GLOSSARY of TERMS
ADDITIVE and/or ADMIXTURE (or ADMIX)
An additive is a substance that is added to cement-based grout or mortar mix to increase and enhance its performance. (eg to make it more flexible, waterproof or frostproof).
An adhesive is a substance that bonds or sticks the tesserae to the surface or backing. Adhesives used in mosaic work include PVA glue (white craft glue), ready-mixed tile adhesive or cement-based adhesive, silicone sealant and epoxy glues. Specialized mosaic glues are also readily available.
Aggregate is the material that gives bulk to a mortar mix, which bonds together with the cement. the aggregate used in grout would typically be fine sand. Coarse sand gives mortar a more solid and stable base. Concrete contains a mix of aggregates, generally sand, gravel or other stones.
Andamento relates to the visual flow and direction within a mosaic produced by the placement of rows of tesserae.
The armature is the underlying structure and support of a sculpture, such as a metal framework to support concrete. However, wood, wire and plaster of Paris are also used.
The background refers to the area surrounding the main feature of a mosaic.
The backing is the base for a mosaic, and is what the tesserae are glued to.
Bozzetto is a small scale design created in preparation for a larger mosaic.
A cartoon is a full-sized drawing of a mosaic design. This can be drawn direction onto the area where the mosaic is going to be installed, or drawn onto paper, then transferred onto the surface. Cartoons can be enlarged from a smaller design.
Cement is a powdered material that sets by a chemical reaction with water. It is mixed with an aggregate such as gravel or sand to form an adhesive mortar or grout. Coarse aggregate such as gravel produces concrete. Water is added and blended with the dry mixtures to begin the ‘curing’ or setting process.
The term ceramic generally refers to the range of material created by firing clay at high temperatures. Within the context of mosaics, this would include ceramic tiles, terra cotta and pottery.
Ceramic tiles are made from thin layers of fired clay.
Concrete is a mixture of cement and aggregate (typically sand and various sized stones). When water is added to the dry mixture, a chemical reaction begins, causing the concrete to bind together the aggregates and cure or set.
CRAZING or CRACKLING
Crazing refers to a ‘crazy pavement’ effect in the glaze on a ceramic object caused by a pattern of cracks within the glaze. This can be accidental or deliberate during the firing stage, or may appear over time in aged items, and can resemble a mosaic.
Curing is the process of setting and hardening of a cement material such as grout or concrete. Curing is the chemical process of hydration, which requires water.
The Direct Method is a mosaic technique whereby the terresae are stuck directly to the surface or backing material. Once set and dry, the mosaic will be grouted.
Efflorescence is an effect on ceramic objects, particularly brickwork, caused by soluble salts seeping out of the brick and crystallizing on the surface.
Emblema is used predominantly in Roman mosaics that are finely detailed and often quite small. They are often pre-prepared prior, then inserted into a larger background area. The pural is ‘emblemata’.
Encaustic tiles are ceramic tiles made of a decoration of different coloured clays inlaid into their surface.
Epoxy is a very strong adhesive, two-part glue. It is useful for repair work.
Florentine mosaic refers to intricate inlay work from thin pieces of glass or coloured stone. The pieces are cut to fit together perfectly. This is also known as ‘pietre dure’.
Geometric pavement is a floor area covered with geometric tiles of two or more colours fitted together into patterns.
Glaze is a clay-based coating that becomes glass-like due to being fired at high temperatures. This adds colour and pattern to a tile or ceramic object and makes it more durable and waterproof.
The Grid Technique or ‘squaring up’, is a method for enlarging a small design into a full size ‘cartoons’ for a larger mosaic. It involves drawing up a grid of squares over the smaller picture or design. A similar grid of larger squares is drawn where the mosaic will go, and the design is copied, square by square, into the full-sized version.
Grout is a substance that fills the gaps between the tesserae in mosaics. One of the purposes of grout is to strengthen the object and make it more durable and long-lasting, by waterproofing and strengthening joints. Grout also has the effect of completing the design.
Grout is available ready-mixed (eg tile adhesive) and cement-based and is a dry powder that is mixed with water.
A grout file is a tool for breaking out loose or old grout from a mosaic piece (or tiling joint), in order for the grout to be repaired or replaced.
Grout sealer is a liquid sealant that is applied to a grouted mosaic to assist with waterproofing the grout. It also helps to protect the mosaic from stains and effects of exposure to the elements. For a cement-based grout, sealant is to be applied after the grout has completely cured.
INDIRECT METHOD (or the REVERSE METHOD or TECHNIQUE)
The indirect method is the technique of sticking mosaic tesserae to a temporary surface and then transferring them all together to the mosaic site. A typical method would be to glue the tesserae face down onto paper with a soluble glue (such as wallpaper paste). The paper is then reversed and pressed into an adhesive. Once set, the paper can be sponged off to reveal the tesserae.
The inlay technique involves pieces of stone, glass or wood of the same thickness, cut into precise shapes so that they fit together in a design without gaps, with the pieces set into a solid background. This effect is mosaic-like and uses the patterns of the materials to create realistic effects within pictures.
The intarsia technique involves pieces of wood or stone of the same thickness, precisely cut into shapes that fit together into a design without gaps. These are often set into a solid background.
