Two eyeliner tips can have a similar point size and draw different lines. A tip bends under load, and the liquid can spread after contact. Measuring the line gives you the combined result. A closer look at the contact area helps explain it.
Draw controlled strokes
Use the same formula batch, application surface, priming sequence, stroke length, and measurement delay. Set a consistent pen angle, travel speed, and load. If users are expected to draw with different pressures, repeat the comparison at each chosen load instead of averaging across them. Use several pens from each group and several strokes per pen so one unusual stroke does not drive the comparison.
Photograph each line with a scale in the same plane. Measure the width across the middle at several fixed locations, and record the startup and finish separately. Note broken lines, feathering, and pools of product alongside the measured width. If a line broadens while resting on the surface, repeat the measurement at an agreed early and later time.
A tip that makes a wider mark only at higher load may be flexing or spreading out at the surface. A line that grows after the stroke points you toward liquid spreading on the chosen surface. The observations can overlap. Use a close view of the tip under load and an agreed reference surface to separate them. Report the measured range together with the conditions. That gives the buyer a meaningful comparison for the intended stroke style. The SamBound packaging catalog is available at sambound.com.
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