very intriguing and I'm sure continues to have affect today within the social consciousness of the Mexican people as well as those who live in close proximity to Mexico and other areas colonized/occupied by Spain. Here is a bit of information regarding how the many "levels" of the caste system were codified in the 18th century through art:
The production of casta paintings spans the entire eighteenth century. These works portray the complex process of mestizaje or race mixing among the three major groups that inhabited the colony: Indian, Spanish, and Black. Most of these paintings are comprised of sixteen scenes depicted on separate canvases, although occasionally the scenes are represented on a single, compartmentalized surface (painting 1).2 Each scene portrays a man and woman of different races with one or two of their progeny and is accompanied by an inscription that identifies the racial mix depicted. The series follow a specific taxonomic progression: at the beginning are scenes portraying figures of "pure" race (that is, Spaniards), lavishly attired or engaged in occupations that indicate their higher status. As the family groups become more racially mixed, their social status diminishes. In addition to presenting a typology of human races and their occupations, casta paintings also include a rich classificatory system within which objects, food products, flora, and fauna are clearly positioned and labeled.
Since the sixteenth century, Spaniards had transposed their own social schema onto their colonies in the New World. The subordination of State to Church and the ideology of limpieza de sangre (purity of blood)--where the absence of Jewish or Muslim blood defined an honorable Old Christian--were factors contributing to Spain's hierarchically organized society, whose members had clearly delineated social roles.4 When the Spanish colonized the New World, they brought with them this division of society into nobles and plebeians. By converting the Indians to the Christian faith, an imperative that gave justification to the colonial enterprise, Spaniards became the aristocracy of Mexico regardless of their origins or occupations. The supremacy of Spaniards (or whites) was remarked at the end of the colonial period by Alexander von Humboldt (1769 - 1859), a German natural scientist who traveled in the New World: "any white person, although he rides his horse barefoot, imagines himself to be of the nobility of the country."5 Indians, who, with the exception of their own nobility, were associated with agriculture, became the tribute-paying plebeians. Nevertheless, the Spanish system admitted the existence of an Indian Republic within the colony, which meant that the Spaniards recognized the existence of an internal hierarchy for Indian society. Because Indians were destined collectively to become "New Christians," they merited the protection of the Spanish Crown. Blacks, on the other hand, were brought to the New World as slaves and were in theory situated at the lowest echelons of society; they worked as domestic servants for the Spaniards and as laborers on the sugar plantations, mines, and estates. Blacks were considered a homogeneous group with no rights and were redeemable only on an individual level, once they had proven their loyalty to the Church and their masters.6 In practice, however, Spaniards often preferred Blacks to Indians and employed them to oversee Indian labor. By their association with whites, many Blacks came to occupy a de facto position superior to that of Indians.
While intermarriage among the three groups did not become common until the second half of the seventeenth century, sexual contact among Spaniards, Indians, and Blacks occurred as early as the sixteenth century.7 This resulted in the growth of a large group of racially-mixed people known collectively as castas-the general term used by Spaniards and creoles (Spaniards born in the Americas) to distinguish themselves from the large masses of racially-mixed people. By the end of the eighteenth century, approximately one quarter (25.4 percent) of the total population of Mexico was racially mixed.8 From the sixteenth century on a variety of names served to designate the different castas of Mexico. The most widely used terms were those referring to the mixtures between the three main groups: mestizo (Spanish-Indian), mulatto (Spanish-Black), and zambo or zambaigo (Black-Indian). In the seventeenth century two additional terms appeared: castizo (a light-skinned mestizo) and morisco (a light-skinned mulatto).9 By the eighteenth century a whole array of fanciful terms had been devised to refer to the different castas and their offspring. Several documents record these officially designed classifications, which include zoologically inspired terms such as lobo (wolf) and coyote, as well as names alluding to the racial indeterminacy of specific admixtures, including tente en el aire (hold-yourself-in-mid-air), and no te entiendo (I-don't-understand-you).10 While most racial taxonomies list sixteen mixtures, some enumerate fourteen, others nineteen or even twenty. These numerical differences point to the impossibility of definitively categorizing the racially mixed, impeding the creation of a fixed system of classification and representation.
Although most of these terms were clearly not applicable in ordinary communication, they suggest a basic principle: Spanish or white blood is redeemable; Black is not. In other words, while the purity of Spanish blood was inextricably linked to the idea of "civilization," Black blood, bearing the stigma of slavery, connoted atavism and degeneracy. This principle is explicitly stated in an illustrated manuscript by Joachin Antonio de Bafarás entitled Origen, costumbres, y estado presente de mexicanos y phillpinos (1763).11 The author, presumably a Spanish merchant living in Guanajuato, as inferred from the text, offers a description of the different aspects of the colony, including its history, government, industrial activities, forms of entertainment, military guilds, foodstuffs, population, and customs.12 An important part of his manuscript is devoted to the description of the generations of Mexico (fig.1), which are accompanied with illustrations that, in all likelihood, derive from the author's knowledge of the popular casta series (figs. 2, 3, 4). In his system of classification, Bafarás suggests that so long as Spaniards are mixed only with Indians, the blood can be purified. However, the mixture of Spanish or Indian with Black can never again be purified back to Spanish or Indian. In this system of identity-formation, Bafarás emphasizes the supremacy of the white pole to the Black.
http://www.gc.maricopa.edu/laberinto/fall1997/casta1997.htmThere is much more at the link along with the paintings this essay discusses.