Holy crap, I’ve finally found a youtube video about the Gran Coclé. Thank you, I’ve been trying to learn about them just as someone interested but haven’t found much easily accessible stuff.
PANAMA PURPLE: Investigating a Misunderstood Technique Kathryn Etre, Andrew W. Mellon Assistant Conservator Michael C. Carlos Museum, Emory University You Tube Video, uploaded February 2, 2016 During the years 500 to 1100 AD, a polychrome slip design with three or four colors was being used in the Coćle region of Panama. The distinctive slip color of this period is purple. Although other areas in Central and South America have purple hues in their pottery, these other purples are more maroon. The Panama examples have a blue-gray hue. What is this pigment exactly, and how was this unusual hue produced? Numerous printed sources discuss the designs on these ceramics, but there are no recent studies on their production technology. Many suggestions about the materials in these unique ceramics have been stated as fact, but none of these suggestions are supported with analytical evidence. The following presentation will describe research conducted to better define the production technology of these ceramics, in particular the purple slip. (1:07) The Michael C. Carlos Museum of Emory University has nineteen ceramics from the Coćle region with this purple slip. Most of the analysis for the study was conducted on an originally kilned pot, which provided easy access to break edges and worn slip for sampling. The purple slip is in actuality not purple (1:30). The Munsell color charts place all of the purple slips within the gray-red range. The Munsell Color System consigns values to every color based on the color’s hue, lightness and color purity. As everyone sees and describes color differently, this system allows colors to be discussed objectively. For clarity however, this slip will be referred to as purple. (1:50) Under polarized light microscopy, the particles of this purple pigment are homogeneously purple, and between 0.5 micrometers to 0.1 micrometers in diameter. This appearance reveals that the purple pigment cannot be a mixture of red and blue minerals, but rather is itself a purple compound. (2:09) The only scientific analysis of these slips on these ceramics was conducted by Rutherford Gettins, who is the father of conservation science, and reported in archaeologist Samuel Lothrop’s 1942 “Coćle: An Archaeological Study of Central Panama.” Gettins identified the slips of these ceramics as red orche for red, violet hematite for purple, manganese for black, and kaolin, or another white clay mineral, for white. Analysis of the crystal structure and the elemental composition of these slip minerals confirmed Gettins’ identifications of the red orche and manganese black. The purple is iron-based, as seen in this x-ray flourescence spectra (2:50). There are very few purple mineral colorants, and even fewer containing iron. The iron-containing purple minerals are purpurite, vesuvianite, crocus martis, and natural violet hematite. Purpurite, vesuvianite, and vivanite, a blue mineral that becomes purple upon heating, can all be discounted since netiher manganese or phosphorous occur in the elemental composition of the purple pigment on Coćle ceramics. Although the sulphur in crocus martis could have been burned off during firing of the ceramic, crocus martis becomes maroon when fired, instead of maintaining the gray-purple hue. (3:37) This tile shows a few of the suggestions, both from print and by person, that were tested. Many of these can be discounted as they do not contain iron, contain elements not seen in the analytical spectra, and or do not become purple upon firing. However, as Gettins identified, the purple pigment appears to be a Violet Hematite. The question is why is the hematite purple? The color of hematite particles is dependent on their size: bright red between 0.1 micrometers to 0.2 micrometers, and purple between 1 to 5 micrometers. As mentioned previously, the purple particles in the slips studied are much smaller, 0.5 micrometers to 0.1 micrometers. (4:25) These are samples of the purple and red slips from one of the Carlos Museum’s Coćle ceramics. As you can see, the particle sizes of the red and purple slips are similar. Thus the hematite in the purple slips cannot be naturally purple, due to its small particle size. Gettins mentioned that violet hematite may have been derived from red hematite but did not explain how this shade was derived. The dehydrated state of the purple slip, as noted by Gettins, could be created by two different processes: either heating in a reducing atmosphere and then reheating in an oxidizing atmosphere, or heating at a high temperature. (5:06) These are two test tiles: one with hematite fired in a reducing atmosphere on the left, and the other with hematite fired in a high temperature on the right. Since both the red and purple slips