Introduction

Throughout Europe, parchment was the dominant writing material until the spread of paper in the 14th and 15th centuries1, though it persisted in niche environments for far longer. Parchment documents significantly contributed to the development of cultural heritage and, among other aspects, diplomacy2,3. From Late Antiquity (from 5th to end of 7th century) until modern times, however, parchment production has evolved significantly in terms of manufacturing methods and preferences for the types of animal skins used4.

Its manufacture involves a series of physical and chemical treatments, including lime soaking, dehairing, stretching under tension and mechanical thinning5,6. This process transforms raw hides—typically from sheep, goat or calf—into a stable, durable writing medium rich in fibrillar type I collagen7,8. The resulting material is structurally distinct from papyrus or paper9, offering enhanced mechanical strength10, flexibility and visual aspects, such as opacity and whiteness, which allowed for double-sided writing and long-term preservation.

The hierarchical structure of parchment material is inherited from the skin’s native organization. Animal skin is composed of three primary layers: the superficial epidermis, the central dermis, and the deeper hypodermis. The dermis itself is subdivided into the papillary layer, composed of fine and loosely arranged collagen fibrils, and the reticular layer, characterized by thicker and more densely packed fibers8,11. The papillary-reticular junction is structurally heterogeneous and includes blood vessels, lipid deposits, and a transition in fiber morphology12,13. During conventional parchment manufacture, both the epidermis and the hypodermis are removed resulting in two distinct sides: the grain side (deep papillary dermis) composed of finer, more tightly packed collagen fibrils, and the flesh side (reticular dermis), containing a coarser and more disordered fibers organization8,14,15,16. Under mechanical tension during drying, these fibrils are reoriented8,11 and compacted, forming a lamellar, anisotropic structure that impacts mechanical strength and durability8,10. As a result, parchment is considered as a collagen-based composite material, with intrinsic heterogeneity inherited from the original skin.

Delamination is the phenomenon by which internal layers of the skin separate along their interface. In layered materials, in general, it can be caused by free edge effects, structural discontinuities, local manufacturing defects, variations in temperature and humidity conditions, internal failure mechanisms or external stresses17. Parchment produced from sheepskin is particularly prone to delamination11,13,18, making erasures and alterations more apparent18,19. The preferential use of sheepskin over calf or goat skin may have emerged from early attempts to prevent falsification of legal documents. Delamination is also referred to as the skin’s tendency to “split”5,20. The peeling-off process refers to the action of detaching the superficial layer from the skin. The practice of splitting animal skins into two usable thin parchments was already established in the early centuries AD20,21. Loose pieces left by the peeling can be used to repair holes on the parchment surface6,22.

The delamination process could take advantage of the natural separation plane between the papillary and reticular dermis, where a fatty interface facilitates mechanical division11,12,13,18. During the parchment manufacturing process, fats surrounding follicles move outside their envelope. Consequently, their presence at the reticular-papillary junction could be due to hair follicles originating there. The removal of lipids, from the sebaceous glands associated with hair follicles, during parchment production (saponification of triglycerides during liming) is believed to favor the separation of the two constituent layers of the dermis. The particularity of the delamination process for sheepskin is highlighted through its different skin structure11, which link high fat content in comparison to other animals12,18 to the great number of main and secondary hair follicles23,24.

Historically, parchment makers took advantage of delamination during the production of Late Antique manuscripts. In fact, the production of parchments involved, at the time, a distinctive peeling process during the wet phase of production. After lime soaking and dehairing, the epidermis layer was physically peeled off from the grain side of the skin with the papillary dermis beneath it. This was typically done while the skin was stretched on a frame, facilitating a smooth separation of the upper layers from the reticular dermis. This peeling process, rather than abrasive scraping, enabled the production of parchments that were exceptionally thin, smooth, and white on both sides (Fig. 1a). As a result, Late Antique parchments often show minimal difference between the hair and flesh sides. The peeling method not only enhanced writing quality but also contributed to the material’s translucency and flexibility. The removal of the upper skin layers also explains the absence of hair follicle patterns and natural pigmentation, which were typically lost in the process. This uniformity across the surface, combined with the parchment’s minimal thickness suggests that peeling was a carefully controlled and intentional technique unique to this period and style of parchment manufacture6.

