Feature article
Lost and Found among Moroccan Tiling Artworks
No matter their experience or research area, crystallographers tend to have an innate attraction for tessellation patterns. It might be the elegance of symmetry, the reassuring regularity of repetition, or their combination with the natural beauty of imperfections: our fascination for geometrical tiling is arguably a statistical fact. When travelling for scientific meetings or holidays, pattern discovery is rarely a planned activity but rather an unexpected moment of awe. A different case is when visiting a place where tourists gather to witness spectacular tile artworks made with skills and dedication beyond belief. Among the most renowned of such countries and cities we have are those rich in Islamic tessellation art.
Recently, I had the pleasure of attending the second edition of the Mediterranean Conference on Porous Materials in Marrakech (Morocco), and I took an obvious chance to look for fine examples of such artifacts. What is particularly special about Morocco is that traditional Islamic patterns are combined with a tiling style unique to this region. Its name is Zellij, derived from the Arabic word for the verb ‘to slide’ — possibly referring to the act of sliding small tiles in place — and indicates a style of tiling made from individually hand-chiselled pieces. Without the impression of interwoven stripes characteristic of traditional Islamic patterns, the result is a mosaic with homogeneously sized building blocks that combine in complex assemblies featuring various tile shapes and colours (Fig. 1).
Figure 1. Example of a Zellij mosaic (left) and a traditional Islamic pattern (right), both spotted at the conference venue.
While I certainly missed numerous exhibitions and hidden tileworks across the city of Marrakech, I managed to reserve some time to explore the spacious conference venue (Hotel Grand Mogador Agdal) and visit the Bahia Palace in the city centre, which added copious Zellij mosaics to my picture collection. Built over more than 10 years, this sumptuous palace is a mesmerizing continuum of tileworks and stuccos, ready to fascinate any visitor and capable of trapping an unprepared crystallographer for hours (Fig. 2). In the following, I will give an overview of the most remarkable pieces I have captured — and have been captured by.
Figure 2. Casual shots of the composite tileworks decorating essentially every part of the Bahia Palace, from floors to walls, ceilings, fountains, and stairs.
In the eyes of a crystallographer
Based on my knowledge of several young and senior members of our community, the reaction of a crystallographer to geometric tiling patterns always involves asking themselves one or a combination of the following questions: (1) What is the unit cell? (2) What is its plane group symmetry? (3) What would its diffraction pattern look like? Personally, I would also add “Would it create diffuse scattering when Fourier transformed?” and “Where can I find one with 5-fold symmetry?”
During my visit, I was unable to spot any aperiodic tiling containing 5-fold or other non-crystallographic symmetries. However, I did notice something interesting about the plane groups of the mosaics I observed: they were almost always either p4 or p4m, very rarely p6 or p6m. I spontaneously wondered why, especially considering the widely appreciated beauty of 6-fold symmetry (Fig. 3). A simple answer to this question could be that hexagonal symmetry does an excellent job at tiling an infinite plane, but it is not very convenient for tiling finite floors and walls whose area is shaped as a square or a rectangle.
Figure 3. The only two hexagonal symmetries I spotted, from the left-hand side, at the conference venue and at the Bahia Palace (p6 and p6m, respectively).
Figure 4. Six samples of Zellij mosaics found in the Bahia Palace, all featuring p4m symmetry except one rare case of pgg.
Another interesting observation I made about these mosaics is that artists apparently engage in creating intricated artworks that would strictly follow a plane group symmetry if not for a small detail that breaks it — often even eliminating translational symmetry (Fig. 5). Such cases appear to be more systematic the more complex the mosaic in terms of repeating units, number of tiles, or number of colours. I have no doubt that these imperfections are fully intentional, given the precision pervading each centimetre of these tileworks. Since my crystallographic passion is the study of imperfections, such as defects and disorder, I would certainly have enjoyed introducing these 'defects' myself as a playful reminder that no real crystal is ever perfect — perhaps a less likely choice for Zellij masters. Indeed, I discovered not only that such symmetry breaks are ubiquitous in Islamic art but also that they constitute a display of humility: no human production should attempt perfection since perfection belongs only to the Divine.
Figure 5. Two examples of Moroccan mosaics with approximate 4m symmetry, broken in both cases by slightly tilted cross-shaped features. The first picture was taken at the conference venue, the second at the Bahia Palace in the city centre of Marrakech.
In the eyes of a structural chemist
The human mind builds effortless connections between shapes that, even belonging to completely different contexts, share similarities of some kind. This fascinating correlation-making mechanism lies at the origin of a psychological phenomenon known as pareidolia: the tendency to associate a meaningful interpretation with an unrelated image, e.g. recognizing specific animals or faces in the shapes of clouds. When the brain creating these connections belongs to a structural chemist admiring Moroccan mosaics, the most obvious associations involve plenty of crystal structures. During my visit, I could recognize, in a split second, several materials even before focusing on the tiling structures themselves, simply due to spontaneous image association. The most evident were a polyhedral representation of a perovskite structure with marked octahedral tilting, the metal-organic framework MIL-53, and a simplified view of the covalent organic framework COF-366 (Fig. 6).
Figure 6. Three types of tessellations found at the Bahia Palace (above), and possible crystal structure interpretations (below) represented, from left to right, as a ball-and-stick model and with common graphical simplifications.
Similarities are not limited to crystal structures but sometimes also touch upon more general concepts in crystallography and solid-state chemistry. For example, the metric step mismatch of two meeting tessellations forcing the artist to cut them equally (Fig. 7, left-hand side) can be viewed as a 'grain boundary' in a sintered polycrystalline powder. A nonperiodic tilework containing layers of tiles with different colours reminds one of substitutional defects in a disordered crystal, where the same architectural role of different species allows for symmetry-equivalent sites to host different chemicals (Fig. 7, centre). Lastly, a 'core-shell' tiling (Fig. 7, right-hand side) resembles a nanoparticle composed of two different crystalline phases.
Figure 7. Mosaics evoking general crystallography concepts such as, from left to right, grain boundary, substitutional disorder, and core-shell structure.
Concluding thoughts
Any civilization, while expressing its artistic side, has developed its own style of pattern creation. One can simply look around the internet or better visit a foreign country with a different culture. Islamic tiling patterns are renowned, Moroccan Zellij mosaics arguably less so. Likewise, countless other forms of pattern-based art disseminated around the globe are hidden treasures waiting to be found, especially for crystallographers. It was about two years ago, during my visit to Melbourne for the 26th IUCr Congress, that I discovered the existence of beautiful aboriginal patterns by native Australian populations. Some time earlier, I discovered the elegant art of traditional Japanese decorative stitching, known as Hitomezashi, which I have since started entertaining myself with on paper.
There is something primordial about patterns that has trapped human minds at various stages of our history. I am convinced that it might relate to our ancestral fascination for crystals, which has even been observed in Homo Sapiens artifacts from more than 100,000 years ago (Wilkins et al., 2021), or even perhaps around 800,000 years ago (see https://www.iucr.org/news/newsletter/volume-29/number-2/ancient-crystal-collectors). No matter its origins or evolutionary relevance, this tendency keeps inviting me to search for new forms of pattern-based arts in human cultures, thereby adding more excitement and cultural depth to my journeys.
References
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