, I shortcut it a
lot of the time, strop a third or half that much on many stroppings), and I am
normally thinking what to do next while I do it. The big danger is allowing the
blade to drift up at the end of the stroke, rounding the edge, and this danger
becomes acute when you go from stropping the flat to stropping the bevel. The
danger of rounding can be reduced by turning the blade over "over the back,"
lifting the edge first from the surface, rather than over the edge in the
instinctive manner, and this is what I teach; but I learned about the technique
too late to work it into my habits. Stropping on the uncharged grain size does
make a perceptible difference in the ease of use of the knife; after rouge alone
the knife may be usable, but it will be cranky and intractable, not sweet-
cutting.      The bevel side of the spokeshave can be stropped without
disturbing the setting by pulling it backwards toward you over the strop, and I
used to do this with Stanley/Record blades, but I don't bother with Hock blades.
The problem with stropping the spokeshave is that taking the blade out disturbs
the setting, and once you have it out you might as well do a thorough job of
sharpening. So blades must be sharpened frequently when over-all thinning
leather, no way around it. Leather of different colors (i.e. different pigments
or dyes) differ in how abrasive they are to the blade, but with most black
leathers and with alum-tawed skin (whitleather, i.e. white, to the Elizabethans)
a spokeshave blade may go dull while thinning a single 12" x 18" piece for one
cover.
 

"What is the paring action? What does 10-25 inches of paring mean?"
      Edging with the knife bevels the leather down from the full thickness as
supplied down to nothing, over about 3/4". The edge moves directly into the
skin, removing a strip the full length of the edge. The skew bevel is necessary
to allow the knife to cut; if you try paring with the knife edge at right angles
to the leather edge, it will hang up and refuse to cut, no matter how sharp it
is.  Here is the video of Jeff Peachey doing a nice job of paring an edge,
already linked to above:
https://www.youtube.com/watch?v=QB5ZHNdqTPQ


Jeff is apparently paring with the tip of the knife along the left edge of the
cover as it rests in front of him (one of the legitimate choices, but possibly
the filming angle is deceptive and he is paring left-to-right on the far edge).
Notice the ease and evenness of the stroke, and that the strips of leather come
off intact, and that he gets an even bevel about 3/4" wide with just the knife.
Taking the three strips off gives a rounded shape to the pared area; a single
sharp arris would leave a visible ridge on the outside after the leather is put
on. Further blending of the slope can be done with the spokeshave. I was taught
to edgepare with the heel of the knife-edge on the right side of the cover,
pushing away from myself; I still teach this way, since there is a conceptual
clarity about controlling the angles when paring with the heel (picking up the
terms pitch, roll, and yaw from aviation). In practice I usually pare with the
tip from left to right along the far edge of the leather, which I think is
easier once you have the conceptual understanding of the ways the edge can tilt.
      I found another video, however, that is rather more instructive than the
one of Jeff paring, since the guy who made it is not highly skilled with the
knife (the actual demonstration of paring, as opposed to hot air, runs from 2:08
to 4:50):

https://www.youtube.com/watch?v=GKQNVC_l0OQ
He does OK on the first strip, certainly at first, but notice that he has the
forefinger of his left hand on the blade. This means that he is pushing the
knife to get it to move at steady speed and angle, and this means that the knife
is not quite sharp. Sharp enough to work with at a pinch, but not sweet, not
sharp enough to use with ease or pleasure. Things go to pieces on the second
stroke, where he is taking off the arris left by the first stroke; from the
beginning it is fluffy-edged and narrower than the first strip (notice that each
of Jeff's strips was wider than the last, and precise). Within four inches of
the start of his stroke, the leather removed is breaking up into dust; and as he
goes on, an educated eye can see that his edge wobbles up and down, leaving
something akin to a chatter on a large scale. I think he is using an old
Barnsley knife, and he didn't strop it between strokes. Things really go to
pieces at the end, where he is trying to thin and clean up the corner of the
leather; by this time the knife is so dull that it will barely cut, and will
only scrape a bit of dust off with each stroke.      I said this guy is not
highly skilled with the knife; well, in fairness, he is probably more skilled
than eighty or ninety per cent of bookbinders. And he does seem to be a
professional. He does a nice enough job of demonstrating round bible corners in
leather at the end of the video. But he doesn't pare well, and it is because he
doesn't know how to strop----in what I called the "hot air" part of the video,
and he makes stropping moves with his hand around 1:10-1:12; these show that he
habitually rounds the edge while stropping, dulling the knife. You can work
around poor skills, but it ain't fun.

One more video is useful in showing how not to do things:
https://www.youtube.com/watch?v=qK6hb7pcjcU

This guy is a general leatherworker, and I'm not going to judge his skill at his
own craft and by comparison with others of his kind. But he doesn't know how to
sharpen and he doesn't know how to pare ("skive" to saddlers and other heavy-
leather craftsmen). Notice that he uses a sawing back-and-forth action. Instead
of pushing one section of the edge along the leather, he runs repeatedly from
the tip of the knife to the heel. This is a classic way of getting a dull knife
to cut in some degree; the problem with it is that you have little control, and
it takes far longer than it should. In fairness again, he is working on salvaged
leather that is probably thicker and harder than binding leather, andd he may be
fighting glue residues and old thread in the visible sewing holes. As with the
previous guy's failure to strop, you can get a knife to work this way, sort of.
      Since paring isn't the only thing you do in binding, you can be a very
good binder and not have good paring skills. Laura Young, one of the most
successful book restorers and binding teachers of the generation before mine,
never learned to sharpen or pare, as shown by her frequently republished manual
on binding (and I have had her deficiency confirmed by a number of my friends,
many of whom were her students). Young described the sawing -action type of
paring for occasions when a knife couldn't be avoided, but her basic advice was
to get a Fortuna skiver, a heavy-duty industrial machine that costs (now)
$1500.00 new and sprays grinding swarf over the freshly-pared area (this doesn't
matter in a shoe that will be trash in a year, but does matter as the life of a
book stretches from the decades to the centuries). So you can be a very good
bookbinder indeed without being able to pare skillfully When I entered the
field, many San Francisco fine binders would send their leather to France to be
pared professionally, much as San Francisco miners of the Gold Rush would send
their laundry to China. I still think you ought to be able to do your own work,
and do it well.

OK, I'm exhausted, and if you aren't as well, I'm surprised. My vile antiquated
PC with vile Microsoft hardware and vile Yahoo that I chose for my email many
years ago are between them crashing about every forty minutes, which means that
I've spent a good many hours on this. Lord, return me safely to Apple, with up-
to-date software. Brent, many thanks for asking such clear and well-organized
questions, which have made it much easier for me to answer with (I hope) a
degree of clarity and organization.

Tom ConroyBerkeley