Cochineros is a petroglyph site on the banks of the Rio Mala, at an elevation of 570 metres above sea level. It is 30 kilometres inland from the coast and 45 kilometres from Huarochiri. Calango, a town known as the site of a petroglyphs described in writing by spanish invaders, lies 12 kilometres down river.
The petroglyphs were visited and recorded by Antonio Nuñez Jimenez in 1976, partially studied by Henry Tantalean in 2010, and included in a photographic record of petroglyph sites by Guffroy in ….
The images are very well preserved, perhaps because the site is difficult to access, as the valley road is on the opposite side of a river which is too high to cross on foot from October to May. Nuñez labels his drawings in reference to stones 1 to 12, though no drawings are recorded for stones 7 and 9. Tantalean introduces another numbering system which is largely Nuñez in reverse. The apple grower farmer who works amongst the stones says there are thirteen stones. I have recorded twenty stones with images and there are probably more. However, the majority of the individual images as well as the largest panels, are found on just five stones.
Neither of the plain words “stones” nor “boulders” fully conveys the magnificence of these rock outcrops. Piedra 11 (following Nuñez’ numbering system) was measured by Henry Tantalean as 3.75 x 10.35 metres (maximum length x maximum width) and the five most important stones have a combined surface area with drawings of one hundred and fifty square metres.
Tantalean began to count and categorize the images on eight of the stones, including the five major ones, and recorded over three hundred images. Nuñez recorded the stones over 36 pages with drawings of over 700 images. Although Nuñez’ record is very thorough and he often includes extra details including a scale, the direction the panel faces, and the rock positions relative to others rocks. This information is almost entirely accurate, but he misses two significant rocks and two major panels, as well as images that are difficult to see except under very specific lighting conditions. The actual number of individual images is likely to be over one thousand.
It is possible to distinguish brighter, whiter drawings and duller greyer drawings on many of the rock panels. Where one image has been drawn over another older image here, the newer image is brighter. This is more evident to the naked eye on some panels – generally vertical or nearly vertical panels facing south or east – than on others, such as flat or north facing panels.
From the overdrawing alone, it is possible to identify different stages in the use of the site.
One panel with clearly differentiated bright and dark images (south facing side of Piedra 11, Figure 1) is two metres high and three metres wide at the base, rising to an apex. Jimenez records some thirty individual images on the panel in his Fig 1488 (footnote). There are several clear overdrawings. For example, three tupus, or shawl pins, have been drawn over a less distinct camelid, and a bird-camelid morph has been drawn over a spiral.
To assess whether the changes in brightness or the patina could be measured quantitatively, photographs were taken of the southern facing panel of Piedra 11 at different angles.
Images were initially taken with a digital camera at an angle to the rockface to avoid directly reflected sunlight, at 1.19 pm and 1.20 pm on 22 August 2016, at angles of 30 and 40 degrees to the perpendicular of the panel approximately.
The brightnesses of the jpg images were compared using freely available scientific software (Fiji) which provides a range of sampling and measurement tools.
After trialling several methods of measurement, a brightness value was generated by averaging the brightness of several areas outlined within different parts of the image.
The software was used to give a quantitative value on a scale from 0 (pure black) to 256 (pure white) for selected areas within the image. The jpeg brightness varied from 220 to 140 pixel value.
Images that are fully blocked out, rather than drawn in outline, were preferentially chosen for the trial as they provide a greater area for measurement. There were several such images on the panel, designated The Old Llama, Tupus 1, 2 and 3, Lobster Men left and right, the Dot Track and the Heart.
The measurements confirmed the hierarchy of brightness that is evident to the naked eye, that is from brightest to darkest, Heart, Dot Track, Tupus, Lobster Men and Old Llama.
The method gave consistent results, within the broad error ranges of the raw data, for mean, mode or median brightness levels. The hierarchy of brightness was the same from the two photographs taken at different angles, and the ratios of brightness were also consistent.
The absolute pixel brightness values from the photographs were not the same, but all gave a similar linear relationship between the different images, against a horizontal scale that could relate to time.