Fig. 1: Pictures of MS Laud Gr. 35 manuscript, dated to the 6th or 7th century (Italy), preserved in the Bodleian Library (Oxford)60.
figure 1

Detail of the front margin of folio 28r (hair side): the parchment exhibits several incomplete attempts to peel the superficial layer of the sheepskin. In some areas, the partially peeled layer is folded back (a). Patch of peeled skin reattached as a repair over a hole in the lower corner of folio 22r (hair side) (b).

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Parchment makers employed a rapid repair method using freshly removed tissue as patches22 to cover newly formed holes, which suddenly appear during the peeling process on wet (stretched) parchment. Kept in water for a while, these so-called epidermis patches were applied while the skin was still wet and under tension. These transparent patches were placed on the hair side of the parchment, without adhesive (Fig. 1b). Once dried, these repairs formed a strong, integrated laminate capable of withstanding further stretching and manipulation. Though extremely thin, the patches were durable enough to be written or painted on.

Several studies using different techniques have reported observation of collagen fibers on the surface of parchment (scanning electron microscopy25,26,27, atomic force microscopy26,28,29 or non-linear optical microscopy15). Cross-sectional imaging can reveal the internal structure of parchment30,31,32,33. Scanning Electron Microscopy (SEM) observations of parchment cross-section enable the evaluation of morphology and composition using, respectively, secondary (SE) and backscattered (BSE) electron detection modes. Raman spectroscopy has previously been applied in cultural heritage34,35, among others, to assess deterioration in aged parchment9,36,37,38,39. Raman spectroscopy has also already been used to characterize the human skin structure (epidermis, dermis)40 and the distribution of specific elements such as keratin41 or melanin42. Information on spatial variations of chemical composition in the parchment can be obtained using micro(µ)-Raman imaging spectroscopy43,44.

Parchments are testimony to ancient practices and craftsmanship. The delamination observed in sheep parchment, compared to that made of other animals, raises important questions about historical material selection and processing techniques. Understanding why sheepskin behaves differently under traditional preparation techniques offers valuable insights into the interplay between animal biology, craftsman’s work and historical needs. Delamination has been previously reported and described in the literature. However, a comprehensive investigation into its underlying causes and the above-mentioned implications remains lacking. By combining experimental archeology with modern analytical techniques, the present study intends to clarify why delamination of sheepskin parchment is inherent to that species. Our investigation attempts to identify the delamination site in the processed skin structure and to gain a deeper understanding of the bonding process of the patch on parchment. For this purpose, samples from a delaminated sheepskin parchment were analyzed by SEM and µ-Raman spectroscopy. These techniques could not be applied to original Late Antique manuscripts. For this reason, we recreated experimentally delamination and patch repairs in a contemporary produced parchment. This study also investigates the surface properties of delaminated sheepskin to assess whether they contributed to promote the use of sheepskin for prestigious documents. To our knowledge, experiments involving sessile droplets on parchment have never been reported in literature.

Methods

Experimental recreation of delamination and patch application

One parchment from stillborn black haired lambskin was processed during a workshop in Klosterneuburg (Austria) in 2023, organized by the European Beasts to Craft (B2C) project6. Previously frozen, the lambskin was washed under running water. It was then immersed in a lime solution for one week to initiate the unhairing and loosening of epidermal layers. The dehairing and the first removal of residual material from the flesh side on a wooden beam preceded its attachment to a circular frame, stretching the fibrous structure and facilitating the splitting process6. The skin was peeled off on the hair side, except on the borders, using a flat bone (Fig. 2a), non-cutting blade or by hand (Fig. 2b). After being immersed in water, some loose pieces were retrieved and placed on the wet peeled-off skin (Fig. 2c). The flesh side was scraped to clean the skin from impurities (Fig. 2d).

Fig. 2: Experimental recreation of delamination.
figure 2

Peeling-off of lambskin parchment on the hair side with a non-cutting blade (a) or gently by hand (b). Freshly applied patches on different areas of wet skin (circles) (c). Flesh side after scraping and drying (d). Grain side after peeling-off process: fragment of skin made available for the study (box) and patches (identified with the letter P) placed on a delaminated area (e). Piece of parchment used in this work: accidentally folded (identified with the letter F) delaminated pieces, the patch (identified with P), the cut samples used for SEM observations (black boxes) and their numeration, location of SEM cross-section observation (red line) (f).

