To the best of my knowledge, the first examples of Olmec concave iron-oxide-ore mirrors were discovered in the early 1940’s at La Venta, Tabasco, during the archaeological excavations directed by Matthew W. Stirling. The results of the three seasons of work have been described in a series of popular articles in the National Geographic Magazine by Stirling (1940a, 1943a) ad the Stirlings (1942), and in Smithsonian Institution Bureau of American Ethnology Bulletins 138 (Stirling 1943b), 153 (Drucker 1952), and 170 (Drucker et al. 1959). Although one small atypical magnetite mirror and a magnetite-mirror fragment were discovered in the 1942 season (Catalogue Nos. 3 and 4, respectively), the first complete mirror recognized as such as found during the 1943 season on the north arm of a cruciform cache of jade and serpentine celts (Drucker 1952). This find was designated offering 1943-E and the mirror is Number 5 in the present catalogue (Fig. 5). Later finds from the 1955 season, including the spectacular mirrors found in Offerings 9a and 11 (Catalogue Nos. 1 and 2, Figs. 1 and 2), are described in detail by Drucker, Heizer, and Squier (1959).

In the only previous real analysis (the four-page Appendix 3 of the latter publication), Gullberg (1959) presented optical and mineralogical analysis of the seven La Venta mirrors and fragments with a few speculations at to the technique of manufacture and purpose. Curtis (1959) showed that the mirrors are made of all three major iron-oxide ores: magnetite, hematite, and ilemenite. These are perhaps the ideal mineral substances to use for nontarnishing metallic-finish mirrors. Iron pyrites were apparently never used by the Olmec for concave mirrors. Pyrites are not fully oxidized minerals and tend to undergo almost total decomposition in an oxidizing environment. Most mirror backs now have little but a yellowish residue .that was once a highly reflective metallic-finish pyrite surface.