As a part of my history studies at FHSU this semester, have been researching Chinese glazes, a part of that research has been the recreation of those glazes from modern materials. Using Nigel Wood’s excellent text; Chinese Glazes; Their Origins, Chemistry and Recreation, I have been attempting to recreate the earliest evolution of these glazes.
To begin the process I had to refine the raw materials. I began with the wood ash as this process takes the most time. I started with half a five gallon bucket of ash from a friend’s wood heater. They burn a mix of soft and hard wood, a great deal of it being scrap and remnants, so not only is the chemical composition difficult to guess, but there was a great deal of impurity, particularly metal, in the mix. To begin I soaked the ash in water. this is a good way to separate impurity and to remove the water-soluble portions of the ash, which would affect its performance in the glaze. To streamline this process Gabe built a large screen of medium mesh.I was able to remove large particles with this, then after this process was complete I drained off the water and dried the ashes for several days.
While that was drying I prepared the clay and acquired materials I could not make myself. The stoneware clay used was a locally sourced stoneware called 200 by Summit Brick which it uses to make a white brick. The porcelain is Laguna’s Babu porcelain. To process the clay I first crushed it with a hammer then ground it fine in a blender.Once the materials were prepped I got to mixing and glazing, the test pieces were made from the bodies used in the glazes, though the 200 has an addition of reclaimed Soldate 60 from Laguna to add plasticity Rather than going to the back of the book and mixing Wood’s already translated tests, I chose to focus on the text and come up with my own basic formulas based on the research found there. Those earliest glazes were composed of Alumina, silica and calcium carbonate derived from either limestone or wood ash. The clay provides the alumina and silica in the mixture. My first test were thought to be the earliest glazes used in high temperature kilns in China. Using the two two different clay bodies I mixed 60% clay and 40% washed wood ash. To add color I also added 2% red iron oxide.The stoneware and porcelain tests on the left are test 1 and contain the stoneware clay is the 200 and the test on the right is the same formula but replacing the 200 with Laguna’s Babu porcelain. The 200 clearly has incidental colorants that are not present in the test mixed with porcelain, and so shows darker.
The nest group used the same 60/40 mixture but instead of using wood ash, I used limestone or whiting as it is more commonly known in ceramics. For this group I also pulled the iron back to 1% because I feared over saturating the color and skewing the tests with the fluxing capacity of the iron.This time the test on the left is mixed with the porcelain and the set on the right with the 200. A major down side to using the 200 in glazes is that it is prepared for brick making before I get it, which means it is full of very heavy grog. Though I did screen it, some small particles escaped and made the bottom of the testers rough and unrefined. The wood ash too, though washed and crushed was not ball milled and so added large particles that did not break down and integrate with the glaze. They are beautiful glazes but could only be used on sculpture without significantly more work in refining the raw materials.
The next group of glazes were derived from the earliest porcelain glazes, and use little wood ash. From the left: 82% Babu porcelain, 18% whiting and .5g RIO 70% Babu porcelain, 30% whiting and .5% RIO 70% Babu porcelain, 28% whiting, 2% wood ash and .5% RIO
The test in the center, number 6, was my favorite from all the the tests, it is a buttery matte with a subtle green color. Adding a full percent of iron would make this glaze a winner on the porcelain body, truthfully none of these is very nice on the stoneware clay, too gritty. Though the fit does seem to work.
For the last four tests I chose recipes from the back of the book, though they had to be somewhat modified to work with chemicals I have available to me. The first two were porcelain glazes, a clear and a northern celadon.These glazes are from later in the evolution of Chinese gazes and are much more complex, very near to their modern counterparts. I had to change these recipes, especially where the author used english ball clays which I don’t have access to. The glaze on the left is #1 in the book and is called porcelain glaze the original glaze recipe asks for Hyplas ball clay which I substituted EPK, feeling that this would be closer in makeup than domestic ball clay. The recipe is:
Potash feldspar 25%; Wollastonite 27%; China clay 12.5%; EPK (sub) 12.5%; Flint 20%; Talc 3%
The recipe on the right is #3, northern celadon, for this glaze I replaced SMD ball clay for EPK, again feeling its properties closer to domestic ball clay.
Cornish stone 56%; Wollastonite 20%; EPK (sub) 20%; Talc 3.5%; Red Iron Oxide 1.5%
These were winners on both clay bodies, I was especially impressed with the “porcelain glaze” on the stoneware, it may be the most beautiful high temperature clear I have seen on this body.
The next tests were a Northern Hares Fur Temmoku (#4 reduced) Again, slight modification was made to the original recipe, for this I subbed 200 for the BBV ball clay on the right and EPK for the test on the left. The original recipe also asks for molochite which is a calcined china clay, which could have been made but since a sub of china clay (slightly more) was allowed, I used it.Cornish stone 42%; 200 (rt) EPK (left) 15%; China clay 15%; Dolomite 15.5%; Flint 17%; Red Iron Oxide 4.5%; Rutile .5%
These were both beautiful, again the test containing 200 was darker and slightly more opaque, but both worked very well.
Thanks to Shane Jarrett for firing these for us, it was a wonderful study.