Brushology: Anatomy and nomenclature
There are basically two parts to a badger-hair shaving brush: a handle and a knot. The photo below shows a cutaway section of a Paladin™ Chief™ shaving brush. Its knot was installed by Lee Sabini in England, who sets knots a little differently than we do, but the difference is not important for purposes of this discussion.
Standard brush specifications
The overall height of this brush is 111.65 mm, with the handle contributing 59.4 mm. Loft refers to the vertical distance from a) the top of a handle where the knot is inserted into the socket (often referred to as the knot hole) to b) the knot’s crown or peak, which, assuming the knot has a dome-shaped top (or canopy), will be at or very close to its center. This brush’s loft, calculated by subtracting handle height from overall brush height, is 52.25 mm.
Loft is the most common and often the only measurement given in description of a brush’s knot besides its base diameter. These two specifications, however, do not adequately serve prediction of how a brush will feel or perform in use.
Several variables can affect the appearance, feel, and performance of a knot. Those include: 1) hair type and quality (e.g., softness, resilience), 2) base diameter (measured at the top of the glue plug), 3) volume density at its base, 4) shape, 5) depth of set, 6) diameter of the socket into which the knot has been set, 7) loft, and 8) free loft. All of these factors in combination influence set-shape (i.e., shape as set in the handle), overall aesthetics, bloom, splay, density, backbone, scrub, scritch, floppiness, moppiness, lather production, lather uptake, flow-through, and drying time.
Below is a photo of two knots (L-type on the left and S-type on the right), both of which were designated for installation in handles with 26 mm diameter sockets. Each of the knots has a yellowish, epoxy base, or glue plug, which secures the badger hair in place.
Although glue plugs typically exhibit a disc-like appearance as viewed from an external perspective, they actually form a dome, the shape of which will roughly correspond with that of the knot’s top (referred to by some as the canopy). This can be seen in the top photo, which shows a glue bump measurement of 10.75 mm. Note that the bump, as measured, extends up and into the hair as far as glue penetrates (thereby fixing the hair shafts and rendering them inflexible, which will consequently affect the knot’s characteristics).
Extensive discussion of glue bumps can be found in shaving-brush forums. But focus tends to be placed on the size of the bump rather that than the length of the hair above the bump. And it’s the length of the hair above the bump not the height of the bump itself that mainly matters.
We’ve introduced free loft as a term referring to the vertical distance from the highest level glue reaches at the center of a knot (i.e., the top of its glue bump) to the knot’s crown (unless the top of the glue bump is recessed beneath the socket rim, in which case a brush’s free loft by our definition will be equal to its loft). A knot’s free loft can be expected to influence the feel and performance of a brush. All else being equal, a knot with free loft of 42 mm set at a loft of 52 mm will be noticeably different than a knot with free loft of 48 mm set at a loft of 52 mm. This isn’t meant to imply that one of those two knots would be better or worse than the other. They would just be different, and observations from use of one might not reliably apply to the other.
Note that we chose to use free loft rather than effective loft by reason of the fact a knot with free loft of 42 mm set at a loft of 48 mm will perform and be experienced differently than the same knot set at a loft of 52 mm, so it would be misleading to imply a glue bump's contribution to loft is entirely ineffective.
Knot measurement and comparison
The L-type knot is about 68 mm tall and has a base diameter of approximately 24.2 mm. The knot on the right (S-type) is barely over 63 mm tall with a base diameter of about 25.2 mm. Note that the L-type knot is glued in the lower, light-colored band (2-band hair actually has three distinct bands, at least before it is cut), whereas the S-type knot is for the most part glued at the bottom of the dark, middle band. More hair can be packed into a given circumference in the lower section than the dark, middle section. This accounts for the fact the L-type knot shown here, despite its smaller base diameter, is a slightly tighter fit in a 26 mm socket than the S-type knot.
Direct measurement of either glue bumps or free loft can be tricky and difficult to do with consistency. We use our laser cutter/engraver to make gauges out of bamboo skewers. They’re not fancy, but they work.
The next two photos show each of the knots with a gauge inserted.
The L-type knot’s free loft measured about 47.5 mm. (The gauge rose a bit in the knot when I removed my hand to take the photo.) The S-type knot’s free loft is approximately 45 mm. A 2.5 mm difference, combined with a couple other comparative knot dimensions, can significantly influence a shaving brushes characteristics.
Since L-type knots tend to be a taller in overall height than correspondingly sized S-type knots, most of them will be set deeper than S-type knots, which can be expected to result in somewhat different splay characteristics, all else being equal. And in our experience L-type knots seem to yield a softer and comparatively less scrubby feel than S-type knots, which we largely attribute to difference in free loft.
On the other hand, S-type knots are generally a little shorter in overall height than correspondingly sized L-type knots; consequently, most of them will be at less depth than L-type, again likely resulting in different splay characteristics, all else being equal. And given that these knots have a bit less free-loft, we weren’t surprised to find that in our use they yield a bit stiffer backbone and scrubbier effect by comparison.
When considering selection of a Paladin Shaving Brush, be sure to take note of the Knot Code in the upper-right corner of the brushes front-side photos (see example below), and the loft and free loft measurements given in the lower-right corner. For information corresponding to the Knot Code, see Knot Notes.