Mosaic Tiles

Email: mosaics(at)susan(dot)drakkar(dot)org

Mosaic is an art decorating technique using small shards of colored stones/pebbles, clay, brick, glass or other material. 1) The small pieces, known as tesserae2), are put together using mortar 3) to form essentially a permanent painting made from stone. Mosaics are an art form which has been around since about 3000 BC. The earliest examples were made by the Sumarians 4) in Ancient Mesopotamia. 5)6) Mosaics made from pieces of black stone, red marble and mother of pearl adorned stone sculptures of animals. These were embedded in a black colored mortar. They decorated harps, goblets and board games, among other items, with mother of pearl and lapis lazuli mosaics. 7) They also decorated columns using cone shaped pieces of colored clay. Later in the eighth to the fourth centuries B.C., mosaic floors made from river and sea pebbles were found. Mosaics spread into Itlay during the Hellenistic 8) period, probably from Greece. The best Roman 9) mosaics come from Pompeii 10) and Herculaneum11).12) By the first century A.D. mosaics can be found in Pompeii, depicting everyday life. Black and white tesserae were popular color motifs.13)

Mosaics became very popular in Roman buildings, houses and shops. Roman mosaics were found on floors as well as walls. The best rooms of the house would have been decorated with the mosaics. They were usually found on the dining room floors, but bathrooms were also adorned.14) Roman nobles started to fund mosaic projects in various churches. Marble tile inlaid floors in geometric patterns started to be executed. Mosaic panels depicting religious images, done in the Hellenistic style, adorn the Church of Santa Maria Maggiore in Rome built about 352-366 A.D.15) At this time mosaic factories were set up in the large cities. It is believed that the more intricate panels were created in a workshop by the master mosaic artists and installed and filled in, by the apprentices.16)

In 77 AD., Pliny the Elder17) describes in his book,”Naturalis Historia”, the process of making a mosaic floor. He tells of three preparatory layers before the mosaics are laid. The “Statumen” is “tightly packed pebbles and rocks between three and five inches thick.” The “Rudus”, is “three parts gravel, and fragments of terracotta and one part lime.” This layer is essentially a “rough mortar” about 10 inches thick. The “Nucleus” layer is again three to five inches and is comprised of “three parts sand, mixed with smashed tiles and bricks and one part lime.” This layer is a finer grade mortar than the “Rudus” layer.18)

Roman architect Marcus Vitruvius Pollio described in his book “De Architectura” the process of making a mosaic bathroom floor in the middle of the 3rd century A.D. Vitruvius, as he is known, wrote ten books detailing architecture in that time. In his book he references Pliny and the three preparatory layers. He refers to the first layer is called “Statumen”, which is a layer of fine rubble. The one above that is called “Rudus”, which is well-compacted mortar not less than three-quarters of a foot thick. Next is the “Nucleus”, a layer of mortar mixed with terracotta aggregate not less than six inches thick. The tesserae for the mosacis was then placed on top. 19) Ultimately this practice of layering was abandoned either partially or completely, as archaeological evidence has shown. The reason it was abandoned was probably due to the enormous time factor involved in execution of the mosaics.

The tesserae used in the Roman times included; stone, several colors of brick, colored glass, fired clay, yellow and red sandstones, ironstones, slate and samian 20) pottery.21)22) After the layers are set to receive the tesserae, drawings or guide lines were scribed into the top layer. Roman mosaics depicted everyday life, with different foods, flowers, people and wildlife, including fish. There were also lively examples, including pictorial hunts, theatrical and circus representations, mythological creatures,and various Roman Gods.23)

After the decline of the Roman Empire, The Byzantine Empire 24) continued the mosaic tradition. In the fifth century a wealthy Vandal 25) landowner commissioned mosaic pavements in Carthage.26) These mosaics depicted a horseman in front of a building and the other a bear rubbing a tree.27) Byzantine mosaics in the sixth through the eight century still depicted everyday life; people, flowers, animals, etc. The sixth century was also the time when the grand mosaics in the Church of San Vitale at Ravenna 28) were made.29) The trend in mosaics had now turned to religious motifs and flourished from the sixth to the 15th centuries.

