Hi there! I'm a materials scientist fascinated by the behavior of fountain pen inks on different papers. Yesterday, I had the opportunity to look at some different papers under SEM (scanning electron microscope). I didn't look at the inked paper sample, (because I was concerned about dryness), but am hoping to do that with my next run. 

Image descriptions:

\- #1: a 500x SEM image of Tomoe River 52gsm, taken at 5 kV on a Hitachi TM3000. Uncoated sample cut from a sheet and adhered to carbon tape on an aluminum SEM stub 

\- #2: 5 dip pen writing samples on Tomoe River 52gsm, paper positioned roughly perpendicular to the overhead light, to give minimal surface light reflection

\- #3: same paper aligned to face the overhead light more, to give increased surface light reflection 

My observations: Continuous, relatively thin cellulose fibers appear to be randomly oriented in the paper. Particulates (possibly filler) with high z-contrast are scattered on the cellulose fibers, with some aggregation observed. In some regions I can more clearly see a thin coating of material over the fibers. This material has similar z-contrast to the fibers so I'm thinking it's some sort of organic compound that's not just on the surface, but also impregnated into the fiber matrix.

Contextualizing the paper's behavior with likely nothing new: The low porosity due to a flat, compact coating allows ink to dwell longer on the surface, which promotes the sheening effect. Perhaps the relatively flat surface also lends itself well to strong shimmer behavior, since shimmer particulates in the dried ink would tend to reflect more light because they are more favorably oriented.

Overanalysis for the sake of it: SEM's operation depends on interactions of the material of interest with a rastering electron beam. Z-contrast (i.e. relative brightness of features away from their edges) can give us clues as to the atomic composition of areas in the image. Because higher weight atoms have more electrons to scatter the electron beam back toward the detector, they appear brighter than lower weight atoms. What this means is that the filler is made of some higher atomic weight material. I'm guessing we're possibly looking at an inorganic filler like calcium carbonate (CaCO3) based on appearance.

I'll be sharing more posts in the coming days with my observations for the other papers (Yupo Translucent polymer "paper," plain ol' notebook paper, watercolor paper, and tracing paper). Please let me know what you think, and if you have any questions!

Also as a disclaimer: This is all just analysis for fun, so if I get things wrong please let me know so I can learn too! This is not my particular area of expertise as I'm not a professional paper researcher, fountain pen ink researcher, or the like 😅

Tomoe River 52gsm SEM image: structural analysis and behavior interpretation