Visualizing the Touch, the Feel of Parchment

This week’s post is about synaesthetic data.  Literally, it’s about visualizing the data we (the human instrument) collect by touching. To really show you what I mean, I’m going to jump right into our visualizations, which (as discussed last week) are a different style of data visualizations, but they are such nonetheless.

To put what I mean in perspective, I’m going to use something I know you’ve touched, and something you may have touched (the likelihood of which increases significantly if you’re a medievalist working on manuscripts). I’m going to compare the two materializations of post-calf and post-goat flesh we know as leather and (loosely) parchment.



CalfLthrHairImg GoatLthrHairImgCalfLthrHairImgNC GoatLthrHairImgNC                     Calf                                                                     Goat


CalfLthrFleshImg GoatLthrFleshImgCalfLthrFleshImgNC GoatLthrFleshImgNC              Calf                                                                      Goat

In both the flesh- and hairside images, you have sets of the regular image and the image with increased contrast. What you are looking at here shows you a clear distinction between the grain side of leather    CalfLthrHairSmpl GoatLthrHairSmpl and its fleshy backsides.                                                       CalfLthrFleshSmpl GoatLthrFleshSmpl


What you can clearly make out in the magnified images is the differences in texture between the grain side and the flesh side of a piece of leather.  The differences between sides seem to matter much more to both the touch and the visual image of the surface than the difference between either animal, though we can see differences in texture and follicle placement between calf and goat skin.

Make sure to note, that the finer quality of the calf skin, isn’t merely a property of the animal, though; it is also a property of its age.  Full grown cows are likely to have coarser hairs and hairsides, just like a full grown goat.

In both cases, however, we can see that tanned hides retain several features of skin important to the product. We can very clearly see, even in the un-magnified image, the difference between a hair and flesh side, and we are accustomed to this difference in our mundane interactions with leather.

But, I also want to point you to the visible suppleness of the leather, specifically on the flesh side.  What you can see in these images is aCalfLthrFleshImg tangled mass of fibrils (metafibers made up of collagen fibers twisted together) that are curled and twisted up and around each other.  The space between the fibrils, and their curly arrangement is what makes the hide soft, not only to the touch, but also to manipulate.  It moves, bends and stretches (a bit), just like skin, and that is due largely to this structure of these tangled fibrils, that are themselves tangled collagen fibers.

We’ll contrast this to parchment images that show us what happens to the fibrils, and even to the collagen fibers themselves during the process of stretching and drying the wet hide.


In this comparison, to facilitate adding sheep parchment, I’ve reversed the direction of comparison (and am not including any no-contrast images).  On the left are the hair sides of calf, goat, and sheep (in order), and on the right are the flesh sides.

CalfSRHairImgCalfSRFleshImgCalf GoatSandHairCImgGoatSandFleshCImgGoatSheepSRHairCImgSheepSRFleshCImgSheep   Hair                                                               Flesh

What you can clearly see here is the effects of stretching upon the same material.  In each of these images, you can clearly see that the curly tendrils that made up the leather (above) have been stretched and flattened, even aligned. That’s right, in the process of making parchment, the collagen fibers within the skin of the animal are brought into alignment.

In the process of liming, the polar side chains (i.e. the molecules with a charge that hang of the amino acid chains that make up collagen) are able to bond with acid or alkali. The acid or alkali causes water to flow into the fibers to compensate for the new ph balance, causing the whole structure to swell. The fiber weave is thus being weakened both by the chemical bath and by the presence of the additional water.

Now, both leather and parchment go through the liming process. When leather is taken out of lime and the lime and water removed and the hide is tanned, this broken down collagen structure results in the soft, supple quality of leather, and in that tangled web of broken fibril weave we saw above.

