Here are a couple of sets I made using concrete as a glaze material. It was pretty simple to make. The project began after finding two concrete paving tiles in a construction rubble dump. The larger one I kept for the bases, and the other I busted with a sledge hammer into gravel sized chunks. The gravel went into a bisque kiln, and the remaining slab went into the brick saw to get cut in half. Once the calcined concrete came out of the bisque, the friable powder went into the ball mill and ran for a relatively short 8 hours. After sieving out the remaining sand and large pebbles, I had myself a pretty nice looking glaze slurry. Overnight I noticed a lot of settling, I added a small bit of epsom salt, and what I guessed to be about 1-5% by weight of bentonite. It still settled a bit, but not so much that you couldn’t use it. The application of the glaze was dipping, with a bit of spraying to build a thicker layer of glaze on the top half of each piece.
Matt was born in Carbondale, Illinois and grew up in Southern Indiana. In 1999 he was introduced to ceramics in high school. Matt earned his BFA in Ceramics and Art History from Indiana University in 2007. During this time he spent significant time living and traveling in China, studying the history and technology of Chinese porcelain. After graduating from IU, he spent several years living in Seoul, South Korea. Before coming to Graduate school at USU, Matt was a ceramics artist in residence at the Armory Art Center in West Palm Beach, Florida. He was the first recipient of the USU X-STEM fellowship, and his research involves material science, geology, and ceramics.
Daily life plays an important role in what I make and why. The needs of the kitchen and home are for me, like many potters, a useful starting point for conceiving specific utilitarian forms. I make a lot of cups, bottles, and drinking vessels. Lately I’ve been interested in the idea of designing and making these vessels in sets. For me, there’s nothing better than gathering with a group of friends, eating, drinking, and using handmade ceramics. I’m motivated to make objects that enhance these experiences and enliven domestic spaces.
My work explores the intersection of ceramics, material science, and geology. In my mind’s eye, glaciers give way to icy celadon glazes, volcanoes ooze magma as molten glazes cascade down curves and roll off edges, crystals grow and forms take shape when conditions are right. I’m an avid rock hound, and for the past three years I’ve explored the mountains and landscapes of Utah, Idaho, and Montana. There are many gemstones that have analogues in ceramics – and much of my research has been centered on studying and understanding the underlying science of materials and firing processes. For me there is something incredible and romantic about the idea of transforming rocks and dirt into beautiful things.
In the end I strive to integrate my desire to make utilitarian pottery with a love of materials and nature. What drew me in and keeps me interested on a daily basis are the endless variations possible in ceramics. The idea of constantly searching for new possibilities is at the heart of who I am and why I do what I do. At the same time, I love the constant challenge of pairing forms and surfaces, sourcing from the history of ceramics as I source materials from my local surroundings. I think my strongest work finds a balance between all of these ideas, and my hope is that my work evokes a similar curiosity in the people who see and use it.
Pyrosynthesis: n. synthesis or creation initiated by or resulting from the action of heat.
I like to joke that I’m equal parts artist, pyromaniac, rock hound, and nerd. Add to that an interest in history and technology, along with a penchant for experiments and testing, and it describes who I am and what I do quite neatly. As a graduate student in ceramics at Utah State I’m in the perfect place to satisfy all of these interests. For the past three years I have specialized in the transformation of common raw materials into ceramics through the action of heat and fire – hence the title. There are a lot of parallels between what I endeavor to do, and what the alchemists of ancient history sought to do, namely to turn lead into gold. In my case, I’m interested in the transformation of locally abundant rocks and dirt into objects of beauty and interest.
This exhibition, then, is a culmination and presentation of my work on this subject. To explain it simply, all of the work in this gallery has at least one component of a prospected (dug up or picked up off the ground and drug back to my studio) material utilized in the finished piece. The best example is the granite bottle and cup set on the granite slab. In this piece, the glaze is made entirely out of the finely ground up granite rock dust. Coarser granite rock particles were incorporated into the clay body, thus providing black speckles on the unglazed clay surface. The base, too, is a broken granite boulder that has been cut and polished flat to provide a stone surface for the ceramic objects to live on. My hope with these combinations is to draw a direct connection between the ceramic object and the materials they come from. For me, the novelty of melting rocks in a ceramic kiln never gets old – each experiment generates still more new questions than answers, and Utah has been an amazing place to find all kinds of interesting materials. I’ve included 9 of the most interesting materials that have captured my interest.