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A piece of this skin was provided for the study (Fig. 2e). The main part was delaminated except for the darker upper border. While the material was still wet, pieces that had partially peeled off stayed attached to the skin instead of being removed, accidentally sticking to the non-delaminated side (Fig. 2f). An area of the delaminated hair side is covered by a patch made of peeled-off skin. Once the parchment was dried, the thickness difference between the patched and non-patched parchment was minimal, making it seem embedded in the underlying structure. Additionally, no traces of hair follicles are apparent on the delaminated region.

Experimental recreation of ferrogallic ink

Ferrogallic ink was produced using historical recipes45 during a dedicated workshop, under guidance of Franck Bonnois, craftsman (Provins, France). First, arabic gum put in a cloth bag to retain impurities, was dissolved in warm water. Long before the experiment, crushed oak gallnuts were macerated in hot water for several months, allowing the mixture to be exposed to air and develop surface mold. After maceration, the mixture was heated with the remaining gallnut fragments to reduce its volume, then filtered through a cloth. The final ink was obtained by mixing the filtered extract with gum solution and ferrous sulfate. Upon mixing, the solution turned black instantly.

Scanning electron microscopy

Small pieces were cut from the parchment isolated for the study to observe the different structures within the same cross-section, including the delaminated and non-delaminated parts (Fig. 2f). The purpose of this is to identify the layers involved in the delamination process. The size of these pieces was determined by the experimental conditions and the sample holder used for SEM observations (1.5 cm × 0.5 cm).

Each cut piece was placed in a vacuum chamber at a pressure around 0.01 mbar, one week before the first observations to ensure a suitable vacuum in the SEM chamber. Before imaging session, samples were sputter coated with a 15 nm gold layer (Quorum Q150T/ES) to prevent charging effects. The samples were placed on a holder and their edges clamped between two plates using a screw system. SEM imaging was performed using a JEOL 7500-F SEM at an accelerating voltage of 5.0 kV. The hair side of the original parchment is the upper face of the sample displayed on SEM images.

Micro-Raman spectroscopy

The micro-Raman spectrometer used in this study was a LabRAM Soleil system (Horiba, France SAS.) with an excitation laser wavelength of 785 nm to avoid fluorescence9,35. No sample preparation was performed before measurement. Calibration of the instrument was performed on the 520.7 cm−1 band of a silicon chip. The power was settled at a nominal value of 63 mW, with a spot size diameter of about 2 μm. Experimental parameters were a confocal pinhole of 500 μm and a ×50 long-range objective lens (NA 0.60). Spectra covering the 800–1725 cm−1 spectral range at once were acquired with a low resolution 600 grooves/mm grating giving a spectral resolution of 4 cm−1, whereas higher resolution spectra were acquired in four successive windows to cover the same spectral range, with a 1800 grooves/mm grating reaching a resolution of 1 cm−1. Photobleaching was performed to attenuate fluorescence effects by exposing the measured spot to the above laser power during 120 s right before acquisition. Data were acquired using the LabSpec 6.7 program. Raman spectra are the average of three raw spectra, each one acquired over an integration time of 15 s. Baseline was removed using Python with a rubber band method using a convex hull46. All spectra were smoothed with a Savitsky-Golay filter47,48 of order 1 and 3 points window for the 600 grooves/mm spectra, and order 3 with 20 points window for the 1800 grooves/mm spectra.

Wetting dynamics experiments

Wetting dynamics experiments were conducted using a Dataphysics OCA35 goniometer. A 3 μL droplet of ferrogallic ink was dispensed via the instrument’s automated system, employing a Hamilton 500 μL syringe. Data was acquired using the SCA20 program. Calibration was based on the external diameter of the dispensing needle. All measurements were performed under the same ambient conditions without prior surface treatment. The program recorded the wetting dynamics of the droplet on film, which was then analyzed. Droplet shape analysis was performed using an ellipse arc fitting function. The experimenter adjusted the baseline position to compensate for variations in surface position induced by absorption. Contact angle, baseline diameter and volume were computed by the program.

