Category Archives: clay

Recreating Chinese Glazes

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.IMG_7906IMG_7909I 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.IMG_7912Once 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 plasticityIMG_7927 IMG_7966Rather 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.IMG_0674The 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.IMG_0675This 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.  IMG_0676From 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.IMG_0677These 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.IMG_0678Cornish 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.

Building the House for “The Empty Room”

Construction of the house for the film “The Empty Room” began in early September.  Or original plan was to space the build out over several weeks and fire stories as they dried, but after a test build we determined that the box construction would require more dry time than anticipated so we opted to push the build into one very intense week.IMG_6476As with all projects we began with prepping clay and pressing the molds, one story at a time.  Each story needed about 100 lbs of clay wedged and weighed out into specific slugs to accommodate each mold.  Each floor was about 3 days, clay prep was the first.

IMG_6353 IMG_6351The second day was focused on pressing the molds and preparing the wall for assembly.  This was a huge job, as the pieces are very complex and have many details that needed to be prepped on the same day.  Not only did we make molds for the build, but also many of the tools were custom-made for the project.   This tool was designed to give us perfect cuts on the edges of the walls and floor so we could more precisely control fit.

IMG_6349The day following pressing was assembly.  The floor was put in place first and the corner with the stairs was attached to the floor.  This is the second floor.  The cut outs pictured here will be for the staircase on the floor beneath.

IMG_2067 IMG_2068Once the corner was reinforced and secure, the staircase was attached.  We began with the landing and the bottom half and built up from there.  These pics are also of the second floor and so include a handrail that is not present on the first floor.

IMG_2069 IMG_2073 IMG_2074 IMG_2077 IMG_2031IMG_2083The windows were cut earlier on this story to give us access to the underside as the entire stair well is likely to be shown in the film and needed to fe completely finished.

After the stairs we put on the remaining two walls were applied.  With each wall the corners and other details from the molds had to be tuned back up as handling was somewhat damaging.

IMG_2021Once all four walls were in place, the flange was attached to the top and cutting windows and clean up and finish work could be done.

IMG_2033 IMG_2042 Another thing we learned from the test build was that the walls wanted to move quite a bit during the drying process.  To control this to some degree Gabe devised a cap to fit into the flange and stay with the floor throughout its shrinking and firing process.  This was a fairly last-minute addition to the group of molds and had to be resolved quickly, so the original was made from a combination of wood and clay.

IMG_6442 IMG_6454The first two floors were very similar and so we could build a skill set from one two the next and refine the process.  The third floor was another matter, There are far more windows on this floor and another wall inside the structure.  It also has a large facade and a roof.  Mold prep was the same in many ways, but with molds we had not yet used in an order that we had not tested, this was the greatest challenge of the project.

IMG_6481 IMG_6482 IMG_6485 IMG_6489 IMG_6490 IMG_6496 IMG_6499 IMG_6504Because they were made so close to one another we were able to see them wet all at once, which made a great group.

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Pinch Pots

pinch pots

These pinch pots, by Kate Tremel, capture exactly what I love about pinched forms.  Delicately crafted, the rims become landscape and describes perfectly the action of the fingers in making.  Simple glazing accentuates the directness of form.  The only addition to these wonderful bowls, is subtraction in the form of pierced openings in the clay wall which allows the element of light to play in the object in a way that is difficult to achieve in clay.

Simple is truly the defining characteristic of pinch pots, while it is true that making a pinch pot is relatively easy, that makes it all the more challenging to make work that displays innovation and integrity.  One artist who does that perfectly is Priscilla Mouritzen, South African born and living in Denmark, Priscilla’s wood fired pinched forms are some of the finest pots I have ever seen.  The quiet simplicity of form coupled with her rhythmic decorations and the touch of the wood kiln, make each bowl feel like a precious individual.

http://design-mind.blogspot.com/2012/05/priscilla-mouritzen-ceramics.html

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Especially for my students, here’s a nice video done by Ceramic Arts Daily that gives a good beginning on the basic technique and suggests a direction to expand.

 

Clay Mixing

clay mixing 6

As we began preparing for classes one of our top priorities was to get clay.  We are pretty young as a studio and so many of the things basic to a studio need to be acquired.  We’re also as a pretty young business and we don’t have a lot of capital, so getting what we needed on the cheap was another priority.  Fortunately we had two resources to pull from.  From my former business we had about 400 lb. of a clay body called 200.  This clay is a brick body from the local manufacturer that my ex-husband and I would screen and mix into a workable throwing body.  We also had about 400 lb. of soldate 60 scraps left over from previous sculpture projects.  The soldate is a Laguna Clay body with a 60 grit sand, it is a fantastic hand building body.  On the surface this is a simple solution to our needs, but the condition of all that clay was nowhere near usable.

The 200 had been bagged in 30 lb. lumps that dried out completely, The body is very open because of the brick grog and so has a much shorter storage life than other clay bodies.  So that is where Gabe began,  taking those large heavy blocks of clay and breaking them apart and then crushing the bits to be slaked down in water.

photo 1-6 clay mixing

The clay was allowed to soak in the water for a few days so that it could be totally saturated. Gabe then put together a drying frame to prepare the clay for mixing.  The frame was 2×2’s and a large piece of canvas.  This size was needed so we could get it through the door, the wet clay should not be allowed to freeze as it pulls the moisture inside to the surface, making the clay a slimy mess.  We filled the drying frame with the slaked clay in batches of about 200lb.

photo 3-4 clay mixing photo 4-3 clay mixing photo-6 claymixing

But of course the project took place at the end of December and the beginning of January so freezing was a part of this project.  The ice crystals cutting through the super wet clay was one of the most beautiful things I’ve ever seen.  Of course it did need to be remixed a bit, but because it was so wet, this was not too much of a problemclay mixing 5

Once the 200 was bagged and waiting, it was time for the soldate.  Gabe’s job here was not as tough as the soldate was in slightly better shape.  Some did have to be slaked down, but much of it could be mixed straight from the scrap bags.  It did all need to be weighed as the plan for the new clay body was a straight 50/50 mixture.

clay mixing 4

One the soldate was prepped and bagged we were ready to begin mixing.  The pug mill was loaded with about 150 lb. at a time, 75 of 200 and 75 of soldate.  An even mixture was a priority so the clay was run in 4 batches and then bagged again at 25 lb.  He then re ran them through again, one bag from each batch.clay mixing 2

As the batches ran, it was my job to weigh, wedge and bag the clay.

clay mixing 3

Once the mixing was finished it needed to age, though we were forced to use it for classes right away.  After waiting a couple of weeks I sat down at the wheel to give it a try.  This is a 10 lb. pot,  the clay is still young, but aging into a great clay body.photo-7

and here are some small vases for the same project, more words on this to come.

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