Casas Grandes glaze tests # 8 and #34

POLYCHROME: art work based on several solid colors, usually utilizing traditional designs.  American Southwest Polychrome generally is reds (which vary from piece to piece from almost yellow to almost orange) defining areas, blacks defining line against a back ground of white, represented by white slip coverings over native or reddish earthenware clay bodies (Mike Hiler's defination)

I have certainly been making a lot of earthenware glaze tests this quarter and I want to talk about them for a minute to give Rachel a better idea of what I've been doing?

Casas Grandes jars are ancient, vibrant, poly chrome, and inspiring.  I suspect there was a lot of specialization associated withe manufacture of these unique pottery jars, but that is just conjecture.  In any case, anyone who looks at them, even superficially, quickly comes to the conclusion that it would be extremely hard to copy this art form, either from a technical standpoint or an artistic standpoint.  It is well known that the "new" Casas Grandes/Mata Ortez pieces made currently in the American Southwest are just a little too perfect and the images are jumbled much as if someone from a future generation mixes up words on a page and imagines they impart some meaning similar to the original pieces.

But nevertheless, the problem for me at this stage is to create white slip covered jars of high quality that are suitable for artists to paint images (Casas Grandes inspired or not).  The jars must be thin walled, light, but structurally sound,,, much like an artists canvas must be able to stay together and keep the canvas tight.  I have been using Dakota red clay, and building up jars from rolled strip coils.  This guarantees uniformity of thickness.  On this surface I apply a white slip,,, so far so good,  However, without a spray application the white slip is difficult to apply smoothly.  The original method I tried was to apply the slip with a brush and then sand it smooth when the jar is green.

Burnishing:  Everyone says that the original Mata Ortez  surfaces were burnished but I disagree.  If colors are burnished, the lines are obsecured and the old jars have anything BUT obsecured line.  Also, if only the white slip covering is burnished, the pots are too smooth and compacted for good color stain application.  But, in the end we realize that the ancient potters did not have sand paper, so what's with that???

(Note firing cones for various temperatures inserted in some of the clay tests above)

Sanding the surface of a green slip is problematic in that it is very easy to sand through the unfritted slip covering.  Next thought is to bisque the slipped jar and sand the bisque covering.  This works best though the surface, once smoothed, is a bit buff.  The bisque sanded slip takes color stains well, allows for good lines, and resists scratching of application tools.  Also, it is easy to sketch on sanded and fritted white slip covering with pencil and the pencil lines are erased very completely with a cone 06 firing.

So lets see where we are with this reasoning:  White slip coverings are best sanded after firing and colors are set with subsequent firings.  In other words, there is the biscuit firing to harden the jar and slip for handling and painting and  then there is the finished firing(s) of the pot to set the colors (Black and red over white).  But couldn't we fire the bisque firing just high enough to make the pot stronger but low enough to speed up sanding this surface.  To that end, I consulted the Daniel Rhodes Bible of Ceramics, "Clay and Glazes for the Potter".  In this wonderful classic he describes a glaze test to determine the proper and the minimum bisque cones temperatures to fire a particular clay, called the "Water absorption" test (page 311).  Basically, this test measures vitrification of various bisque temperatures, to assess what is enough to produce pieces strong enough to handle for glazing but unvitrified enough to accept glazes or stains.  Here are some photos of my ongoing tests.

Another aspect of Poly chrome is the problem of simply replicating the wonderful colors and surfaces of the ancient masters.  To that end I have performed numerous color and surface tests.  Produced cone 06 clear glazes are too smooth, and the untreated surfaces (over the slips) are too rough to compare to the old pieces.  I have done numerous flux experiments and it seems to me that the best "light flux covering" is Gerstle Borate with White Slip, 1-1.  Also, it is best to add a bit of Dakota red to the base slip, AND, I like white slip is I add Gerstle Borate ALSO to it around 3-7.  This gives a bit of off-white and encourages some shine in the finished surface.

As far as colors I find that commercial back stains work best for lines.  I have given up on trying to produce suitable reds from Iron Oxides and am going with Rhodes in that respect by experimenting with Mason Stains.  Mason sells a color chart/guide which is invaluable, it is now just up to some more testing to get a base red that I can alter (between orange and yellow) suitably. 

Wouldn't it be grand if I could replicate this painting below on a Casas Grandes style jar, using yellow instead of black and blue instead of the reds associated with Polychrome.   I don't think you have to worry, it'll never happen!  