Results

Delamination made the sheepskin parchment thinner and produced an incredibly smooth surface compared to non-delaminated parchment. On average, the delaminated areas were up to half as thick as the non-delaminated border areas. Thickness (measured using a caliper with an accuracy of 10 μm) was equal to 0.12 mm in the central delaminated zone, around 0.20 mm in the non-delaminated regions, and between 0.45 and 0.50 mm in the folded, non-delaminated areas. The non-delaminated parchment covered with patch had a thickness of about 0.16 mm. SEM (SE) surface images of sample 3 (Fig. 2f) reveal clearly defined collagen fibers on the delaminated region (Fig. 3a), characteristic of the dermis. Fibers appear to lie parallel to the surface. This contrasts with the rough structure from the borders, in the non-delaminated part (Fig. 3b).

Fig. 3: Electron microscopy characterization.
figure 3

SEM (SE) images of the parchment surface near the delaminated region adjacent to the patch (a), and of the non-delaminated area (b). SEM (SE) cross-sectional image of sample 1 showing three distinct regions: delaminated, folded and non-delaminated (c). High-magnification SEM (SE) cross-sectional image of the delaminated region in sample 1 (d). SEM (BSE) cross-sectional image of the delaminated area in sample 1 (e).

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The sample 1 (Fig. 2f) served as evidence of the delamination process. It resulted from a peeling-off action of a thin layer of the skin, which folded upwards and bonded to the non-delaminated part. This sample features three colors on the surface that denote the varying thickness of the elements. The lightest color indicates a thinner, delaminated element, while the darkest one corresponds to a thicker, folded element. The top part belongs to the non-delaminated region. The observed cross-section (red line, sample 1, Fig. 2f) covers these three components (Fig. 3c). SEM (SE) images of the sample cross-section show morphological differences which clearly define two layers in the delaminated part (Fig. 3d). This result is confirmed by the low-angle backscattered electron detection mode, in which the intensity contrast of the latter image indicates chemical variations (Fig. 3e). The presence of heavier elements (higher Z-values) is characterized by brighter appearance due to their greater ability to deflect electrons compared to lighter elements49. The SEM (BSE) image shows a lighter upper layer and a darker lower layer. Chemical variations between both layers could be due to the difference in penetration of calcium carbonate (CaCO₃), from the reaction of lime used in the parchment making process33. This level of contrast could also be interpreted in terms of the structure of the skin and its remaining layers in the parchment.

In the experiment, the deep hypodermis and a part of all epidermis were removed, leaving the invaginated part, from the hair side. This procedure resulted in collagen type I fibers from the dermis apparent. Therefore, the two layers visible through SEM observation correspond to the papillary and reticular dermis. Separation during the peeling process occurs in the upper papillary dermis. This challenges assumptions that attribute delamination to structural weakness at the papillary-reticular junction. The delamination within the skin structure is instead hypothesized to result from the detachment of hair follicles, which are predominantly situated in the upper position in the papillary dermis. The notably higher number of hair follicles in sheepskin compared to other species commonly used for parchment production, such as goat and calves24,50, partly explain why sheepskin is more prone to delamination. This tendency is further exacerbated by the relatively high lipid content characteristic of sheepskin18.

To determine precisely which layers were removed during the peeling process, µ-Raman spectroscopy was conducted on both the delaminated and non-delaminated areas. A central question is whether the epidermis layer was entirely removed during the steps preceding the peeling, or whether superficial part of it remained and was subsequently detached during the peeling itself. This analysis also aimed to test the hypothesis that calcium carbonate is responsible for the observed contrast by SEM (BSE).

The Raman depth of analysis depends on several factors, including the laser wavelength, the numerical aperture of the objective lens and the optical properties of the material under investigation51. In the case of parchment, under the experimental features employed, the penetration depth is limited to a few microns only37, so that in these conditions µ-Raman spectroscopy can be regarded as a surface-sensitive technique. It is therefore unable to probe beyond the epidermal layer until the collagen-rich dermis, particularly in sheepskin, where the epidermis can be approximately 30 μm thick52. The Raman analysis was focused on the progressive transition from non-delaminated to delaminated area (Fig. 4a). The corresponding Raman features are shown in Fig. 4b. A reference spectrum was also measured in the delaminated region located farther from the parchment edge with higher spectral resolution (Fig. 4c).