The mosaics were placed in the churches to tell the story of Christianity to those who could not read. They also were meant to inspire reverence and meditation. Individual mosaics were placed in order of precedence. Portrayals of Christ were at the highest points, next would be, the Angels, and scenes of the major events in Christ’s life. Then in descending order, the Apostles, the Prophets and lastly the Saints. 30) Mosaics were even ordained by the church as to the measurements of the mosaics and the style in which they should be executed. One of these traditions states that “a man measures nine heads”, “that his hairline rise a nose’s length above his forehead; and that if the man is naked, four nose’s lengths are needed for half his width.” 31) Byzantine mosaic traditions spilled over into Russian churches. Mosaics made to look like icons 32) began to appear in the eleventh century Kievian 33) churches.

Glass 34) tesserea was being used more during the Byzantine period. The artists at Alexandria discovered that the glass could be set at an angle to catch and refract light. Colored, opaque glass paste or smalti 35) became popular. The clear glass could also be coated with gold and silver dust along with other colors.36) Theophilus37) writes about how to make the gilded glass cubes, in his book “De diversis artibus,” in 1125 A.D. 38) He says to “make glass sheets the same way that windows are made out of clear white glass, a finger thick.” “split them with a hot iron into tiny squares and cover them on one side with gold leaf...”,”...Cover them with clear ground glass,.... and lime or ashes, and fire them in the window-glass kiln.”39) The “Mappae Clavicula”, written in 1170 A.D., also describes how to gild the glass for mosaics. The process is similar, but a description of how to polish the glass to bring out the color is added. 40) Giorgio Vasari (1511-1574),41) in his book, “Vasari on Technique,” tells us to use gum-water to adhere the gold leaf.42)

The mortar used to adhere the tesserae is a lime and sand mixture. In the third century, Vitruvius writes in his second book, in “De Architectura”, describing the process of making mortar. “Lime which is burnt either from whitestone or flint”, “When slaked for making mortar, if pit sand be used, three parts of sand are mixed with one of lime.” “If river or sea sand, two parts of sand to one of lime.” 43) He goes into detail the properties of lime and how it should be prepared for use in mortar. The “Mappae Clavicula”, also gives us a description of making mortar. It goes into detail how to find the right kind of sand and lime to use. It tells us to mix two parts of sand, one of lime, if using river sand add a third part crushed chalky brick. 44) Giorgio Vasari, in “Vasari on Technique”, believes that the mortar,(he calls it stucco) used in the ancient pavement mosaics was made from lime and marble dust. The recipe for stucco that Vasari uses is made of travertine, lime, pounded brick, gum-tragacanth 45) and white of egg. Once it is made it is kept wet with damp cloths for two to four days, depending on the weather. 46) Louisa Maclehose, translator of the “Vasari on Technique”, suggests that every mosaicist had their own recipes for making their mortar. 47)

To build the images, Vasari tells us to trace a “cartoon” drawing, with or without color, onto the wet stucco wall, one section at a time. The tesserae is then set into the stucco.48) Ancient Romans used a similar method, drawing on the prepared surface before applying the mortar and tesserae.

Throughout history, there were three methods in which to place the tesserae. The first is the “Direct Method”, done by placing the tesserae directly into the wet mortar. A wooden board is then used to level the pieces to create a smooth surface. 49) The next method is the “Indirect Method”, laying the tesserae upside down on a cloth and then applying the mortar to the back of the tesserae. After the mortar is applied the design is placed on the wall or floor and the cloth removed when the mortar has dried. In this method the drawing would be on the cloth. 50) It is believed that the Romans applied this technique also. The skilled artisans designed the roundels and had them put in place, with the apprentices doing the background fillers. 51) Louisa Maclehose translator of Vasari’s book suggests a method using a gum covered cloth to adhere the tesserae. The tesserae is then covered with the mortar, directly installed. After the design is in place and the mortar dried, the cloth is removed by wetting. 52) The third technique is referred to as “Double Reverse Method.”53) This method was used by the artists in Ravenna. A reverse “cartoon” drawing is traced into a lime bed and the tesserae is placed directly into the lime. When the mosaic is completed a cloth is placed over top using a water based glue, traditional rabbit skin glue. When the tesserae has adhered to the cloth, the mosaic is removed from the lime base and the lime cleaned off the back. This is then applied to the final surface just as in the “Indirect Method.”