When a camera creates Jpeg images it modifies the raw digital data measuring incident light intensity, so as to create an image more aligned with the non-linear response of the human eye. Typically it adjust the linear pixel brightness data by a power relationship, the gamma function. For many cameras this might mean the jpg pixel value is the raw brightness of a point in the image, raised to the power 2.2. The effect is that the brighter parts of the image are more differentiated, to compensate for the human eye’s reduced sensitivity for brighter images.
To have a linear measurement of image brightness, further trials were conducted with Raw images ( .cr2 files) taken on 30 June 2018 at 12.03 pm (4606.cr2) and on 21 July 2018 at 1.45 pm (5066.cr2, 5067.cr2, 5068.cr2). The results were again consistent, showing that as long as precautions are taken to avoid direct sunlight reflection, the results are not very sensitive to sun position, a month apart, nor to the jpeg adjustment.
Superposed images on the panel, such as the tupus, are brighter than the images over which they are drawn, which suggests the darkening process is time related. The measurements can therefore be used qualitatively to propose a historic sequence for the images.
This would mean that the brightness sequence Heart-Dot Track-Tupus-Lobster Men-Old Llama is a time sequence from most recent to oldest.
If we know the mechanism of the darkening process, and we have some images of known date to calibrate the change in brightness, it might be possible to use the measurements to determine the absolute age of the images.
There is evidence that the darkening process is due to a film growing over the drawings. Such a process has been documented in many desert regions and the films have been studied in detail. The films have also been used, in various ways and with limited success, to date petroglyphs.
A localised film formation is evident on several rock surfaces and panels on the site.
Piedra 1 has a long near vertical panel facing the river. At its foot is a white band above the present ground level (Figure 2). A similar white band at ground level is seen on other stones including Piedras 11 and 4, where is runs continuously. On Piedra 1 it is broken by a dark vertical band which descends from the upper surface of the rock
A kidney-shaped figure which overlaps the band is clearly darkened within the band area. The same effect is seen on several other figures on the site. These observations are consistent with the formation of a dark film on the rock surface, gradually obscuring the drawings.
On Piedra 1, the appearance of the rock surface above and below the kidney supports the proposal of film formation – it has a darker, shinier surface compared to the surrounding rock. It appears to be an area where moisture runs down the face of the rock. This might be from rainfall, moisture from the river when it is at is highest, or condensation from the warm daytime air on the rocks which have cooled overnight.
There are several films which form on rock surfaces in a desert environment which have been widely studied. A dark black film with a high manganese content was first observed by Humboldt on the banks of the Orinoco, and is commonly seen as a coating on rock art in New Mexico. A reddish brown coating appears at other sites (in Peruvian petroglyph sites, Checta and much of Miculla displays this).
The rate of growth of this “rock varnish” has been estimated to be 1 -40 micrometres or microns per thousand years, as an average over 10-20,000 year periods, based on measurements at different sites in different environments.
If a 75 micron coating – equivalent to three coats of paint – were required to entirely hide the whiteness of the drawn image, then these growth rates would cover the drawings in two thousand years, at the maximum rate of growth.
Estimates of the rate of rock varnish growth are questionable and in any case are considered to vary from place to place and even from one side of a boulder to another. I merely observe that the growth rates above above are compatible with the date estimates here.
Fragments of the glossy black rock surface at Cochineros, which can be found on the ground close to some of the stones which are naturally beginning to flake, are weakly ferromagnetic, which might indicate iron or magnesium components.
In order to use the change of brightness due to film formation to support dating estimates for different images, we need consistent film formation across a panel. This requires a flat panel, without run off from an upper surface. The south panel of Piedra 11 (Figure 1) largely satisfies these conditions in its centre.
Consistency of brightness within individual images suggests that the film formation is uniform across the width and height of the image.
In particular, the dot track, which runs for a length of two metres from close to the top to close to the bottom of the panel, appears to have a consistent brightness until the lowest seven dots, which are also smaller. Brightness measurements confirm this.