Stone intarsia is often called ‘pietre dure’.
The interstice is the space between two tesserae. This is also called the ‘grout joint’.
The joint is the space between two tesserae, and is also called ‘interstice’.
A meta mosaic is a mosaic within a mosaic. This can also be the effect of using ‘crazing’ on pottery pieces in pique assiette work, or incorporating pseudo mosaic tiles.
In micro mosaics, ‘micro’ refers to the size of the pieces making up a complete picture.
A monogram is a group of letters combined into a single design or motif. These may be the initials of the artist (or client).
Mortar is a mixture of cement and fine aggregate (such as sand), to form a paste to be used as a grout or adhesive.
The term ‘opus’ refers to the ‘artwork’ as a way of describing the andamento or flow of the tesserae or other feature of mosaics.
Pelta is an ancient semi-circular shield shape that commonly features in Roman mosaics. Modified pelta shapes can interlock into a ‘tessellating’ pattern, for which contrasting colours may be used. The plural of ‘pelta’ is ‘peltae’.
Peppering is a way of adding additional colour to a plain background or large block of colour within a mosaic. Tesserae of other colours are placed throughout the main colour at particular intervals.
The term ‘Picassiete’ describes a style of mosaic that incorporates pieces of broken ceramics, such as dishes, cups, plates, tiles and other objects.
Pietre dure means ‘hard stone’ and is sometimes known as ‘Florentine mosaic’. It refers to intricate inlay work most often made from thin pieces of coloured stones. The pieces are cut to fit together perfectly, similar to ‘opus sectile’. These types of mosaic can look like a painting as the textured patterns of different types of stone are used to mimic features such as feathers, leaves, clouds and the like.
Pique assiette refers to the popular and versatile style of mosaic that incorporates pieces of broken ceramics of all kinds, shapes and colours.
PSEUDO MOSAIC TILES
Pseudo Mosaic tiles are ceramic tiles that have a pattern that creates the illusion of being a genuine mosaic.
PVA GLUE (POLY VINYL ACETATE)
Also known as white craft glue, PVA glue is a popular adhesive for use with the ‘direct method’ of mosaic creating.
PVA glue is water-based and does not contain solvents.
Diluted PVA glue (a solution of 3 – 10 parts of water to one part PVA) can also be used to prime a surface in readiness for applying tesserae.
The reverse method is also referred to as the ‘indirect method’. This technique involves sticking the tesserae to a temporary surface, then transferring them all together to the mosaic project.
A typical method is to stick the tesserae face-down onto brown paper with a soluble glue (such as wallpaper paste). The paper is then reversed and pressed into an adhesive. Once set, the paper is sponged off to reveal the faces of the tesserae.
Sgraffito refers to patterns or writing that has been scratched onto (or into) the surface of tiles or pottery prior to their being fired. The scratched marks reveal a different coloured clay beneath the glaze. This is also known as ‘graffito’.
Silicone sealant is a flexible and waterproof product that is used as a sealant for joints around plumbing fixtures (eg. sinks and baths).
Silicone sealant is an effective mosaic adhesive, particularly when both surfaces are not porous (eg. glass to glass). Silicone sealant can be used to secure tesserae to vertical surfaces due to its holding power.
Smalti are specialized mosaic tesserae made from richly coloured glass. The glass contains metal oxide which produces an almost infinite range of colours. The molten glass is poured into flat slabs which are then broken into individual smalti with irregular surfaces that may be pitted with air bubbles.
A squeegee is a tool for spreading grout. The spreader has a rubber blade on one edge, which helps to force the grout into all the spaces between the tesserae.
Subtrate is the backing or base for a mosaic project. This is what the tesserae are glued/stuck to.
Terra cotta is unglazed ceramic, generally red to orange in colour. Terra cotta is often used as a base for mosaic work, intended for outdoor use.
Terrazzo is a patterned floor surface made from polished stone chips set into a cement base or medium. This effect can look similar to marble or mosaic floor.
To ‘tessellate’ a surface is to cover it with shapes without leaving any gaps. In mosaic work, surfaces are often tessellated with irregular shapes fitted closely together.
Striking geometric pavements can be created from different tessellations of geometric and interlocking shapes.
Tesserae is the plural of ‘tessera’, which is the name given to pieces to be used in a mosaic.
A tile cutter is a tool specifically designed for cutting ceramic tiles and glass. A thin blade (usually a cutting wheel) is drawn across the surface of the tile, making a small, straight score mark into the glaze. Pressure is then applied evenly to either side of this line in order to snap the tile along the line. Both hand-held and bench-mounted versions are available.
Tile nippers are a hand-held tool used to break and snip mosaic materials such as crockery, china, tiles and glass.
Trompe L’oeil is a technique in mosaics and paintings that intends to trick the eye into believing that an object is real, rather than a picture. It relies upon the optical illusion caused by imitating perspective or other effects.
VITREOUS GLASS TILES
Vitreous glass tiles are thin, square tesserae pieces for mosaics. Often, one side is curved and ridged for better adhesion. Vitreous glass tiles offer a wide range of colours and are durable for outdoor use.