Starting just to the right of this statement, I’ve included several piecess to help give context to my process and research and shed light on how the finished pieces come about. I should mention, too, that I took all of the 2 dimensional images with the Scanning Electron Microscope here on campus. I often study my experiments and tests for a long time before they end up on finished pots, and the SEM has given me the ability to analyze and learn about the materials and firing process in a way that I still can’t believe. Not only are these images a wealth of information and data, but from an artistic standpoint, I see them as dramatic landscapes and images of incredible beauty. Finally, the pots themselves are at the heart of everything. Over the course of my graduate studies at Utah State my sense of design and craftsmanship has been challenged like never before, the result of which is a body of work that is hands down the best I’ve ever made. Thanks for coming in and having a look around.
From Top to Bottom, Left to Right.
Manganese Saturated Kaolinite/Halloysite from near Eureka, Utah.
Manganese is a very interesting element, and provides some wonderfully interesting surfaces. In certain conditions it can yield dramatic rainbow iridescence. Small additions account for the optical phenomena in the iridescent Hare’s Fur Glazes as well as the Manganese Saturate Glazes.
Quartzite from Willard Canyon, Near Brigham City, Utah.
This is a rather interesting flavor of Quartz, having trace amounts of Chromium, which accounts for the lovely green color. It provides a very high concentration of Silicon Dioxide (glass) in glazes. It was used in the dark green Basalt Celadon glazes.
Dolomitic Limestone with Calcite from Dry Canyon, Logan, Utah
The first material I began experimenting with at Utah State, this material is used in glazes as a glaze flux – which is to say, it’s a material that lowers the melting temperature and promotes flowing, dripping glazes. It’s used in all of the black Oilspot and Hare’s Fur glazes.
Travertine from Porcupine Reservoir, Utah.
I picked this stuff up not knowing what it was, but fascinated by the texture. I later learned what it was and that it formed in chaotic hydrothermal conditions, you could think about this material as nature’s very own hard water deposit. Similar to the Dolomite, it acts as a flux in glazes. It was used in conjunction with the Dolomite and Quartize on the bluish grey teapot.
Black Schist from Willard Canyon, near Brigham City, Utah.
Essentially a metamorphosed clay or shale, this flavor of slate contains some really beautiful pyrite (fools gold) inclusions. By itself it is refractory and unappealing, but with a 10% addition to a celadon base glaze, it provides a beautiful sky blue. You can see the blue and the pyrite inclusions on the blue bottle set.
Topaz bearing Rhyolite, from Topaz Mountain, Utah.
This stuff is just amazing. High in Silica and Alumina, it also speckled with Topaz gemstones (mostly very small in scale – this sample is exceptional). It’s features in all of my Basalt/Rhyolite glazes, which I’ve named Fiske Lava Oilspot. The recipe? 3 Parts Rhyolite, 1 Part Basalt. See the small test tiles for what it looks like fired by itself.
Granite from Cook Canyon, Near Willard, Utah
Plain old granite. It turns out this stuff makes a beautiful range of glazes completely by itself. Its used as a glaze on the 2 Tiered Granite Slab piece, and it’s used in the matte black glaze on the set of 4 cups on the smaller granite base. The matte black comes from an addition of 1 part Hematie (Iron Ore) to 4 parts Granite.
Vesicular Basalt (Lava Rock) from Sid Butte, Idaho.
The local geology abounds with basalt of all flavors, but compositionally, they’re all relatively similar – at least as far as my glazes and firing process is concerned. This specific variety got me started on researching basalt glazes, and when I started using the lava oilspot glazes I incorporated local Utah varieties from outflows near Delta, Utah, as well as roadcuts off in Box Elder County, Utah. It accounts for the rich reds and oranges in my Lava Oilspot Glazes.
Iridescent Hematite from near Eureka, Utah
This spectacular sample survived my hammer and the studio milling equipment. It’s nearly pure iron. Less spectacular examples have been incorporated into all of the Iridescent Hare’s Fur Glazes and Black Oilspot Glazes, as well as the Black Granite Cup Set.
A glaze is nothing more than a glass-like coating fused to a ceramic surface by heat.
Nearly any rock or mineral can be utilized in a glaze. Most ceramics studies are stocked with materials that have been mined and commercially prepared for consistency and ease of use. But you can easily dig up anything and see what happens, sometimes it’s not at all useful for ceramics, but sometimes it is – and these are wholly unique to the place you get them from.
