TURQUOISE TESSERAE OF MEXICAN MOSAICS


 Fig.1. Detail from a photograph from the British Museum

 Roberto Velázquez Cabrera
Virtual Research Institute Tlapitzcalzin
 Consultation document. First version, September 8, 2009. Latest version, September 22, 2009.

(Versión en Español)

INTRODUCTION

This brief report is the preliminary view of a native Mexican interested in a largely unknown lapidary technology from Ancient Mexico. The aim is to show how Mexican mosaics of tesserae (diminutive individual tiles in a mosaic) can be sawed, lapped and sanded. On August the 27th 2009, a conference of experiments in fine rock sawing (in Spanish)1 was presented during the IV Coloquio de Arqueología del INAH. We have posted here short videos (wmv) showing the main experimental procedures used in sawing rocks. The videos are posted without text or commentary to eliminate the translation problems. Here you can see pieces of rocks being cut with several manual tools such as:
  1. A ceramic saw with agglutinated abrasive;
  2. A thin and sharpened cane knife and wet abrasive (quartz) sand;
  3. Henequén (Agave fourcroydes o zodzqui in maya) cord and abrasive sand, and;
  4. A single fiber of agave and fine abrasive sand.
  5. A single fiber of Mexican agave can support more than 2 Kg of weight.
In this electronic document, the best method of producing the very small turquoise tesserae is presented; this document is aimed at individuals with an interest in the ancient lapidary technology of grinding rocks with manual tools and materials from nature and in experimental archaeology. Worldwide, the technology of flintknapping (such as making blades and arrow heads by hand) is well known and practiced by experimentation, but the ancient manual process of fine cutting and grinding precious rocks or gems is less known.

Several Mexican mosaics exist in museums and collections, for example, there are nine of the British Museum's collection. One of them was selected as the emblem of the special exhibition of "Moctezuma Aztec Ruler": a beautiful mask that is shown above in Fig.1. Those Mexican mosaics were published in a book along with their analysis (Stacey et al, 2006). It seems that the small tesserae were made individually, as noted in the "Construction of the mosaics" subchapter under "Mosaics under the microscope" (Ian Mursell sent to me the related copies of the book)3:

"The polishing marks left by the lapidary are remarkably clear when viewed under microscope (fig. 51). The grinding marks often lie in markedly different directions on adjacent tesserae, showing that they must have been ground smooth separately before they were set in place. Closer observation has also shown that some of the tesserae were carefully prepared with beveled edges - a feature noted in studies of turquoise working at sites such as Alta Vista. This enabled closer fitting of the tesserae over the curved surfaces of the objects." (Stacey et al, 2006, 38).

Unfortunately, the precise methods of sawing and sanding were lost five centuries ago, with the invasion and colonization of Mexico and very few rocks were found with traces of fine sawing4; I do not know if microscopic traces of sawing can be observed on the tesserae of Mexican mosaics, because usually they are lost with the process of lapping. Media information on the exhibition of the beautiful and unique Mexican mosaics does not include the potential methods of cutting and construction, which must be very difficult. Even now, with the technological advances of tools and materials that are used to work with rocks, a lapidary mosaic of similar quality has not been produced. Many small tesserae of turquoise and other Mexican mosaics were found on several archaeological expeditions, but their production methods were not published5: those recently recovered on Mount Tlaloc and a disc of turquoise with 15,000 tesserae found in the offering N0. 99 of the Aztec (Mexica) site Tenochtitlan. We do not known the construction method of any ancient Mexican mosaic and the Mexica lapidary work sites have not been found. It seems that the exact origin of the turquoise treasures of the Aztecs is unknown, but it has been proposed that:

"American Southwester mines produced most of the turquoise that adorned Mesoamerican's precious artifacts" (Harbottlle, 1992, 1).

 In another publication it was commented:

"Over the years, we analyzed more than 2,000 pieces of tuoquoise, about ten to 40 samples from each mine. Also, we examined nearly 100 artifacts from each of several mayor archaeological sites. Eventually, we traced several dozen pieces found in Mexico to specific mines over 1,000 miles away in New mexico, Arizona and Nevada." (Harbottle and Weigand, 1992, 56).

