Mosaic has its own vocabulary, inherited from centuries of artisanal know-how. To help you better understand this art form and communicate more easily with mosaic artists, here is a glossary of the essential terms of the trade.
Materials
Tessera: the basic unit of any mosaic. This small fragment of material (glass, stone, ceramic) is assembled with others to form the design.
Glass paste (pâte de verre): glass colored throughout its mass, opaque or translucent, fired and then cut into tesserae. It is one of the most widely used materials in contemporary mosaic work, prized for the richness and depth of its colors.
Smalti: colored glass tesserae, traditionally opaque, cast and then cut by hand. Historically used in Byzantine mosaics, particularly for gold backgrounds.
Mosaic sheet (mesh-mounted sheet): a set of tesserae pre-mounted on a mesh backing or paper, making it easier to install over large surfaces.
Grout: a fine mortar applied between the tesserae after installation, to fill the gaps and stabilize the whole.
Mosaic adhesive: a specific glue, sometimes water-resistant, used to fix the tesserae to the surface before grouting.
Tools
Hammer (marteline): a small hammer used to cut tesserae by hand, a traditional technique inherited from Italian artisans.
Mosaic nippers (or “Japanese pliers”): a tool used to cut and shape glass or ceramic tesserae.
Notched trowel: a tool used to spread adhesive evenly on the surface, ensuring optimal bonding of the tesserae.
Grout float: used to apply grout between the tesserae and remove the excess before it dries.
Installation Methods
Direct method: the tesserae are glued one by one, or in sheets, directly onto the surface (wall, floor, furniture). This is the most common method for custom projects.
Indirect method: the design is first assembled face-down on a temporary backing (paper or mesh), then transferred and fixed onto the final surface. This technique is ideal for large compositions or complex designs, as it allows the artwork to be developed in the studio before final installation.
Opus Patterns: The Art of Arrangement
The term “opus,” from Latin, refers to the way tesserae are arranged in relation to one another. Each opus produces a different texture and visual effect.
Opus regulatum: arrangement in a regular grid, tesserae aligned in rows and columns. This is the simplest and most graphic arrangement.
Opus tessellatum: the tesserae are regular and aligned in horizontal rows, but offset from one row to the next, somewhat like a brick-laying pattern. Widely used in ancient mosaics, this arrangement works well for both geometric and figurative designs.
Opus vermiculatum: very small tesserae arranged in sinuous lines that follow the contours of the motif or subject (a face, a flower, an animal). The term comes from the Latin vermiculatum, evoking a “worm-like” arrangement. Widely used in antiquity for figurative scenes, this technique highlights the finer details of the design.
Opus palladianum: an irregular arrangement of tesserae of varying shapes, assembled to create a natural effect, close to raw stone or ancient paving. In contemporary mosaic vocabulary, it is sometimes likened to opus incertum, although the two terms are not always used as strict synonyms.
Behind every mosaic lies a precise vocabulary, the fruit of know-how passed down since antiquity. Knowing these terms means better understanding the technical and aesthetic choices that bring your project to life — and gaining even greater appreciation for the work of mosaic artisans.