All photos in this post are by Mike Hiler

And so, as the sun sets over the western horizon, I'm looking at another month or two of color and surface testing.  By that time I hope to have several white slip jars to accept a wide variety of surface designs.  I hope to have at least one pot ready for the spring DOVA show at Larson.  Wish me luck.  

The Clay form as a canvas for images

This post deals with the question about describing a technique or process I have worked with this quarter.  I want to talk about the Mata Ortiz/Casas Grandes pottery and the unique way the ancient SW natives (and their North central Mexican relatives).  Here is an example:

This is an earthenware pot around 10" X 10" which is covered with a white slip and the design is painted over the top.  I'm guessing it is low fired with natural slips and stains.  This pot is typical of the surface designs in this area around 1000 AD.  Now let's look at what developed from this form a few hundred years later: 

what was one color over the white slip surface has become a true "Polychrome" with black and red slips over the surface in very interesting designs.  Looks easy enough, but it proves to be more of a practical problem in application. 

I reviewed the Mata Ortiz shards of a local artist and discovered that they are is truly very thin, and the white slip covering is relatively uniform. The lips of the pots were a bit thicker, indicating that they actually used these paintings some for (possible) practical uses.  They could also have been used for burials or other ceremonials?  Basically, todays archaeologists have no real idea what the utilitarian nature of this stuff is? 

In trying first to create suitable jars for slip covering/design application, I discovered that slips are much harder to apply when the slip surface is burnished.  For this reason I have tried sanding it to achieve a smooth surface.  It seems it is best to bisque the pot and then sand it with water to avoid dust.  Of course, the natives, working outside, would not have been particularly concerned with dust. Also, doubtful if they had high quality sand paper? 

After making a few of these jars (between 10" and 12" diameter) it is my guess that there was some specialization going on.  It seems that creating these stone canvasas in 1100 AD would have requaired pot builders specializing in the high quality displayed here AND specialized surface decorators.  I suppose in a primitive studio an artist could construct and fire a couple of jars.  I once visited Choco Canyon, NM and judging by the sheer volume of shards, that the natives either broke a lot of pots, or were unconcerned with having to replace these pots frequently.  Some areas are literally paved with shards. 

Back to process.  First of all, lead pencil marks completely disappear when fired to cone 06.  Also a wood fired kiln would have required a very tight fitting sager for firing this clean.  The application of a consistent red slip would also have required much cultural continuity in the pottery trade. I have no idea what the design painters were thinking when they did these surface embellishments.  They seem almost humorous and current, more like something from cubism.  

Also, the artistic talent required to get this detail with hand made slips and hand made brushes is truly amazing.  The consistency of line and form on these surfaces is incredably difficult to achieve, particularly on a three deminsional surface.  I don't see any crowding or compromise with the form so planning must have been parimount.  

Here we are back at a black slip on white body, with a bit of red color on the pot lip.  The reds, from pot to pot, vary from almost yellow to almost orange, and always a bit redder than is possible with just red iron oxide.  I am guessing specialists mined and processed these slips for the artists. 

Bowls were more common at the earlier phases of this ceramic era. With bowls the primary designs were inside the bowl.  I'm guessing this was one step in the evolution of the "surface for design" tradition.  Cooking in these utinsels would have resulted in smoke blacking, which is uncommon with the pieces I have seen photographed. 

Another bowl interior

and a fanciful figure jar.  Aside from the primitive characterization, these figurines are surprisingly lifelike and expressive, suggesting individual representations.

Naturally, like myself, other modern potters have been impressed with the ancient tradition of SW polychrome and tried to replicate it on pottery. I show these successful, modern approaches, both to illustrate their success and to illustrate their lack of success.  They have replicated the technical intensity of the pieces, but are too perfect to capture the aliveness of the originals.  The edges are too perfect, the use of stencils is evident, and the colors are too uniform.  

check out the next piece for the contrast of new and old: 

and finally, here is a modern photo illustrating the setting in which the original pieces were made.  This is a thunderstorm taking place over a site near Casas Grandes.  

Are there other technique and process answers to gleen from the old pottery.  I'm guessing it will be very hard to  replicate their process and remain true to the present.  The modern potter has electric kilns and can thus avoid reduction firing.  They have a modern tradition of ceramic color supply houses to solve the problems of mineral stains.  And, practically anything can be painted on the 3D surface as long as the artist considers that all scenes fold back on themselves side to side and top to bottom.  I  hope to have a few pots to show in a future post around the middle of April.  Stay tuned.