Fig. 4: Micro-Raman spectroscopy characterization.
figure 4

Micro-Raman spectroscopy measurements. Position of the junction between non-delaminated to delaminated areas and its microscope image identifying the numbered spots of the sequence of spectra acquired along a line (spots 1–4) and a reference in the core of the delaminated part (spot 5) (a). Raman spectra (600 grooves/mm grating) obtained at the 1–4 spots marked in (a). Spectra number 1 and 2 correspond to the non-delaminated part, spectrum 3 to the transition zone, and spectrum 4 to the delaminated region: the measured vibrational band positions of collagen type I (blue)37,39,40, calcium carbonate (green)37,53, lipids (red)41,42,61,62,63, melanin (brown)42,64 and carotenoids (orange)41,54,65 (b). Reference Raman spectrum (1800 grooves/mm grating) of the delaminated part (spot 5) with measured vibrational features corresponding to collagen type I (blue)37,39,40 and calcium carbonate (green)37,53 (c).

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This latter exhibited a Raman signature characteristic of type I collagen37,39,40, in consistency with the dermis layer40,42. A vibrational band associated with calcium carbonate37,53 is observed at 1088 cm−1, and confirms the previously mentioned hypothesis for SEM (BSE) interpretation. Characteristic peaks related to collagen type I are measured in both the delaminated and non-delaminated areas around the junction, with a progressively higher intensity when going towards the delaminated part (from 1 to 4 in Fig. 4b). The spectrum 3 obtained at the boundary between the delaminated and the non-delaminated regions shows rather intense lipid peaks. This lipid accumulation comes from sebaceous gland secretions, which are abundant and related to both primary and secondary hair follicles in sheepskin (Fig. 5). Rupture of sebaceous glands upon skin stretching is likely to facilitate the spread of lipids, resulting locally in a structural weakness within the papillary dermis. The strong lipid signal observed at the boundary, and its absence in the fully delaminated area, suggest that the delamination occurs most probably along this lipid-rich region (dashed red line in Fig. 5b). In accordance with literature11,18, the lipid layer plays a central role in the delamination mechanism. Besides, follicular voids observed in stretched skin11 contribute to the structural weakness abovementioned.

Fig. 5: Sketch of delamination process.
figure 5

Sketch of lambskin cross-section: pristine (a) and stretched skin just before delamination (b). Pristine skin contains hairs, hair follicles, and sebaceous glands. Stretched skin during parchment processing: epidermis and hypodermis removed, hair extracted from follicles. The red dashed line indicates approximately the depth where delamination occurs, favored by empty hair cavities and fats from sebaceous glands.

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The spectrum 3 presents also signals which could be attributed to carotenoids and possibly melanin, although further analysis is required to confirm this assignment. Melanin, carotenoids, and lipids are molecular species typically localized in the epidermis rather than the dermis, where they are respectively associated with pigmentation42, antioxidant activity54,55, and barrier function56. These measurements indicate residual structures coming from the epidermis on the surface of non-delaminated parchment besides collagen fibers. The peeling process therefore contributes to the removal of residual epidermal layers and a portion of the papillary dermis.

Beyond the visual characteristics of the parchment surface and its thickness, enhanced wetting properties could justify such a peeling-off process for writing applications. Sessile droplet measurements were conducted with ferrogallic ink on both delaminated and non-delaminated regions of the parchment to highlight potential wetting dynamics differences. Sequential time-lapse captured images are presented in Fig. 6, with the corresponding quantitative parameters characterizing the droplet shape. Their precision is primarily influenced by the difficulty of adapting baseline position over time and the accuracy of fitting the droplet profile during image analysis. Despite precautions to ensure a uniformly flat surface, residual shadowing was observed behind the droplet.

Fig. 6: Wetting experiment.
figure 6

Time-lapse images of ferrogallic ink droplets on delaminated and non-delaminated sheepskin parchment at 0 s, 5 min and 15 min with corresponding contact angle (CA), base diameter (BD) and volume measurements. Contact angles result from averaging of the contact angles to the right and left of each sessile droplet.

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Contact angle measurements show that the wetting dynamics is slower in the delaminated part (angle decreasing from 93.0° to 65.0° after 15 min) than in the non-delaminated part (angle decreasing from 105.0° to 55.2° after the same time). Ferrogallic ink spreads better in the delaminated parchment but is less easily absorbed. These observations can be interpreted due to differences in the surface characteristics of each area, with greater roughness observed at the border of the parchment piece than in the central part (Fig. 3a, b). The delaminated region appeared to absorb ink less efficiently, likely due to more compact and aligned collagen fibers, which reduce capillary action. In contrast, the non-delaminated surface is more porous, enhancing ink absorption.