The first thing I do when I bring back a sample (1a,1b) to my studio is to use my trusty sledge hammer to break a small sample into pea-sized gravel. This gravel then goes straight into a small bowl (1c), and straight into a kiln. After this initial firing to 1250C (2350F – that’s HOT!), I can usually get a very good idea of what a sample might do in glazes. I might not have any idea what a material is – but after firing it, you can tell how it will behave at standard ceramic temperatures. Sometimes one gets lucky (as was the case with the granite) and ends up with a material that makes a perfectly acceptable ceramic glaze all by itself. Usually though, it takes some testing to find out how to fire specific materials.
Because the atmosphere in the kiln has an effect on the color of the glazes it’s useful to do initial melt tests in an oxidized (regular atmosphere) firing (2a) as well as firing the material in a reduction (excess fuel, reduced oxygen atmosphere) (2b) The firing atmosphere changes the color of the clay and the material quite significantly. My Oilspot glazes rely on regular atmosphere firing conditions for the phenomena of oilspots to occur. Celadon glazes, on the other hand, require reduced oxygen conditions for the iron to change from it’s oxidized (rust!) red color, to a reduced black color. These tiny black iron molecules are what make my celadon glazes appear blue.
(3) is a sample of granite melted at 1250C. Right away I could tell this was going to be a great material to work with. With no additions it’s good to apply directly to pots as soon as it’s milled. The liquid in (6b) is pure granite glaze.
(4) is a sample of Black Schist melted at 1250C. You can see that this sample needs to be amended or mixed with another material to make a useful ceramic glaze.
It can be useful to fire samples at lower temperatures to find out when exactly they start to melt and fuse to a clay surface. (5) is a sample of basalt fired to about 1000C, which was hot enough to affect the iron in the basalt, but not enough to melt the bulk of the other minerals present.
After establishing that a rock is going to be useful, it’s time to begin preparing it for use as a glaze. A 15 pound (bowling ball sized) hunk of rock will provide about 5 gallons of glaze. 5 Gallon buckets are a standard in most studios, and I used about 5 gallons worth of glaze to finish all of the black and Hare’s Fur Oilspot pieces in this exhibition. Making a rock a glaze material is a rather simple process of using a hammer or milling machine to crush rocks into fine powder. My favorite way to do this is to use a ball-mill, which is essentially a heavy-duty rock tumbler. To a tightly sealed metal jar you add: 3 Parts material, 3 parts water, 4 parts porcelain balls(6a). Put this jar on a machine that spins, and in about 24 hours it does the job that takes Mother Nature millions of years (who is constantly turning mountains into clay). The mill works by mechanically mixing and breaking the material into finer and finer pieces. Your done when the material (6b) passes through a fine mesh strainer. You can then dry it out and use it like any other ceramic raw material (6c) or you can dip or apply it directly onto pottery or test tiles (7).
Basalt, Iridescence, and the Firing Process
In the course of poking around and looking at rocks in Idaho, one particular sample of basalt caught my attention. The iridescent vesicular basalt on the right an example of what I picked up. I became very interested in the question of why this material had a bluish iridescent metallic sheen – and why the rocks next to it didn’t. I speculated that since some ceramic glazes can be fired in ways to make them turn iridescent (raku firing, for example) it might just be the case that I could fire basalt in a way that it would turn out with the same lustrous metallic surface.
I then set about testing my theory. I started by making nine 8” stoneware tiles, which would all have the same application of the same ground basalt. I then designed a series of firing schedules where I would change two variables: 1.) Atmospheric Conditions Inside The Kiln – specifically whether I would keep the kiln in oxidized natural atmosphere or whether I would reduce the available oxygen by firing in a gas rich environment. 2.) Cooling Speed. Of particular importance in the color of ceramic surfaces is the speed at which a molten, melted glaze cools down and crystallizes when the burners are shut off and the kiln returns to room temperature. In this series of firings, I took careful notes, paying very close attention to both the atmosphere in the kiln and the rate at which I allowed the kiln to drop in temperature.
I did indeed find that I could reproduce a metallic iridescent blue sheen from basalt lava rock (see the tile in the middle). The trick was to fire the kiln normally, and then cool the kiln very rapidly to about 1000C (which is the stage in which the viscous, molten material starts to harden) and then hold the kiln at a steady temperature in a reduced oxygen environment for an hour or two, then begin a very slow -2 degree per minute drop in the same reduced oxygen environment until the glaze had completely solidified around 700C.
