MOSAIC GLOSSARY – DEFINITION OF TERMS

This page isĀ  a combination of Glossary and Mini-Encyclopaedia. It is your reference for finding definitions of Mosaic Terms. It is never complete, but will be updated regularly.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

A

Adhesives:The tesserae may be permanently attached to the surface of the article or structure being decorated with a large choice of modern glues or adhesives. The selection of adhesive would depend on several factors, such as the function of the mosaic; the combination of materials being used; the porosity of the mating surfaces and the degree of exposure to the elements or the amount of wear and tear that is anticipated. Traditionally mosaics were simply bedded in cement paste or mortar and this is still the medium for major works. However, today all tile shops supply ready-mixed cement-based bedding adhesives, that are modified with polymers to make them easier to spread and improve the adhesion to the tiles and backer material. Cement-based adhesives are suitable for adhering tesserae to rigid surfaces, such as walls or floors. PVA (Polyvinyl acetate) adhesive is useful for sticking the mosaic tiles to most other surfaces, unless they are exposed to moisture or frost. EVA (Ethylene vinyl acetate) glues may be substituted where some moisture is anticipated, but this is still not recommended for outdoors, where an Epoxy resin would be more suitable. For adhering to impervious or very smooth materials such as glass flexible silicone adhesives are commonly the glue of choice.

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Andamento:
A term that describes the general way that the tesserae are organised in rows or “strings” to give a sense of overall flow or direction.

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B

Backing:
The permanent backing is the firm surface that is to have the mosaic work applied to it. A temporary backer is used in indirect mosaics, and may be of craft paper, which is attached to the tesserae with a water soluble craft glue that can later be washed off. Commercial vitreous or ceramic tiles for use in showers or swimming pool surfaces are usually supplied in small sheets with a sacrificial backer of an open weave fibre mesh.

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C

Ceramic:
(See also Ceramic Tiles). Ceramic material is made by firing clay and other minerals at very high temperatures to produce pottery of various types. The term ceramic is a generic term that encompasses such material as porcelain, china, terracota, and earthenware. Ceramic ware may be glazed or unglazed, decorated or plain and porous or impervious.

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D

Direct Method:
In this type of mosaic construction the tesserae are stuck directly onto the backing surface using an adhesive glue or bedding material such as cement mortar. This technique is especially suitable, where the exposed surface of the tesserae need not be entirely flat, such as on wall decoration.

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E

Epoxy Resin:
An exceptionally tough adhesive or bedding material that is activated by mixing two component resins together, just prior to use. The resins combine in a chemical reaction to form a new compound that sets very hard and provides an incredibly strong and durable adhesive bond to the tesserae.

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F

Floor Mosaics:
The Romans made the practice of decorating floors with mosaic tiles their own distinctive artform. This technique provided them with easy to clean, waterproof surfaces that could be used to bring light and grace into their homes and public buildings – especially to their famous baths. They were fond of depicting heroic scenes from mythology on their floors and of exciting activities such as chariot racing, but also enjoyed homely portrayals of food and livestock – all fashioned with great exuberance and care. They paid careful attention to borders and often extended geometric patterns over large areas of floor. Byzantine churches, medieval cathedrals and Moorish palaces took up this tradition and produced wonderful tile work on their floors, which have stood the test of time.

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G

Glue:See Adhesives.

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GOG Mosaics:Glass on glass (GOG) mosaics are created by glueing fragments of coloured glass onto a clear glass pane, using a colorless adhesive, such as silicone. A formal stained glass effect is achieved by grouting the joints between the colored pieces with a dark grout.

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Grout:
The interstices between the mosaic tiles (tesserae) are usually grouted. This is a filler material, usually cementitious, that adds strength and durability to the mosaic piece, by locking the tesserae together in a firm matrrix. The grouting is especially important for mosaic work in wet conditions or when exposed to extremes of weather, particularly frost. The grout is not a visually neutral element of the piece, but is usually done in such a way as to enhance the visual impact of the medium. The grout may well be tinted with oxides or other stains to increase the definition. Cement grouts may be coloured by mixing in acrylic paint. Commercial tlle grouts are easier to use and are readily available in neutral and tinted packs and may be rendered waterproof by the addition of proprietory additives at time of mixing, or the grout may be sealed after it has hardened. Some mosaics are left ungrouted, especially where the colors of the tiles are needed to “flow” together to create a more homogenous effect.

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H

Halving:
Square tesserae are often cut into halves to produce rectangular pieces, often used for border designs and in set pieces for setting up a bonded brick or herringbone pattern.

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Hammer and Hardie:
A traditional arrangement for cutting, or squaring off tesserae. The hardie consists of an upturned masonry (cold) chisel firmly embeded in a substantial block of wood, with its cutting edge uppermost. . The mosaic tile to be cut is pressed down across the edge of the hardie and given a sharp tap with a flat-edged chipping hammer (like a geologist or miner’s hammer).

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Hardie:
The hardie consists of an upturned masonry (cold) chisel, firmly embeded in a substantial block of wood, with its cutting edge uppermost. (see Hammer and Hardie)

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I

Interstice:
The Interstice is the gap or space between tesserae, which is usually filled up with grout. The width of the interstice may be wider or narrower, depending on the desired effect, but it is usual to try to keep the width fairly constant for each seperate mosaic piece. Intestices are never left open, where the piece is needed to be waterproof or is subject to wear and tear, such as on a trafficked floor. Of cours the interstices should never be left ungrouted, where the mosaic could be exposed to frost, as the expansion of ice would quickly loosen the tesserae.