Ferrogallic ink contains iron-gallate complexes stabilized by the polysaccharide binder (arabic gum)57. Arabic gum enhances ink adhesion by forming hydrogen bonds and stabilizing the ink colloidal system58. It also contributes to ink viscosity and prevents diffusion on porous substrates. The non-delaminated region presents a high calcite content, in contrast to the delaminated area, which displays characteristic vibrational spectral bands of collagen type I. Collagen type I exhibits amphiphilic surface characteristics, meaning it contains both hydrophilic and hydrophobic residues59. This dual nature allows it to interact effectively with the components of ferrogallic ink39: hydrophilic residues can form hydrogen bonds with stabilized iron-gallate complexes. In contrast, calcite, with its solely hydrophilic character and slightly ionic surface, lacks reactive functional groups necessary to support strong interactions with the ink components. Its surface chemistry does not favor the formation of stable complexes with the iron-gallate species, resulting in reduced ink wettability and adhesion compared to collagen-rich areas of the delaminated part.

For patch repair testing experiment, samples were placed for one week in a preparation chamber under vacuum, before being coated by gold for SEM observations. Sample 2 presents an accidentally folded part. After 24 h in the preparation chamber, the detachment of the latter part from the non-delaminated border was observed (Fig. 7a). In comparison, sample 3 with the patch went through in total almost 10 days in the preparation chamber and several hours in SEM measurement chamber (9 × 10−7 mbar). While the folded part comes off, the patch stays firmly bonded on the delaminated parchment (Fig. 7b - left). Sample 2 exhibited weaker bonding. Its stay in the preparation chamber contributes to eliminating water involved in intermolecular interactions as the hydrogen bonds. In contrast, the patch demonstrated significantly stronger adhesion. The observed difference in adhesion primarily results from wetting conditions: the patch was completely immersed in water for several minutes before being carefully positioned and pressed onto the substrate, thereby ensuring a strong adhesion.

Fig. 7: Layer detachment and patch adhesion.
figure 7

Photography of the surface (left) and the side view (right) of sample 2 after being exposed to low pressure in the preparation chamber (a). Photography of the surface of sample 3 after being coated of gold and exposed several times to low pressure (left – b). SEM (SE) surface observation of sample 3 of the junction between the patch (bottom) and the delaminated part (top) (right – b).

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SEM (SE) imaging revealed clear topographical differences between the delaminated parchment and the patch (Fig. 7b - right). The surface appears rough and irregular, characterized by a fine suprastructure composed of small protrusions.

Discussion

This study provides a comprehensive investigation into the delamination process of sheepskin parchment, a phenomenon historically exploited in the production of legal documents. Through experimental archeology, we successfully replicated Late Antique parchment-making techniques and repair techniques. This approach enabled detailed characterization through SEM imaging and micro-Raman spectroscopy, providing complementary morphological and chemical insights into the delamination interface.

Our analyses reveal that delamination occurs within the papillary dermis, rather than at the papillary-reticular junction as previously assumed (Fig. 5). The delamination mechanism most probably involves a region of papillary that is structurally weakened due to hair follicle voids, and a fatty layer from sebaceous gland secretions. Moreover, micro-Raman spectroscopy indicates that most of the epidermis is removed during the early stages of parchment preparation, with the peeling-off process eliminating only residual epidermal fragments embedded within the dermis. A non-uniform penetration of calcium carbonate (CaCO₃)—whose presence on the delaminated surface was verified by Raman spectroscopy—across the skin’s cross-section may contribute to the contrast observed in BSE-SEM imaging. The successful adhesion of a skin patch applied to the delaminated surface after exposure to vacuum confirms its efficiency as repaired material used during process of the parchment making. Beyond its visual and structural implications, delamination appears to enhance the surface properties of parchment, improving ink spread and writing quality. The interaction between ferrogallic ink and delaminated sheepskin revealed previously undocumented insights into how surface morphology and composition influence writing performance. Altogether, this work not only deepens our scientific understanding of sheepskin parchment but also offers a material-based explanation for its historical preference in legal contexts, where its tendency to delaminate may have served as a deterrent to tampering or forgery.