What I learned through this series of experiments is that the iron in basalt and other iron rich glazes is greatly influenced by rate of cooling and atmosphere. By manipulating the atmosphere and rate of cooling, I could affect the colors of glazes – thereby producing unexpected surfaces and colors. It was this research that then led me to develop all of the variations found in both of the installation pieces in this show. The glazes are the same- but the firing processes are very different.
Rhyolite/Basalt Glaze (Lava Oilspot Glaze)
While it was exciting to work with basalt as a material, in most cases it left something to be desired as a functional, utilitarian ceramic surface. It had the tendency to run completely off the pots, and it often had a blistered, matte surface. Very few glazes in ceramics contain one singular material, sometimes a glaze recipe can call for as many as 20 different materials. I needed to add something to my basalt to make it more functional, and a breakthrough came after my Mineralogy class fieldtrip to Topaz Mountain, in Southwest Utah where I collected a 5 gallon bucket of Rhyolite gravel.
Rhyolite, which is another volcanic rock and it lies on the on the other end of the spectrum of igneous rocks. Rather than being high in Iron and Magnesium like Basalt, Rhyolite is very high in Silica and Alumina. In glaze chemistry, you can think about Alumina as the opposite of a flux. Rather than lowering the melting temperature, it raises it. Referring back to the local materials in this show, you might notice that I’m using Dolomite and Travertine to increase the melting and moving of glazes in the kiln. Conversely, I’m using Rhyolite to stiffen and slow down the melting of the glazes.
Often the first experiment to do with a prepared local material is to do what’s called a line blend. The five pieces on the shelf below are what are called test tiles, because it’s often not feasible to devote a piece of pottery to a glaze you don’t know much about. In a line blend, you move in steps from one material to another. The tiles below represent a progression from 100% Basalt , to 75:25, to 50:50, to 25:75, then to 100% Rhyolite. In other words, on one end of the line you have one material, in the middle you have a perfect mix of the two, and on the other end of the line you have the other material. You can move in big steps, which takes less time, or you can move incrementally. The point then, for a line blend is to help you narrow in on a nice proportion, and sometimes a second series will help you narrow it down further – say the 50:50 and the 75:25 test tiles look very promising, you might then decide to do a second progression from 50:50, 55:45, 60:40, 65:35, 70:30, and then 75:25. The possibilities are endless, and you can add in a third and fourth material to the blends and very quickly use up a lot of test tiles and explore a lot of variations. I’ve also included some of my notes, which cover only a few of the thousands and thousands of glaze tests I’ve mixed and fired.
I was lucky though and the first line blend yielded my Lava Oilspot Glaze. It’s 1 part Basalt, 3 parts Rhyolite. A very simple glaze recipe for sure. But remembering also that the firing and cooling have a great deal of influence on the finished surface, I’ve spent the last year investigating the possible variables on this very simple recipe with very, very complicated firing and cooling processes. The results of which are the 16 Rhyolite/Basalt Bowls, all of which were made from the 1:3 recipe, but fired in very different kiln cycles. I’ve also included some examples of several of my firing cycles.
The Scanning Electron Microscope
My research with the SEM on campus began with a generous scholarship from the Office of Research and Graduate Studies. With my membership to the Microscopy Core Facility, I was able to take my own samples and prepare them for analysis on a state of the art Quanta Scanning Electron Microscope. Fen-Ann Shen, who oversees the SEM was a patient teacher, and she taught me first how to use the equipment on calibration samples, and then later, to prepare my own ceramics and begin looking at the surfaces and structures on the nano-scale.
It should be said that an SEM is not an optical microscope – and by that I mean it’s not what you’d normally imagine a microscope to be, namely, a tabletop instrument with two lenses that you look in. While optical microscopes are useful for looking at surfaces, magnification maxes out at about 800-1000 magnification. An SEM, on the other hand, operates on the principal of firing a concentrated beam of electrons at a sample and analyzing the electrons as they bounce back (backscattered). Scanning is in the name because this beam moves across the surface of the sample, building an image as the resulting information is compiled. While an optical microscope maxes out at around 1000x, the SEM at USU is capable of 300,000x magnification. In effect, you can look at nano-particles in high resolution. That’s 1/1,000,000,000 of a meter! A human hair is about 100,000 nano-meters in diameter. It’s therefore quite easy to get completely lost in an area smaller than an eighth of an inch.