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J

Joint:See Interstice.

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K

Kit:
Mosaic kits are sold commercially and on line through Amazon and are excellent gifts for a beginner or a for an artistic child. They usually arrive complete with all you need to make a simple mosaic set piece, including adhesives, colorful tesserae blocks, grout and a backer board, with an embossed pattern for easy construction.

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L

Lapis Lazuli:
A deep blue semi-precious stone from Afghanistan used in some ancient mosaic works.

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M

Mosaic:
The term mosaic actually refers to an artistic effect rather than to a specific technique or the use of any particular medium. A mosaic effect is an arrangement of shaped pieces laid out with matrix of uniform colour in between, seperating the individual pieces. Generally the term is reserved for small ceramic, stone or glass blocks (tesserae) fixed with adhesive or cement in patterns onto a backing surface, with the interstices between blocks filled up with grout. (See also photo mosaics).

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N

Nips or Nippers:
Mosaic nippers are essentially tile nippers, as used by tilers and are used for cutting or shaping tiles or tessarae into desired sizes or shapes. Unlike carpenter’s nips, the teeth of the nips never actually come together when the handles are depressed – a gap of about an eighth of an inch remains, which uneven prevents shattering of the block or tile being cut. Nips can be used to round the edges of the mosaic pieces, by gradual nibbling them into shape

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O

Opus:
Opus is the Latin word for work. The Romans defined various styles of mosaic work, specifically pertaining to the arrangement of the rows of tesserae, with the prefix opus, such as “opus regulatum” and “opus vermiculatum” – these terms are still very much in use today.

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Opus musivum:
Opus musivum is an expansion of the single outlining band of Opis vermiculatum by wrapping additional ” nesting” bands of tesserae around the initial band, to fill up all the surrounding space around an object . This gives the impression of emphasis and movement to the object or figure.

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Opus palladanium:
Opus palladanium is an arrangement of irregular shaped tesserae to give a “crazy-paving” effect. The one stipulation is that the grouted interstices between the tiles should be a constant width.

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Opus regulatum:
This is a regular pattern of square tesserae laid out in rectangular rows as in courses on a brick wall. It is used to fill expanses of bacground or borders and is very static..

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Opus sectile:
This is a technique where larger tile pieces are cut to specific shapes to fit into each element or object within a picture, it is similar to a puzzle, or to leaded stained glass in churches..

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Opus tesselatum:
This technique is similar to Opus regulatum, using square tesserae, but more emphasis is given to ensuring that the tesserae are laid out in a true rectilinear fashion with rows and columns in line , as in a checkerboard. It is used for geometric patterns and borders, rather than as a general filler for backgrounds.

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Opus vermiculatum:
This technique derives its name from the Latin word for worm – vermi. A single row of even sized tesserae is applied in a band around the main images or figures, like a halo, to give them emphasis and feeling of movement..

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P

Pelta Style:
A series of repeated patterns where the tesserae are arched in part circles to form the appearance of interlocking shield shapes. This ancient Roman style is still very popular for modern driveway brick paving. It derived its name from the greek word “pelta” for a light shield (light troops were called “peltasts”).

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Q

Quartering:
Square tesserae are often cut into quarters to produce smaller square pieces, often used to offset border designs and for closures.

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R

Reverse Method:
See “Indirect Method”.

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S

Smalti:
Smalti are glass tiles that are still hand-made by a traditional process and are only made in Venice (Italy). They come in a huge range of brilliant colours. The individual tesserae blocks are usually 20mm x 10mm (3/4 x 3/8 inch). Smalti are formed from melted glass that is poured into sheets and cut to size into individual blocks. The molten glass is combined with minerals to give exceptional brilliance and sparkle. Because of the way they are formed and cut, the tesserae blocks are slightly irregular in size and shape, so when set into a mosaic piece, the varying surface angles of the individual blocks reflect light in different ways, giving sparkle and “life” to the work. Byzantine mosaics on religious themes at Ravenna and Constantinople (Istambul) are glorious examples of Smalti used to its best effect. Smalti cubes may also include silver or gold leaf, within the body of the tesserae – but these are extremely expensive.

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T

Tesserae:
Tesserae (singular tessera) are the small blocks or tiles used in mosaic work. In ancient times they would be cube shaped and made from natural stone, marble or glass. Modern tesserae are made from a variety of materials, of which viteous glass is used most frequently. The pieces may be up to 20mm square (3/4 x3/4 inch) and 5 to 10mm (1/4 to 1/2 inch) thick, but smaller sizes are common.

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Tiles:
The small tile pieces used in mosaics are called by the Latin word “tesserae” (single = tessera). Tesserae were originally formed from natural stone or marble, but may be made of vitreous glass, ceramic material, “smalti” , semi precious stone, metals and many other materials. Larger tiles are sometimes also used in mosaic combinations – especially where the scale of the work is large.

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U

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V

Vitreous Glass:
These opaque glass tiles are made from melted glass paste, which is cast in moulds. They have one side smooth and the back of the tile is ridged for better glue adhesion. These tiles are very durable and are used commercially for swimming pools and shower linings etc. The usual tile size is around 20 x 20 mm (3/4 x 3/4 inches) and the tiles are usually supplied on temporary backer sheets of around 300mm x 300mm (12 x 12 inches).They come in a range of about 80 colors.

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W

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X

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Y

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Z

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