Identification of fountain pen ink properties which determine the amount put on paper during handwriting

Handwriting with a modern fountain pen is an unique experience in present time, far beyond the pure necessity of making notes. The differences to ballpoint pens, rollerballs or pencils are in the tactual perception of the nib gliding over the paper surface and in the visual impression of a freshly drawn ink line with all the colour impressions and changing light reflections when a wet line dries and reveals either shading or sheen. This subjective impression of the wet line is commonly described as ink wetness and a lot is discussed and speculated about why one ink writes „wet“ and another „dry“. While such a subjective impression can not, the amount of ink put onto the paper can be measured quantitatively. To that end, a number of commercially available fountain pen inks were used to draw lines of a certain length and the amount of ink laid down on the paper was measured. These ink consumption data were correlated to the physical and chemical properties by a principal component analysis. The most significant outcome was the primary dependence of „ink wetness“ on surface tension, followed by viscosity and conductivity with unexpected and partly counter-intuitive correlations.