contain hematite, the alteration of this hematite pigment must occur separately from the firing of the vessel itself, to avoid altering the red slip as well. The white slip was applied first, then the colored slips, and finally, the black outlining, but there is no consistency in the application of the purple and red pigments. If the alteration of the purple pigment occurred during the final firing of the pot, the red slip, also composed of iron oxide, would become purple under these conditions as well. If the purple slip was always added first, or last, a change in the firing conditions could be possible. However, when the overlap of the various slips is examined, sometimes the red pigment is seen applied over the purple, and sometimes the purple overlaps the red, and sometimes both occur in the same ceramic. Therefore, the hematite must have been turned purple first and then applied as slip to the pot. It is possible that nodes of hematite were buried in coals to produce an oxygen-deprived, or reducing, atmosphere. Once the purple color was reached, the nodules could be ground to produce pigment for the slip. (6:32) A nodule of unfired hematite is on the left, and a nodule on the right is a piece from the same stone heated in a reducing atmosphere with the ground pigment in the front. In this way a purple color could be achieved without needing a high temperature. (6:47) To recreate this reducing atmosphere, a piece of hematite was heated in a pitfire. The fire was smothered by dirt and left to cool. Once the hematite was cool, it was ground and applied as slip on a test tile and the test tile fired. (7:01) Although an appropriate color was achieved using this technique, if you compare the test tile to the detail from one of the Carlos Museum’s ceramics, magnatite was present, as seen in this x-ray diffraction pattern. None of the four ceramic samples from the Carlos Museum’s collection had any magnatite. (7:24) If a reducing atmosphere was not the cause of the dehydrated hematite of the purple slip, the other possibility to achieve the purple hematite is a high heat. Hematite will turn gray at high temperatures. (7:31) The tile on the left is unfired, and the tile on the right is a copy of the one to the left, but heated at a high temperature. Note that the iron-based pigments have a blue-gray hue. Based on the presence of montmorillonite in the body of the ceramic and the appearance of the hematite nodules used as temper, the firing temperature of the Coćle ceramics is between 700 to 860 degrees Celsius. Montmorillonite degrades at 860 degrees Celsius, and the hematite nodules show irridescence and bubbling, which occurs around 700 degrees Celsius. However, a temperature of at least 900 degrees Celsius is necessary to turn hematite gray, supporting the conclusion that the hematite was turned purple separately from the firing of the ceramic. Scholars have doubted that pre-Columbian Panamanians could achieve such a temperature during firing due to the lack of evidence of kilns, but the higher temperature could have been created through the use of a brazier, as used in metalwork. (8:39) Cast gold, seen in this example from the Penn Museum, was burgeoning at the time of the introduction of the purple slip. A temperature of at least 1000 degrees Celsius was necessary to melt the high purity gold used in cast Panamanian gold work. (8:55) A sample of hematite was heated in an oxygen-rich environment at a high temperature and the hematite turned purple. The unfired hematite is on the left, the fired hematite is on the right, with a ground example on the front of the fired nodule. Note the purple hue. After being ground, painted on the test tile, and the tile fired, the purple color of the slip remained. This purple was closer, as seen on this slide, to the range of the Munsell colors of the four-colored polychrome pots at the Carlos Museum than the hematite which was reduced. (9:32) More significantly, the x-ray defraction spectra of the recreated purple pigment showed no peaks for magnatite, and the spectrum was similar to the XRD patterns of the four Panamanian pots tested. CONCLUSION (9:44) Purple has been equated with luxury and power in many cultures due to the rarity of purple in nature, and the amount of time necessary to produce purple artifically. The time and resources needed to create the purple pigment, and the possible association with gold production, places extra significance on the use of purple in Coćle ceramics. Through a combination of experimental archaeology, and analytical techniques, the firing temperature of the Coćle ceramics is between 700 to 860 degrees Celsius, and the unusual purple pigment is hematite heated to a high temperature of at least 900 degrees Celsius, thus providing the analytical evidence for the manufacture of these techniques.
As a Cocle descendant, this is amazing. Anything that explains the world of my ancestors is appreciated.