 Additional information on the ancient trade of turquoise is provided in another paper (Weigan and Harbottle, 1993, Chapter 6, 159-176)

There are other studies to chemically characterize turquois deposits, but the analyzed mines and ancient artifacts are from zones of U.S. (Hull, et al, 2007). In México, there are mines of turquoise, as some of the Northwester zone (Sonora, Durango and Zacatecas) and many ancient artifacts of turquoise, but similar studies on them are unknown.

Turquoise stones and turquoise products were tribute for the Aztecs from two ancient provinces Yoaltepec (now San Juan Ihualtepec, Oaxaca, Folio 40r of Codex Mendoza) and Tuchpa (now Tuxpan de Rodriguéz, Veracruz, Folio 52r of Mendoza Codex). The tribute from Yoaltepec were: "10 masks of turquoise" and "1 large packet of turquoise stones" (pictures from Mexicolore) (Berdan and Anawalt, 1992. 92). Tuchpa was requiered to pay to the Aztec empire: "1 string of turquoise stones and 2 round mosaic of small turquoise stones" (Berdan and Anawalt, 1992. 131).

I did not make copies of any of those beautiful Mexican mosaics, because it would require several years to produce with manual procedures; however, experimental lapidary manual work was done on the most difficult and basic tasks of their construction: the cutting and sanding of the very small tesserae, which is difficult, because some tesserae are very small (2 mm across). More than 200 smaller tesserae were found in a mosaic of a tarasca polished obsidian earspool of Michoacán, México (Pastrana, 2006, 52)6. I did not have access to ancient mosaics and electronic microscopes to analyze the surfaces of their teselas, but I had to learn and to practice the lapidary techniques to make experimental models of Mexican lithic resonators, such as the extraordinary and not well known Ancient Noise Generators (Velazquez 2006). The most important of them is the Ilmenita Sonora Olmeca (Velazquez, 2009), in part, because more than 150,000 similar multi-drilled pieces were found in the Olmec archaeological site of San Lorenzo Tenochtitlan and their ancient use is unknown. As a byproduct result of those experiments, it was possible to find and to test effective techniques to make manual fine cuttings of rocks.

SAWING A VERY SMALL ROCK OF TURQUOISE

A sharp crystal of quartz can be used to form a small channel (sgraffito or scratched) on the rock of turquoise to facilitate the initiation of the sawing. The hardness of quartz (7 in Mohs scale) is sufficient to cut turquoise rocks, because it is not very hard (5 – 6 Mohs). It is possible to use other crystals of greater hardness, but the quartz is not very difficult to obtain. According to my experiments, the best way of manually sawing a small rock with natural materials is using a sharp and thin knife made of cane7, otate8 or bamboo, with wet quartz sand9, as abrasive. The small rock must be sealed to a stick with a heated and melted vegetable resin or sealing wax to be able to be worked by a hand. It was informed that the sealing of Mexican mosaics could be made with resin (Stacey et al, 2006. 40, Fig. 54)10. Using this method is possible to produce straight cutting or sawing of less than one millimeter wide (Fig. 2), but this method of sawing a rocks is slow. A cutting of turquoise of 5 mm across was sawed in nearly 30 minutes of continuous work. If the knife is of metal, such as a thin lamina of copper, a similar cutting can be made in 15 minutes, but we do not know if copper was used as a knife at that time. Turquoise was highly valued and in short supply, so the fine sawing was necessary to minimize the loss of the rock, which typically occurred when a chisel was used. With fine sawing it is possible to produce thin slices of the rock to make small tesserae. The procedure is posted in another wmv video clip (Here you can see a piece of tesserae being cut by a thin knife of cane and quartz sand.


Fig.2. Sawing on turquoise of less than 1 mm wide.

SANDING A TESSERAE OF TURQUOISE

The flat surface of the sawing facilitates the process of lapping and sanding. This can be accomplished, if the tesserae are also sealed to a stick (Fig.3) and they are worked on a hard flat surface over wet sand of fine quartz or on a flat abrasive rock.


Fig.3. Photo of small sanded turquoise tesserae that were sealed to a stick.

The procedure of sanding is posted in another wmv video clip. Fig.4 shows the traces on the rock surface. Those traces are the "finger prints" of the abrasive that was used and how it was rasped or rubbed on the rock surface


Fig.4. Photomicrography11 of surface of the tesserae (5 mm across) of the video clip that shows the traces of the circular sanding with quartz.