Similarly the heart extends across 60 cm horizontally and vertically, and appears consistently bright. The white band at the foot of the panel is unbroken, which suggests there are no vertical areas with differential film formation.
The top and the shoulder of the rock shows signs of differentiating brightness, and there are some ridges lower down the surface which may affect the film growth. I have not considered images here to be suitable for measurement.
There is a powerful aid to estimating the ages of drawings on this panel, since there is a modem image, the heart which is dated 1964, which can serve as a calibration point.
In fact, it seems unlikely that this is the date of its drawing, since it is not shown on Antonio Nuñez’ Fig 1488 sketch of the rock surface, probably made between 1972 and 1977. Nuñez was Cultural Ambassador to Peru 1972-1977 and published his four volume work on Petroglyphs of Peru in 1986. So the heart would appear to have been drawn after 1972.
The heart is seen on a photograph by Tantalean which was published in 2010, though it could have been taken a few years earlier.
It could be that JMJR met his partner or got married in 1964, and the engraving was made twenty or thirty years later. For the purposes of calibration, these uncertainties in date do not introduce much uncertainty in the calibration compared to the uncertainty in pixel brightness values.
A second calibration point is provided by the assumption that writing on the rocks could not have continued long after the Spanish invasion. The Spanish reached Pachacamac in 1533. They founded Lima in 1535. In 1571 the Reducciones began, whereby Peruvians were forced to move to new settlements under Spanish control. By 1586 Corregidor Davila Briceño had moved the people 0f 200 Yauyos villages into 39 Spanish centres. In 1608 the Extirpacion de los Idolatrias began its visits throughout the Huarochiri region, destroying sacred sites, and intimidating those who practiced the indigenous religion. In this context, it seems unlikely that people could have continued for long to visit their holy places and leave their marks upon the rocks.
Using the heart calibration date of 1995 plus or minus twenty years, 24 years BP, and the next brightest historic image as the dot track with a calibration date of 1580 plus or minus twenty years, 440 years BP, we get a consistent variation in brightness using jpeg images at slightly different angles to the rock face, and RAW pixel data (without adjustment) from photographs taken at a different date and from different angles.
The calibrated points on a linear graph suggest date estimates which are consistent across two jpg images taken at different angles to the rock face on the same day, and four .cr2 RAW images, three taken on one day covering different areas of the rock panel, and the fourth taken three weeks later.
215.jpg was taken at 1.21 pm on 22 August 2016, 219.jpg at a slightly different angle on the same day, 4606.cr2 taken at 12 pm on 30 June 2018, and 5066.cr2, 5067.cr2 and 5068.cr2 taken on 1.45 pm on 21 July 2018.
They provide age estimates for different images that span over one thousand years, and provide a time sequence for the images on the rock panel. The oldest figures are put at 1000-2000 BP. It can be seen that the range of values for the brightness of our calibrated points leads to a wide spread. More advanced statistical analysis may provide a narrower estimate.
The linear estimate simply assumes that if the image brightness falls, for example, by 20, from 220 to 200, in 400 years, then it will fall by 100, to 120, in 2000 years. In fact if the darkening is caused by a film which grows at a constant rate, the relationship would be exponential. This makes little difference to the ages of the brighter images such as tupus, but would make the old llama and the dark figures somewhat older.
The dating depends on the assumption that the film forms at a constant rate. If its formation is dependent on climatic conditions – temperature, humidity, wind – these are not expected to have changed significantly over the relative short timescale of several thousand years, before the spanish invasion and subsequent deforestation.
An ability to fix the date of any images by an independent method, such as by comparison with known iconography from ceramics or textiles would greatly improve the value of this calibration.
Happily this is possible. Many drawings recall Chancay textiles or Late Horizon images. There are sea-birds drawn on the southern face of Piedra 6 which are similar to Chancay period central coast textile imagery. They have a similar brightness to the tumiforms on the same panel, as well as to the several quadrupeds across the face of the rock, although there is a measurable difference between these three groups of images.
