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.
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