Holy crap, I’ve finally found a youtube video about the Gran Coclé. Thank you, I’ve been trying to learn about them just as someone interested but haven’t found much easily accessible stuff.
PANAMA PURPLE: Investigating a Misunderstood Technique
Kathryn Etre, Andrew W. Mellon Assistant Conservator
Michael C. Carlos Museum, Emory University
You Tube Video, uploaded February 2, 2016
During the years 500 to 1100 AD, a polychrome slip design with three or four colors was being used in the Coćle region of Panama. The distinctive slip color of this period is purple. Although other areas in Central and South America have purple hues in their pottery, these other purples are more maroon. The Panama examples have a blue-gray hue. What is this pigment exactly, and how was this unusual hue produced?
Numerous printed sources discuss the designs on these ceramics, but there are no recent studies on their production technology. Many suggestions about the materials in these unique ceramics have been stated as fact, but none of these suggestions are supported with analytical evidence. The following presentation will describe research conducted to better define the production technology of these ceramics, in particular the purple slip.
(1:07) The Michael C. Carlos Museum of Emory University has nineteen ceramics from the Coćle region with this purple slip. Most of the analysis for the study was conducted on an originally kilned pot, which provided easy access to break edges and worn slip for sampling.
The purple slip is in actuality not purple (1:30). The Munsell color charts place all of the purple slips within the gray-red range. The Munsell Color System consigns values to every color based on the color’s hue, lightness and color purity. As everyone sees and describes color differently, this system allows colors to be discussed objectively. For clarity however, this slip will be referred to as purple.
(1:50) Under polarized light microscopy, the particles of this purple pigment are homogeneously purple, and between 0.5 micrometers to 0.1 micrometers in diameter. This appearance reveals that the purple pigment cannot be a mixture of red and blue minerals, but rather is itself a purple compound.
(2:09) The only scientific analysis of these slips on these ceramics was conducted by Rutherford Gettins, who is the father of conservation science, and reported in archaeologist Samuel Lothrop’s 1942 “Coćle: An Archaeological Study of Central Panama.” Gettins identified the slips of these ceramics as red orche for red, violet hematite for purple, manganese for black, and kaolin, or another white clay mineral, for white. Analysis of the crystal structure and the elemental composition of these slip minerals confirmed Gettins’ identifications of the red orche and manganese black. The purple is iron-based, as seen in this x-ray flourescence spectra (2:50).
There are very few purple mineral colorants, and even fewer containing iron. The iron-containing purple minerals are purpurite, vesuvianite, crocus martis, and natural violet hematite. Purpurite, vesuvianite, and vivanite, a blue mineral that becomes purple upon heating, can all be discounted since netiher manganese or phosphorous occur in the elemental composition of the purple pigment on Coćle ceramics. Although the sulphur in crocus martis could have been burned off during firing of the ceramic, crocus martis becomes maroon when fired, instead of maintaining the gray-purple hue.
(3:37) This tile shows a few of the suggestions, both from print and by person, that were tested. Many of these can be discounted as they do not contain iron, contain elements not seen in the analytical spectra, and or do not become purple upon firing. However, as Gettins identified, the purple pigment appears to be a Violet Hematite.
The question is why is the hematite purple? The color of hematite particles is dependent on their size: bright red between 0.1 micrometers to 0.2 micrometers, and purple between 1 to 5 micrometers. As mentioned previously, the purple particles in the slips studied are much smaller, 0.5 micrometers to 0.1 micrometers.
(4:25) These are samples of the purple and red slips from one of the Carlos Museum’s Coćle ceramics. As you can see, the particle sizes of the red and purple slips are similar. Thus the hematite in the purple slips cannot be naturally purple, due to its small particle size.
Gettins mentioned that violet hematite may have been derived from red hematite but did not explain how this shade was derived. The dehydrated state of the purple slip, as noted by Gettins, could be created by two different processes: either heating in a reducing atmosphere and then reheating in an oxidizing atmosphere, or heating at a high temperature.
