SF-04
Guilloche rosette
The dense interference banding produced by superposing one machine-drawn curve on itself many times over.
Guilloche rosette ×10
Specification
- House code
- SF-04
- Method
- Rose-engine geometry, engraved
- Apparent at
- ×10
- Deters
- Freehand redrawing and imitation by tracing.
- The recipient’s check
- Look closely at where the curves cross. Every line runs unbroken through the crossings and the spacing stays even; nothing is patched, and the pattern never repeats itself untidily.
A guilloche is not a decorative squiggle. It is the curve a rose engine draws: a cutting tool held at a fixed distance from the centre of a small wheel while that wheel rolls around inside or outside a larger fixed circle. The tool traces a trochoid, and the engraver then repeats the same trochoid many times, each rotated by a small constant angle.
What you see is the superposition, not any single curve. The bands and moire that appear where the repeats cross are an emergent property of the ratios the machine was set to, and they are exquisitely sensitive to those ratios: change one setting slightly and the whole figure reorganises.
Why it deters
You cannot draw a guilloche freehand, and you cannot fake one convincingly by tracing, because a tracing accumulates error at exactly the places — the crossings — where the eye is most sensitive to it. To reproduce the pattern you have to reproduce the machine settings, which is a different and much harder problem than reproducing the picture.
The rosettes on this site are computed, not drawn: the same parametric curves the rose engine cuts, evaluated in the browser.