Very small tesserae of sanded turquoise is shown in Fig. 5 with the microscopic traces of another method of sanding; straight movements, but in different directions.


Fig.4. Photomicrography of surface of one of the very small turquoise tesserae (1.5 mm across) that was rubbed on a sanding paper.

An interesting discovery was that the lapping and sanding can also be made on a flat surface of ceramic with agglutinated abrasive sand (Fig. 5).


Fig.5. Small turquoise tesserae (5 mm across) sanded on the surface of a flat piece of ceramic with quartz sand as abrasive.

This technique can be also used to polish the rock, if the flat surface is of leather or soft wood and a polishing agent, but it is not known if the ancient tesserae were polished, because the published photomicrographs show traces of the sanding (Stacey et al, 2006. 40, fig. 51).

Similar techniques can be applied to make tesserae from other types of rocks, such as those of ancient pyrite mirrors (Gallaga, 2009), but that rock is harder (6 – 6.5 Mohs)12. Many other small ancient lithic pieces such as the chalchihuites (blue and green worked hard rocks that were highly valued)13 could be sawed using similar methods, but the abrasive sand must be of the hardness of diamond (10 Mohs), corundum (9 Mohs), emery (7-9 Mohs) or topaz (8 Mohs) to be able to cut rocks such as jadeite (7 Mohs)(Langenscheidt, 2007, 202)14. The ancient exact methods of the lapidary work of jadeite and quartz also is a mystery to be explored with experimentation. This research program is very important, because there are many ancient objects of jadeite and other hard green rocks. Some of them are from the Maya culture, including beautiful mosaics with tesserae, such as the funerary mask of Pakal.

ADDITIONAL INFORMATION ON TURQUOISE MOSAICS.

The British Museum posted a programme of a conference on the Turquoise Mosaics. 11 - 13 December, 2009. It seems that the cutting and construction of turquoise tesseraes was not included in this programme.

CONCLUSIONS.

  1. The required quantity of time and quality of work that were necessary to make these turquoise mosaics masterpieces indicate that they were very highly valued. The reproduction of any of their tesseraes and their fine sealing and joining reveal and confirm this.

  2. If the ancient lapidary masters spent their lives, best efforts and technology to make the turquoise mosaics, at least, we must study them with the best available technology and the experimental methods to explore their manufacture as profoundly as possible .

  3. The experimental exercises of this brief report show that it is possible to test specific and effective methods of working a tesserae with manual tools and materials from nature. They also indicate that the process is very fine, delicate, precise and slow, but I can not estimate the total time used to make a masterpiece such as the mask15.

  4. In my opinion, every Mexican turquoise mosaic is more complex and of more value than has been recognized in the literature.

  5. Lapidary experiments can be used to analyze rocks that have not archaeological information or context and when a study of authenticity or genuineness is necessary16, and when a work of archaeological restoration is required.

NOTES.

