The consequence of working that way is that no two panels are identical, not even inside the same building. And it explains why zellij looks so different from any industrial tile even when the pattern is similar.
It is a craft of subtraction, not decoration. What you see is not added on top of a surface: it is the surface, broken up and put back together.
01 It is cut, not painted
The starting point is a square clay tile glazed in a single colour, with no pattern at all. Every shape comes out of it: stars, spindles, triangles, crosses, long straps and tiny filler pieces, each with its own name in the workshop.
The cutting is done with a tool that looks like a small heavy axe with a wide blade. The craftsman rests the tile on a stone edge and pares the outline away with short blows, turning the piece in his hand, until it matches the template.
The bevel that results is part of the system. The edge does not come out straight but slightly angled inwards, which locks the pieces into the mortar and keeps the visible joints extremely fine.
No two panels are alike because no two pieces are alike. Each one was made by striking it.
02 It is assembled back to front
Here is the part hardest to believe. The panel is not composed looking at it: it is composed face down, with the glazed side against the floor, so that throughout the work the craftsman only sees the clay backs.
Once the composition is closed, mortar or plaster is poured over the back and left to set. The resulting slab is lifted, turned over, and only then does the pattern appear, having existed until that moment only in the head of whoever laid it.
That method forces you to work in mirror image and to memorise the position of every colour. It is also the practical reason panels are made in square or rectangular modules: they have to be liftable.
03 The clay decides where it is made
Fez is still the country's production centre, and the reason is not prestige but geology. The area has Miocene grey clay composed mostly of kaolinite, with a calcite share of around 16 per cent.
That mix matters because it determines how the piece behaves. Too soft a body crumbles when struck and too hard a one splits where it should not; the local clay takes the cut without splintering and holds the glaze without crazing it.
That is why the craft has not moved. The workshops of Meknes, Salé or Marrakesh work in the same style and follow Fez's lead, but the raw material everything starts from comes out of the hills around this city.
04 Azulejo and alicatado
The Spanish and Portuguese word azulejo comes directly from zillīj, the Arabic name of this technique. It has nothing to do with the Spanish word for blue, though it looks as if it might: it describes the smooth, glazed surface of the piece.
The other Spanish term says it even more plainly. Alicatado derives from the Arabic verb meaning to cut, and it is the name given in Spain to this same mosaic of chiselled pieces, the one in the great Granada ensembles.
There the craft was pushed to its limit: in some Alhambra compositions there are pieces barely two millimetres wide. It is worth keeping in mind as you cross a courtyard here, because the two traditions are one technique with centuries of traffic both ways.
05 Why the pattern never quite repeats
The composition starts from regular polygons and the tessellations they allow. Out of that come the eight-, twelve- and sixteen-pointed stars, and the white straps that lock them together and which, if you follow them with your eye, almost never end where you expect.
Those patterns caught the attention of mathematicians and of artists too: the tessellations of this tradition were a direct source for Escher's work, which he studied on the spot in the Alhambra.
The palette has rules of its own too. While blues and turquoises dominated in the Islamic east, in the west yellow, green, black and light brown took over, with blues and turquoises in the mix and almost always on a white ground.
06 What to look for
First, the size of the pieces. The smaller and more numerous they are, the more work and usually the older the school; modern imitation panels solve the same pattern with painted square tiles and give themselves away at once.
Second, the edges. Go close to a joint and see whether the line between two colours is a cut or a painted stroke. That detail tells a real mosaic from a reproduction in three seconds.
And third, where it is placed. Zellij is used almost always from shoulder height down, in dados, floors, fountains and benches, because that is the part that gets touched, wetted and scrubbed. Above, it gives way to wood and plaster. The decoration is also an answer to wear.