(5:06) These are two test tiles: one with hematite fired in a reducing atmosphere on the left, and the other with hematite fired in a high temperature on the right. Since both the red and purple slips contain hematite, the alteration of this hematite pigment must occur separately from the firing of the vessel itself, to avoid altering the red slip as well. The white slip was applied first, then the colored slips, and finally, the black outlining, but there is no consistency in the application of the purple and red pigments. If the alteration of the purple pigment occurred during the final firing of the pot, the red slip, also composed of iron oxide, would become purple under these conditions as well. If the purple slip was always added first, or last, a change in the firing conditions could be possible. However, when the overlap of the various slips is examined, sometimes the red pigment is seen applied over the purple, and sometimes the purple overlaps the red, and sometimes both occur in the same ceramic. Therefore, the hematite must have been turned purple first and then applied as slip to the pot.
It is possible that nodes of hematite were buried in coals to produce an oxygen-deprived, or reducing, atmosphere. Once the purple color was reached, the nodules could be ground to produce pigment for the slip. (6:32) A nodule of unfired hematite is on the left, and a nodule on the right is a piece from the same stone heated in a reducing atmosphere with the ground pigment in the front. In this way a purple color could be achieved without needing a high temperature.
(6:47) To recreate this reducing atmosphere, a piece of hematite was heated in a pitfire. The fire was smothered by dirt and left to cool. Once the hematite was cool, it was ground and applied as slip on a test tile and the test tile fired.
(7:01) Although an appropriate color was achieved using this technique, if you compare the test tile to the detail from one of the Carlos Museum’s ceramics, magnatite was present, as seen in this x-ray diffraction pattern. None of the four ceramic samples from the Carlos Museum’s collection had any magnatite.
(7:24) If a reducing atmosphere was not the cause of the dehydrated hematite of the purple slip, the other possibility to achieve the purple hematite is a high heat. Hematite will turn gray at high temperatures. (7:31) The tile on the left is unfired, and the tile on the right is a copy of the one to the left, but heated at a high temperature. Note that the iron-based pigments have a blue-gray hue. Based on the presence of montmorillonite in the body of the ceramic and the appearance of the hematite nodules used as temper, the firing temperature of the Coćle ceramics is between 700 to 860 degrees Celsius. Montmorillonite degrades at 860 degrees Celsius, and the hematite nodules show irridescence and bubbling, which occurs around 700 degrees Celsius. However, a temperature of at least 900 degrees Celsius is necessary to turn hematite gray, supporting the conclusion that the hematite was turned purple separately from the firing of the ceramic.
Scholars have doubted that pre-Columbian Panamanians could achieve such a temperature during firing due to the lack of evidence of kilns, but the higher temperature could have been created through the use of a brazier, as used in metalwork.
(8:39) Cast gold, seen in this example from the Penn Museum, was burgeoning at the time of the introduction of the purple slip. A temperature of at least 1000 degrees Celsius was necessary to melt the high purity gold used in cast Panamanian gold work.
(8:55) A sample of hematite was heated in an oxygen-rich environment at a high temperature and the hematite turned purple. The unfired hematite is on the left, the fired hematite is on the right, with a ground example on the front of the fired nodule. Note the purple hue. After being ground, painted on the test tile, and the tile fired, the purple color of the slip remained. This purple was closer, as seen on this slide, to the range of the Munsell colors of the four-colored polychrome pots at the Carlos Museum than the hematite which was reduced. (9:32) More significantly, the x-ray defraction spectra of the recreated purple pigment showed no peaks for magnatite, and the spectrum was similar to the XRD patterns of the four Panamanian pots tested.
CONCLUSION (9:44)
Purple has been equated with luxury and power in many cultures due to the rarity of purple in nature, and the amount of time necessary to produce purple artifically. The time and resources needed to create the purple pigment, and the possible association with gold production, places extra significance on the use of purple in Coćle ceramics. Through a combination of experimental archaeology, and analytical techniques, the firing temperature of the Coćle ceramics is between 700 to 860 degrees Celsius, and the unusual purple pigment is hematite heated to a high temperature of at least 900 degrees Celsius, thus providing the analytical evidence for the manufacture of these techniques.