  1. Experimentos finos de rocas preciosas. Una tecnología milenaria poco conocida y estudiada. IV Coloquio de Arqueología. Especialización en técnicas y enfoques recientes aplicados en la Arqueología. Museo del Templo Mayor y Dirección de Estudios Arqueológicos del Instituto Nacional de Antropología e Historia. 28 – 28 de agosto de 2009. México.
  2. The video clips were recorded in the Unidad Politécnica para la Educación Virtual del Intituto Politécnico Nacional.
  3. Ian Mursell sent me copies of four pages of the book with the information of the microscopic analysis. He has an educational web site on the Aztecs at Mexicolore. In México, does not exist a similar educational system on any mexican culture. His team has worked for 27 years. They have created a whole new section on Moctezuma and they added a page specifically on Turquoise Mosaics, which you can see here with an introcuction and a link to this electronic document.
  4. Some rocks with very fine sawings were found in La Ventilla, Teotihuacan (Gazzola, 2007, 62, Figs. 5 and 6) and in Montagua Valley, Guatemala (Rochette, 2006, 1, Figs 21 and 22), but their replication was not made. It seems that the method to study the ancient lapidary thechnology is a field of research work for the future. In the "Laboratory Analysis" section Rochette comments: "To date, no technological studies have attempted to detail the processes of jadeite artifact production used by the ancient Maya."
  5. Personal Communications of Victor Arrivalzaga, 2009.
  6. The small tesserae were glued in a mosaic disc inside the obsidian earspool. It is in the Museo Regional Michoacano.
  7. In México, the main available cane is the carrizo (Arundo donax o Phragmites commutis or acatl in the Mexican language nahuatl).
  8. Otate is otlatl in nahuatl (Guadua amplexifolia o Bambusa amplexifolia).
  9. In these experiments, I used quartz sand of mesh No. 100-110.
  10. It is commented that pine resin and copal were used to seal the tesserae of turquoise and it must be a very fine and delicate work of sealing, because they are fitted so artistically and perfectly jointed together that is impossible to detect their lines junction with the fingernails. The quality of the sealing with resin in very difficult to be replicated.
  11. Photomicrography is defined as photography through a compound microscope. The range of total magnification is usually from 10x to 1000x
  12. In three hours, 2 mm deep sawing was made in the rock of pyrite, with cooper lamina and quartz as abrasive.
  13. Chalchhihuites were found in many ancient offerings and ritual sites, including those of the highest mountains, as this small bead that was found in El Pecho of the Iztaccihuatl mountain at an altitude of 5220 m over the sea level. It is in a private collection of mexican alpinists with some extraordinay ritual small whistles that already were analyzed and posted.
  14. Unfortunately, hard abrasives have not been found in archaeological contexts. Langenscheidt commented me (2009) that kimberlite was fond in the North of Mexico and diamond could be obtained from other zones of America.
  15. I do not know the number of tesseraes of each turquoise mosaic, as those of the beautiful mask, that must have several thousands of finished and glued tesseraes.
  16. This study of the Crystal Skull is a good example, but the author recommended that the development of a public Atlas or Data Base of macroscopic and microscopic traces of rock cutting, sanding and polishing, with natural and industrial abrasives as well as mechanical and manual tools and methods is necessary.
BIBLIOGRAPHY

Berdan F. Frances. and Anawalt R. Patricia. 1992
The Codex Mendoza. University of California Press. Facsimile. V.2.

Gallaga, Emiliano 2009
La manufactura de los espejos de pirita: una experimentación. Conference presented in the Congreso Internacional de Americanistas. México City, July 2009.

Gazzola, Julie 2007
La producción de cuentas en piedras verdes en los talleres lapidarios de La ventilla Teotihuacan. Arqueología No. 36. INAH. México.

Harbottle, Garman 1992
The Turquoise Trail: Chemical Analysis at BNL Supports Controversial Theory. Brookhaven National Laboratory. Vo;. 46 - No. 6.

Harbottle, Garman and Weigand C. Phil 1992
Turquoise in Pre-Columbian America. Scientific America.

Hull S., Fayec M., Mathien F.J., Shelley P. and Durand R.k. 2007
A new approach to determining the geological provenance of turquoise artifacts using hydrogen and cooper stable isotopes. Journal of Archaeological Science. V. 35, I. 5, 1355-1369.

Langenscheid, Adolphus 2007
Lapidaria mesoamericana, una reflexión sobre los abrasivos posiblemente usados para trabajar los chalchihites duros. Arqueología. No 36. INAH. México.

Pastrana, Alejandro 2006
La obsidiana en Mesoamérica. Arqueología Mexicana. Vol. HIV, No. 80.

Rochette, Erick 2006
Investigating Jade Prestige Goods Production, Middle Montagua Valley, Guatemala. FAMSI website. Pdf report 05069.

Stacey, R. Mc Eswan, C. Middleton, A and Cartwright, Caroline C. 2006
Turquoise mosaics from Mexico. The British Museum Press, London.

Velázquez Cabrera, Roberto 2006.
Ancient Noise Generators. 4th Symposium of the International Study Group on Music Archaeology at Monastery Michaelstein, 19-26 September 2004. Studien zur Musikarchäologie V, Orient-Archäologie 20. Rahden/Westf.

Velázquez Cabrera, Roberto 2009.
Generador de Ruido Bucal de Ilmenita. Arqueología. INAH. No. 40. México..

Weigan C. Phil and Harbottle Garman 1993.
The Role of Turquoises in the Ancient Mesoamerican Trade Structure. Chapter 6 of The American Southwest and Mesoamerica: system of prehistoric exchange, by Jonathon E. Erickson and Timothy G. Baugh.