In parchment, though, when the hide dries, all those open spaces (opened up by water uptake in liming and soaking) close right up when water evaporates.  The surface tension of water pulls on the capillaries and snaps them shut.  If too many of these capillaries collapse, the hide becomes translucent and brittle, and it shrinks up. Which is why to make parchment, you also need stretching.  As the parchment is stretched, and treated, fewer of the capillaries close up, leaving the hide with both opacity, flexibility, and strength, even while it gets significantly thinner.  It is the sticking that makes a firm, strong, thin sheet, but it is the gaps that make it opaque and flexible.

In the images above, you can see the affects of the stretched, aligned, and systematically closed up fibers in the textures of both the flesh and hair sides of the pieces. (I should note that not all these pieces have gone through exactly the same processes, and none of them are finished parchment ready for manuscript making. The Calf and Sheep parchment have been sanded and re-stretched, but the goat has only been sanded. Nonetheless, you can still see the affects I’m pointing out.)

The images above were chosen because of the clarity with which you can see that process of stretching and aligning in these particular magnifications of the surface textures on these pieces.  However, a number of different factors affect whether or not the effect of stretching is so visually dramatic in the magnified images. (We know it’s visually dramatic just by looking at a full-size piece of parchment.)

Different animals display different textures:

CalfCallHairBImgCalfCallFleshBImgCalf  DeerHairAImgDeerFleshAImgDeerGoatUnHairImgGoatUnFleshImgGoatPigHairAfImgPigFleshAfImgPig SheepSRHairImgSheepSRFleshImgSheep Hair                                                                Flesh

Different portions of the SAME piece can also display different textures

Take for instance this piece unfinished calf we looked at last week or this piece of calf neck that is closer to being finished writing parchment.

CalfNeckFleshABC On this piece, I’ve designated three different areas of interest, and investigated them on both sides:

CalfNeckHairAFatCalfNeckFleshACalfNeckHairAImgCalfNeckFleshAImg Hair A                                                                  Flesh A

CalfNeckHairBSpineCalfNeckFleshBSpineCalfNeckHairBImgNCCalfNeckFleshBImg Hair B                                                                  Flesh B

CalfNeckHairCCalfNeckFleshCCalfNeckHairCImgCalfNeckFleshCImgHair C                                                                 Flesh C

If you were paying attention, you noticed that the flesh sides were all really similar (here they are again in ABC order).CalfNeckFleshAImgCalfNeckFleshBImgCalfNeckFleshCImg


But the hair sides demonstrated significant differences.  CalfNeckHairAImgCalfNeckHairBImgNCCalfNeckHairCImg

A and C aren’t too different, but the hair side around B, the spine, shows a clear pattern of follicles, a direction of fibers, and is actually a no contrast image because the follicles were so easy to see.  You can still see the stretch in A, but in C it’s almost impossible to detect.

All of these differences are detectable to the touch, which is why I marked the different sections for closer scrutiny: because I could feel the differences between A, B and C. Sometimes I could see them too, but not always.

Of course, these differences all but disappear the more the manuscript is finished.  In an example of particularly high grade parchment, made to Pergamena’s highest standards of manuscript finish, hair and flesh sides are almost entirely undetectable:

CalfMSHairAImg CalfMSFleshAImgACalfMSHairBImg CalfMSFleshBImgB  Hair                                                                  Flesh              CalfMSFleshAB In this instance, the A and B sites were chose based on a visible difference.  B is (once again) on the spine of the animal, while A is in regular hide. This time, however, though we can see this distinction on the macro scale, you could neither feel it nor visualize it with a magnified image. Which, I suppose, goes to prove the old adage that

                      looks can be deceiving.

So what is the difference between my photographic image and the visualization of the manuscript’s surface? Well, one tells you precisely what your eye might see (if it were a perfect eye, connected to a perfect memory and visual processing center), while the other tells you what your eyes would miss–what you would only be able to feel with your fingers. This visualization of the texture of a parchment surface allows me to communicate the touch, the feel, of the parchment, even in the parchment’s absence.



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