The images in this exhibition represent some of the most exciting surface features and topographies from my own glaze. To date I’ve only looked at 3 glazes, and all of them are in this exhibition. I’ve included the actual samples themselves, which are mostly broken shards and chips of glaze. As I began to learn more about the equipment and preparation, I began to make samples specifically to fit on the small conductive sample mounts.
I might also add that these images represent the very beginning (I’ve spent less than 20 hours looking at my glazes) of what I see as a very exciting chapter in my exploration of materials and glazes. Most published images are the result of hundreds, if not thousands of hours spent in front of the monitor, patiently waiting for scans to complete. I was lucky, then, to capture the images I did, and I’m very excited to continue this research in the future.
Fiske Hare’s Fur 1
Fiske Hare’s Fur 2
Fiske Hare’s Fur 3
Lava Os 1
Lava Os 2
Lava Os 3
A special thanks to The Office of Research and Graduate Studies along with The Caine College of the Arts for providing me with an incredible ART-STEM fellowship – without this funding, it wouldn’t have been possible for me to devote all of my time and energy to focus on my research. My fellowship has opened doors to departments across campus, and has facilitated a great amount of collaboration and research outside of the Department of Art and Design.
Thanks to the USU Ceramics Faculty for giving me a long leash to play around and melt things and make messes – and thanks also for reigning me in when I got carried away and always reminding me that I can’t fire kilns without actual work. Without craftsmanship there is no concept.
Thanks to my Graduate Advisory Committee for helping me decide what I should be doing, not what I could be doing. Thanks also to John Shervais and the Geology Department for help with my projects and insight into material science.
Thanks to Kenzi Lowry for help with the graphic design of my postcards and posters and helping me format the SEM images and get them ready for printing. Thanks for working under impossible deadlines and tolerating my constant adjustments and second guesses and indecisiveness.
Thanks to Fen-Ann Shen for training me on the use of the Scanning Electron Microscope and helping me figure out how to prepare and analyze my ceramic samples. I look forward to investigating more materials in the Microscopy Core Facility.
Thanks to Nicholas Gialanella for providing me access to the printers in Photography and working with me to produce the SEM images.
Thanks to Ryoichi Suzuki, who had a huge influence on my thinking about the possibilities of stone and for giving me access to the sculpture facilities.
Thanks to Miles Howell for his help in preparing and roughing out the stone bases – he got done in hours what would have taken me days!
Thanks to all of my graduate and undergraduate colleagues in Ceramics, for putting up with my messes and firings, and for inspiration and camraderie. Also, a shout out to the corner for the tough love.
A final thanks to The Department of Art and Design. Laura, Becky, Tori, and Janet, you’ve all been incredibly helpful and supportive not just in the run up to this show, but throughout my time at USU. Thank you!
More local Basalt. Here used as colorant in high fire celadon glazes. On the top left, the raw material which was collected from various places throughout Idaho and Utah (and all mixed together), bottom left the homogenous, calcined, milled, sieved, and dried material ready for glaze.
In this set the basalt is supplying the iron necessary for that timeless celadon blue. Its also bringing significant additions of magnesium and calcium to the recipe. The % of basalt here ranges from 0 to 10% in 2.5% steps – applied to a dark stoneware and porcelain tiles.
This series were fired in a very fast and simple cone 10 reduction firing with a very basic reduction cool. 6 hours start to finish, in a small fiber test kiln — Heavy body redux for 30 min @ ^012-^08, then light redux to ^6, then a medium redux to ^10. At soft cone 11 I crash cooled a few hundred degrees, turned the air and gas down, dampered in, and put the kiln into about a -4°/minute cool, periodically opening the door to quickly crash cool -30 or -50 degrees until 1400, then shutting everything off. In some cases reduction cooling will effect the color and quality of the glazes significantly, but here it only effected the stoneware – keeping the iron oxide on the surface in its black reduced form. A good reduction firing will yield these glaze colors with no special effort cooling – here the RC was strictly for a darker stoneware color.
Fiske’s Tichane Chun Custer Feldspar 48 Silica 31 Calcium Carb. 20 Bone Ash 1 (Iron Oxide 1.5)
— A range .5 to 3% Iron Oxide gives a similar spectrum of blue as the basalt does here – different flavors of Iron bearing materials yield different flavors of glaze, obviously. I’ve tried probably more than 50 kinds of iron over the years – try what you have and figure out what flavor you like best!