There are several design methods used to lay the tesserae, the first three are the most common used:

1. Opus Tesselatum: Black and white cubed tesserae ranging in size from 3/16th to 1 1/8th inch, placed in a geometric pattern.54)55)
2. Opus Sectile: A paving technique, using larger slabs to form geometric shapes and other designs. 56)57)
3. Opus Vermiculatum: Very small tesserae under 3/16th inch cut to exacting shape and laid close together. These form an outline around the form.58) In some cases only one row of outlines were used sometimes you see two to three rows surrounding the form. The outline defines the form better.59)
4. Opus Incertum: Irregular shapes fitted together in a random fashion.60)61)
5. Opus Lapili: Pebble mosaics bonded with compacted earth or a mixture of sand and lime.62)63)
6. Opus Musivum: Wall mosaic where only glass paste64) tesserae, (smalti) are used.65)66)
7. Opus Quadratum: Cube shaped tesserae placed in horizontal rows to form a checker board pattern.67) 68)
8. Opus Reticulatum: This is the same as the opus quadratum, with the pieces positioned on the diagonal, so the rows form diamond shapes instead of squares. 69)70)
9. Opus Segmentatum: Mix of small and large tesserae of the same color used to create geometric designs.71)
10. Opus Scutulatum: Tesserrae in diamond shapes arranged tightly.72)73)
11. Opus Spicatum: Tesserea or pebbles arranged in herrringbone pattern.74)75)
12. Opus Signinum: Tesserea placed with space between them in a geometric pattern.76)77)
13. Opus Circumactum: Laying tesserae in a fan-like pattern, usually used as a background.78)
14. Opus Classicum: Combination of opus tesselatum in the background and opus vermiculatum surrounding the main figure.79)

The traditional tools used to cut the tesserae are called a hammer (martellina) and a hardie. The hardie is a sharp cutting wedge set into a tree stump. A link to a “you tube” site showing the use of the hammer and hardie is here at this footnote:80) On this site there are hammers and hardies for purchase. A picture is available in the Joaquim Chavarria’s book as well.81) The large tesserae is placed over the hardie at an angle and the hammer is slammed down on top of the tesserae, resulting in the breakage of the tesserae. This can be done in a fairly controlled manner. Glass tesserae was cut using a hot iron, according to Theophilus in the 1125.82) A file was also used to further refine the pieces. Traditional glues include rabbit skin glue, bees wax, and gum arabic (used on the cloth for the indirect and double reverse methods). Micro mosaics were done entirely with wax, no mortar is used.

We have available a wide variety of modern tools to expedite the process of making mosaics. The hammer and hardie are available, which is very easy to use with a bit of practice. Motorized wet tile cutters work too, as well as tile and glass nippers in a variety of sizes. Glass, ceramic,and stone tesserae can be obtained already cut. The list of adhesives to glue down the pieces and grout to seal the pieces are a mile long. Modern parafin wax can be used to adhere your tiles before grouting. Any glue that says “tile adhesive” or “tile mastic” will work. White carpenters glue and neoprene glue can be used.83) Grouts come in sanded and unsanded varieties. If using wide grout lines it is better to use the sanded grout. There is an epoxy grout which should be used on kitchen counters. Make sure to check the labels of your glues and grout and match them to your particular project. Ask yourself if the mosaic will be exposed to the elements, freezing and thawing, high moisture area like; bathroom or kitchen counter, etc, etc,and pick the most appropriate. The closest traditional recipe for mortar is a recipe given to me by a traditional mosaic artist. He uses a 50/50 mixture of “1A Portland Cement” and “washed silica sand” or “mortar sand”. He warns not to get sand out of bulk bins to get them in bags only. Mix this with water to the consistency of a thick sour cream. If you want to color the mortar use the “white 1A Portland Cement” as a base to add colorants. Do not use a waterproof cement. In his class he taught us to wipe the extra mortar out when you leave your work and not to let it dry up, as the mortar will be hard to remove if not. A variety of bases can be used also. They include; laminated wood, cement fiberboard, slabs of marble, stone, terra-cotta tiles (Or any unglazed tile or pottery).84)