Three fabulous birds, which resemble Chancay textile imagery eg found at Pachacamac, and also reflect engravings on a rock at Lunahuana, in the Cañete river valley to the south, are drawn on three river facing panels of three stones on the eastern, river bank, border of the site. They are amongst the brightest images though a quantitative comparison would help to confirm this.
There is a pair of felines close to ground level on the west side of the southern most stone, Piedra 12, drawn in a style similar to Chancay woven textiles designs.
A pair of monkeys walking along a line or branch, which is similar to Chancay textiles, and is drawn on another panel close to a pair of tupus or shawl pins. The brightness is similar to the nearby tupus. If we assume these tupus are drawn in the same period as those on piedra 11 (they all have similar dimensions, mostly the same design with curling ornamentation on the head of the pin and are drawn as a pair) then our tupu dating on piedra 11 – 750 BP or 1270 CE, is consistent with Chancay imagery.
Highly stylised llamas, drawn with a series of straight lines, are among the brighter images, similar to the tumis and consistent with imagery such as the procession of llamas at choquequirao and other inca llama images.
T-shapes and tumi blades with ornate handles are marked on many rocks, and Tantalean saw this as a reflection of the Inca domination of the coast, so that it would date to 1470 AD, or 550 years BP. Though there are no such images on the central panel of Piedra 11, the tumis are amongst the brightest images on the rocks and overlay older images, although they vary in size, shape, and design.
In summary there are several images across virtually all of the rock panels that resemble textile and ceramics imagery from the Late Intermediate, and they are amongst the brighter of the images, which is consistent with the dating proposed.
As discussed elsewhere, some images on the panel could be related to the worship of Paria Caca which latest date would be around the time of writing of the Huarochiri Manuscript, in and around 1622, before the extirpation. The beginnings of Paria Caca’s presence in the mountains and valley is unknown, but a clue comes from the reference by Extirpador Acosta to one of their founding fathers, Tutay Quiri, whose mummified remains, taken to Lima to be publicly burnt as a gesture of destructive contempt for everything Peruvian, were estimated as being 800 years old, that is from 800 CE.
At the opposite end of the brightness and time scale, there are dark images – those that do not appear as white marks on the black stone surface, but are rather revealed as a rough texture when the light is observed to reflect of the glossy unmarked stone. On the estimated time scales above, these would be 1500 to 2000 years BP.
There are darker camelid images, drawn with four legs and as if running, and in ones and twos rather than in a line with humans, Which could represent wild camelids.
The dark images are most evident when the sun at its northern limits close to June solstice shines on the southern slanting face of Piedra 12. Images that are barely visible under normal illumination (Figure 10) stand out sharply as dark against the shining rock surface (Figure 11). A translation of the photograph to adjust the vertical dimensions shows even more clearly the abstract nature of these images (Figure 12).
A closer investigation of other rocks at Cochineros reveals that several of them have such dark images, though artificial lighting rather than sunlight is needed to observe them clearly.
The majority of the dark images are abstract, geometrical, and not repeated. They show great creativity and variety, in marked contrast to the llamas, tupus and tumis.
For example the central panel illustrated in Figures 11, 12 has 30 abstract images including parallel lines, curves and dots, no two of which are the same. In the same area, the white images consist of four curving tailed quadrupeds (the same image repeated four times), some swallow-like birds, a man with a line of four llamas, and another human figure with one llama, very poorly drawn.
The white images are often lightly traced on the surface whilst the dark images are deeply engraved.
The change in style and subject from the bright to the dark images is similar to the change in images on painted textiles from Chancay period to Middle Horizon, or even Wari abstraction, which would be consistent with the estimated dates above.
However, there do not appear to be classic Wari iconographies such as the occulted eye.
Across all the stones, there are images, perhaps the majority, that are neither bright nor dark. For example, the busy southern face of Piedra 6 has bright tumis, running creatures (foxes?), and 3 Chancay like birds, all bright motifs. The rest of the images are darker and
Tantaleán, Henry. Los petroglifos del Valle de Mala, costa centro sur peruana:
una explicación materialista-histórica. En Rupestreweb,
http://www.rupestreweb.info/valledemala.html 2010