Fiske’s (Pinnell Clear) PC Celadon Custer Feldspar 25 Grolleg Kaolin 20 Calcium Carb. 20 Silica 35 (Spanish Iron Oxide .85)
Basalt from 0-10%
Mn Dark Stoneware with 10% Basalt Chun Left, 10% Basalt Celadon Right
Hello Again! It’s been quite some time since my last post. Gotta thank those of you who have contacted me with interest and suggestions! With so many summer projects and school stuff, it’s been very difficult to put my full efforts into any one thing… but life is what happens while you’re making plans. Anyways, enough with the excuses.
Over the summer I had the time and energy to figure out an acceptable firing schedule in our new Blaauw kilns. For as much as I love their sleek and sexy design, computer controllers, and top of the line hardware… you can’t look in the damn things while they’re firing. This poses several challenges for control freak oil spotters. Usually, the idea is to firein complete and total oxidation, going slowly through cone 7,8,and 9 to allow thermally reducing iron to bubble up through the glaze and cause the surface to crater or foam. By carefully monitoring the situation inside the kiln, and by pulling out glazed pull rings, the firer can increase the temperature slowly and fire until the glazes have significantly ‘healed over’. This isn’t really an option, so as a result a much more empirical approach was needed to find a good fit.
After 5 firings, I settled on a more or less acceptable firing schedule (the way this programming works is that the kiln starts at 0, take 1:30 to get to 200C, then 2:30 to get to 700C, etc). In Celcius;
time_temp 00:00 5
time_temp 01:30 200
time_temp 02:30 700
time_temp 03:00 1115
time_temp 02:00 1190
time_temp 02:30 1230
time_temp 02:30 1253
time_temp 02:00 1000
time_temp 02:00 500
time_temp 02:00 300
time_temp 02:00 50
time_temp 04:00 50
Once that was established, I began with some of my favorite tiles from my initial 2 rounds of oilspot base glaze recipes. My favorites:
NoCo OS: (NC)
K200 Feldspar 57.3
200m Silica 24.2
Spanish FeOx 10
Candace Black: (CB)
K200 Feldspar 60
200m Silica 20
Spanish FeOx 8
Cobalt Carb 5
Local Black Dolomite 10
Red Iron 8
Fake Mashiko: (FM)
Calcined Redart 35
Bone Ash .5
Red Iron 4
With these base glazes I began mixing, blending, and layering, and combining glazes with dipped, poured, and sprayed application. On a whim I decided to experiment with some of my manganese saturate glazes, and that’s when things started to get really interesting. There is admittedly one glaze in particular that I’m not sharing, but with a little diligence and some wet blending, a seriously motivated glaze experimenter can discover this glaze by looking at my old posting on my OSII series. Blend them all in 50/50 proportions and you’ll get the elusive but beautiful GF glaze. Hell, it might even be on my blog somewhere. That’s all I’m saying for now – I’d hate to rob anyone of the learning experience… Hah! =)
Recently I was contacted by the British potter Allen Richards who has done some pretty extensive research into lustrous gold glazes. He suggested that I try small additions of Vanadium Pentoxide. These glazes feature 2 amended manganese saturate glazes in combinations with the usual oilspot suspects.
Here are some videos of some of my latest results. None of these particular tiles have Vanadium pentoxide. As time goes by I’ll try to annotate the combinations MS corresponds to Manganese Saturate.
Started out with Kamada Koji’s big bang glaze in mind. I’ve been completely obsessed with all glazes iridescent for some time now. This is my favorite variation to date… but still too subtle and elusive. Closer than I was, but still a lot of room for improvement.
This is the glaze I’m calling Fiske GoldFur – which came from a blend of some variations on a fake Mashiko with calcined redart, and a variation of a Britt oilspot with local black dolomite.
The center action of the GoldFur piece.
Some combination of some variations of variations.
Started out with Kamada Koji’s big bang glaze in mind. I’ve been completely obsessed with all glazes iridescent for some time now. This is my favorite variation to date… but still too subtle and elusive. Closer than I was, but still a lot of room for improvement.
Another angle of the GoldFur piece. Getting closer and closer to something completely new and completely incredible.
Back in the studio after a great trip over to Telluride, CO via Moab, UT. You better believe I scooped up some of this clay, ball-milled it, and made a slip. I also packed the jeep with a load of rocks and shit. More on that as the story develops!
