An overly smooth surface lacks paper-like friction and makes strokes easy to lose control of

What it is

Paper fibres give the nib continuous tangential damping, which people use for tiny brakes and turns. Polished glass has almost none of that damping, so the nib skates: it keeps going when a stop was meant, and slides through an arc when a turn was meant. Loss of control is not a recognition error and not a latency gap; it is missing mechanical resistance, so the path is longer and straighter than intended.

Why it happens

Fine writing corrections rely on a proprioceptive gradient of resistance: press a little harder and paper bites at once, so the hand knows “braked”. On low-µ glass the gradient is shallow; the same extra force barely raises tangential force, and the brake signal is weak. Fast small characters, hooked strokes, and box lines that must stop on a corner overshoot most. People adapt: slow down, raise normal force to “buy” friction, or write larger to need less precision—adaptations to smoothness, not preferences. Smoothness also brings a visual cousin: specular glare makes the nib harder to fixate, so loss of control is under-read as “I could not see”. High refresh and low latency still skate on smooth glass; what is missing is mechanical damping, not time.

Studying it

Do the same hard stops, hooks, small characters, and boxes on polished versus frictional surfaces. Change only the surface, not the nib.

Independent variables: surface µ, task type, whether people may slow down. Dependent measures: overshoot length, box-exit rate, whether natural speed drops, “slippery”.

If speed is free, the smooth group often slows and quality converges, but time grows—log speed as a dependent measure.

Where it stops holding

Large washes and signature-like long strokes sometimes benefit from low friction. With gloves already blocking shear, a little extra slip matters less. Local slip from oil is not material smoothness: it must still slip after wiping to count as the surface. Extremely high-µ film feels harsh and tires the hand; more drag is not always better.

Applying it

• Do not default writing devices to showroom-polished glass; offer etched glass or a paper-like film, and say it trades a little sharpness for drag.
• Demos must include stops and small hooks, not only slow large letters.
• If polish must stay (a demo unit), expect slower writing or ship a film.
• How to check: in the same time, write small hooked characters on polish and etch; polish should show both overshoot and slow-down. If the difference survives wiping, it is the material.

Related

• Same group: C5.13.1 Screen friction sets nib resistance · C5.13.3 Nib material and screen friction jointly set feel · C5.13.4 Feel is subjective and cannot be captured by latency and accuracy alone
• Adjacent: C5.08 Inking Latency · C5.01 Pressure Sensitivity
• Search: low friction · stroke overshoot · glass too smooth