Manganese crystalline glazes (high alkali, silica, and alumina) are usually created by saturating a feldspathic glaze with between 15-60% manganese dioxide. During the cooling cycle, manganese precipitates out of the molten glaze and crystallizes on the surface, producing lustrous, satiny surfaces.
UNDERSTATEMENT: Manganese Dioxide is extremely hazardous to your health!!!
Breathing in Manganese dust when mixing these glazes or breathing the off-gassing vapor when firing WILL GIVE YOU PARKINSONS-LIKE SYMPTOMS BEFORE ULTIMATELY KILLING YOU, PAINFULLY. HEAVY GLOVES, DUST MASKS, AND VENTILLATION ARE CRITICAL.
There is a long history of lustrous, metallic glazes. The first examples are thought to be from the early ninth century in an around what is modern day Iraq. Archeological evidence suggests that early examples originated from Mesopotamia in Fustat, which was then the capitol or Egypt. The oldest surviving examples were often multi-colored stains and iridescent sheens derived from copper and silver compounds. These compounds were usually manufactured by dissolving coins into acids and then mixing the resulting solution with earthenware clay. This mixture was then calcined and then finely ground. The resulting pigment was then mixed with a carrier (usually lavender oil) and applied to lead or tin glazed pots and re-fired to dull red heat. The pots were then held in an extremely smoky reduction environment at various temperatures and lengths of time, which resulted in surfaces ranging from olive-green, brown, amber, orange, yellow, crimson, and a very dark red which was sometimes so dark as to look almost black.
Although the history and development of reduced-pigment lusters is long and storied, it was a more or less consistent sequence. It isn’t until the 19th century that one starts to find examples of resinate lusters. This resulted in the development of materials almost identical to modern ‘liquid gold’ and ‘platinum’ lusters. In Europe in the 1870s a revival in the technology and development of luster glazes saw a further refinement of reduced glaze lusters, most notably in the studios of William De Morgan, Massier, Kähler, and Zsolnay. This notable shift was the result of the use of higher firing clays, which French ceramicist Louis Franchet believed could offer the complete range of earlier pigment-lusters, but without a lot of the trouble. Aside from the obvious temperature differences, the main difference between pigment and reduced glazes is that glaze lusters are generally less subtle, less mellow, and offers a wider, more brilliant range of color.
I began research on this project in an attempt to find a brilliant, iridescent glaze similar to Zsolnay’s famous Eosin glaze, which has a very obvious bright reflective rainbow iridescent quality. Initial research suggested that Zsolnay’s effects were the result of the thin application of copper, silver or bismuth to a pre-fired glaze – firing to fusion point, and then reducing the kiln atmosphere during the cooling cycle. This method is documented extensively in Greg Daly’s book Lustre. Having had some glimmers of success with iron saturate glazes in reduction cooling environments, I proposed a solution that did not; 1.) involve expensive silver or bismuth oxides, or caustic salts such as stannous chloride or copper sulfate, and 2.) involve a postfiring or overly exotic and difficult to repeat firing schedule. In the end, a satisfactory solution was some combination of feldspathic glazes with 30-60% Manganese Dioxide, following closely in the steps of David Shaner, Lucie Rie, Hans Coper, John Tilton, and historical Rockingham ware.
Reduced-pigment luster. Nearly all historical luster made before 1800 fits in this category. The result of calcining copper, silver, and bismuth oxides with earthenware or laterite clays, and applying the resulting mixture to a maturely fired lead or tin glaze surface. The piece is then refired and held in heavy reduction at dull red heat allowing for a thin layer or metallic oxide to fuse with the surface of the glaze. After the firing, the earthenware is wiped away, revealing a nano-thick layer of iridescent metal.
Resinate luster. Usually made with dissolved gold, platinum, or other noble metals and suspended in an organic binder. Generally fired to a low temperature, with the organic compounds burning out and fluxing a thin, even layer of metallic oxides with the surface of the work. Developed around 1800, very common in industry, very toxic.
Reduced Glaze Luster. Generally higher porcelain and stoneware temperature. Usually cover the entire surface of a form. Relies on metallic saturated glazes precipitating out thin layers of reduced metallic oxides which deposit in a thin layer on the top of the glaze. Generally more brilliant and operate across a wider spectrum of interrupted light.
Materials: I found that nearly all of my iridescent surfaces contained some percentage of manganese. The exception is a traditional Tenmoku glaze fired in standard reduction, and then ‘struck’ at 1840F for 1:20-2:00 hours. Strike firing, or striking the kiln is a glass term which refers to increasing the fuel supply and thus creating a reducing atmosphere around 1800F. Initial tests suggested that manganese saturated glazes promoted richer iridescent surfaces regardless of a strike firing. Additions of other oxides were often counterproductive to glossy surfaces and generally resulted in unpleasant black, rough surfaces. Copper, Iron, Chrome, Nickle, and Cobalt were all tested alone and in conjunction from .1 -> 20%. The character of the underlying glass matrix of was usually beer bottle brown, so I tested extensively to change the color of the glass without effecting the iridescent surface – to date I still don’t have a simple solution to this problem. Granular Manganese seemed to produce brighter colors as well as promoting streaking ‘hares-fur’ effects in faster cooling, and acting as ‘seeds’ to crystal formation on slower cooling cycles. My ideal concentration of granular manganese was 2% and fine manganese dioxide at about 27%.
Most recipes called for 50-70% feldspar, and after testing all of the available feldspars, I found that Nepheline syenite promoted a much smoother, regular iridescence. Custer feldspar promoted iridescence across a wider spectrum, but promoted intense crystallization as to appear almost pixellated. Kona f4 promoted a more matte, golden green/purple sheen. Other feldspars promoted a lustrous brown glass with varying degrees of light to moderate iridescence.
The addition of silica promoted a lightening of the glass matrix, as well as a sugary, semi- shiny sparkling satin luster. Silica beyond 15% eliminated iridescence. Alumina additions to the glaze produced a semi-matt honey colored glaze.
I found that the clay body had a huge impact on the color and quality of the iridescence. The most successful clay bodies were grolleg based porcelains, with only the highest percentages of manganese based glaze recipes showing even the slightest luster on stoneware recipes.
Finally, glaze thickness was perhaps the most critical aspect of obtaining iridescence at high temperature. This was complicated as these glazes are extremely runny. Even slight overfiring resulted in glazes running off the pot. There was a need to find a balance between adding clay and silica to the feldspar and manganese without diluting the concentration of available metal oxides and feldspar. It was also extremely difficult to apply these glazes consistently, and fire them in such a way as to reach maturity without overfiring.
Firing: All tests were fired in high temperature gas kilns. I usually fired to 1260C, or Orton cone 10. A majority of my testing was in standard cone 10 reduction firing, with a 1 hour body reduction at cone 012-> cone 08, and a 6-10 hour firing from cone 08-> cone 10. Recipes with 15% copper produced a striking gold color in oxidation environments, and glazes in oxidation firings bubbled and boiled up between cone 7-9, which suggests a similar thermal reduction similar to oil spot glazes.
Cooling: Most of my firings were in small soft brick or fiber kilns, so the possibility of extended cooling cycles was limited. I found that crash cooling seemed to promote smoother, less brilliant surfaces, and a moderately fast cool was ideal in creating a balance between bright color and reasonably smooth surface. Longer cooling promoted larger crystals to a point, and excessively long cooling cycles promoted a matte surface. Reduction cooling remains an exciting possibility which mostly extended beyond the scope of my research. A very interested mottled crystal growth was observed on bottle forms cooled with a 3 hour reduction hold at 1840F.
 Caiger-Smith, Alan. Lustre Pottery: Technique, Tradition, and Innovation in Islam and the Western World. London: Faber and Faber, 1985. Print. Pg. 21
 Caiger-Smith, 1985, Pg. 177
 “Iridescence in Lepidoptera”. Photonics in Nature (originally in Physics Review). University of Exeter. September 1998. Retrieved April 27, 2012.
Britt, John. The Complete Guide to High-fire Glazes: Glazing & Firing at Cone 10. New York: Lark, 2004. Print.
Caiger-Smith, Alan. Lustre Pottery: Technique, Tradition, and Innovation in Islam and the Western World. London: Faber and Faber, 1985. Print.Pg 149
Conrad, John W. Black Pearl and Other Saturated Metallic Glazes. Santa Ana, CA: Falcon Division of Aardvark Clay, 2010. Print.
Currie, Ian. Revealing Glazes Using the Grid Method. Australia: Bootstrap, 2000. Print.
Daly, Greg. Lustre. London: A. & C. Black, 2012. Print.pg. 131
Hamer, Frank, and Janet Hamer. The Potter’s Dictionary of Materials and Techniques. London: & C Black, 1991. Print.