glazenerd

and that is how you know it is sodium bentonite: it swelled, became gelatinous. Calcium bentonite does not have that same reaction. Tom

Tina: This test tells me a lot: at 10min. indicates your clay has very little fine particles. At 1hr.15 min it is completely separated. Your clay is mostly comprised of 2+ micron particles; which is large in the world of clay. It also tells me your clay has no appreciable amounts of sodium, potassium, or calcium. I have tested wild clay that has stayed suspended for several days because of the feldspar content and sub-micron particle size. Run the same test using your bentonite: see how it goes. Google two things and check to see if they are available to you. 1. potassium fertilizer; which should show up at local farm or garden shops. If they have it: what is the potassium content, and how much phosphates? 2. Fullers Earth: which is fairly common in the Asian markets. Given the temp range you are firing to: Fullers Earth would be more beneficial for many reasons. Much easier for North American, European, and Australian potters to fix things because we have easy access to many different materials. There are many areas that availability is limited: if any exist at all. Tom

Caveman: Lets start with pictures of your unprocessed clay. I am somewhat familiar with the local clay in Ohio: iron disulfide (pyrite) is the common iron bearing clay. Having a mix of color in a single clay vein is not that uncommon. The red/orange is obviously iron bearing clay: the white color is most likely ball clay: there are no kaolin deposits in Ohio that I am aware of. Grey color in an indication of sulfides, given your location. Much of clay in Ohio has some levels of sulfides because of their proximity to coal seams. Grey can also be an indication of organics: was this clay sourced in areas of heavy vegetation? Post some pics, and that will give me some general sense of what you found. Tom

Tina: When deciding what to add or remove in a clay body; it comes down to application and firing technique. 1. Functional or non-functional. Functional has specific limits, non-functional has none. 2. Firing- pit, kiln, raku: different firing techniques create their own demands on clay. So before I can answer: how do you plan on firing it? What temperature (cone) do you plan on firing it to? Are you making functional or non-functional pieces. Tom

Oklahoma "wild" hematite clay at cone 6- unglazed.

and by the way: like glaze- plenty of failed recipes as well. Tom

Tina: Your new tan clay is medium + plasticity. Common for clay to be smooth on one side, and textured on the other when you first start rolling it out. Most of the cracks are on the edges: which is just stress from being rolled. It could use some help; but not much. You can start with 1% bentonite additions. I did not bring up the new clay in my other post, to avoid confusion. Upon viewing it; my initial thought was to use it in part with your reddish clay to help even out PSD (particle size distribution). Common to blend clay to help with plasticity, working properties, and fired properties. You made the comment. that both the clay and bentonite had the same volume. Do not be deceived by that: bentonite is ultra fine particle, and the trapped air makes up a large part of the volume. Tom

Tina: greenish clay typically indicates calcium and/or magnesium is present. In some cases; calcium/ iron. Bentonite can absorb 15 times its weight in water: so it will swell when water is added. Yes, the formula I gave you is very rich in plasticizers; I did so with intent. Note: when you post pics: number them, so the discussion is easier to follow. Also, do not throw away this test batch regardless of outcome. I plan on reusing it. The weird smell may be organics. Tom

Hi Tina: Lets skip down to the pictures where you drop in the squares of your clay. "pieces of your failed attempt." Notice on the right (with baking soda) the clay begins to dissolve as soon as it hits the water. In the next picture: the plain water (left) is partially dissolved, but not fully dispersed. On the right (baking soda), the piece is fully dissolved, AND fully dispersed. The next pic ( 1 hour, water only) the clay is still not fully dispersed, and there is cording present. (cording means visible lines of color and distinct lines in the clay). 4th pic (one hour with baking soda) the clay is completely dispersed, no cording. 5th picture ( I stirred both and let them sink). the left has completely separated between material and water. The right has separated into three layers; each layer being (large particles on bottom, medium particles center, and fine particles on top (looks like colored water). After reviewing: you have three points. The cementing problem is medium; I have seen worse. 2. The clay lacks any naturally occurring feldspar ( sodium, potassium, nor any calcium) 3. The particle distribution is mostly larger. Lets see how to word this without being too techie. Feldspar ( sodium and potassium) along with calcium create a negative charge in the clay/ and water. When that negative charge is absent; clay forms clumps even when wet (flocculation, and when severe- cementing). Feldspars are alkaline, and alkalinity creates a negative charge; which repels adjoining particles; or what potters call plasticity. Plasticity is a function of deflocculation. That same negative charge ( or lack thereof) also plays a role in drying. A strong positive charge ( your clay currently) will add to cracking when it dries; which is further compounded by larger clay particles. So to correct it; you have to create alkalinity ( which is done by adding feldspar or calcium), and by the addition of fine particle clay. You have bentonite now: do you have access to feldspar? sodium, potassium, or calcium? Take a pint of water, and add 1/4 cup of baking soda (stir well). Add 8-10 pieces of your "failed experiment clay chunks"; and let them dissolve completely ( about an hour). Stir it well, then add 2 tablespoons of bentonite ( little at a time, stir between each addition). Let it sit overnight, and pour off any excess water that comes to the top. Empty it out on a board or table (something flat) and spread it out. Let it dry down to a "clay consistency". Then just roll it out as a flat slab and let it dry. All we are checking is cracking- nothing more. Tom

Hi Terra: Moly crystals as they are more commonly known as fall under the Crystalline Glaze category. Molys are complicated, and there is a step learning curve in learning how to develop the glaze, and firing them. Like crystalline; the glaze is bought up to a peak temperature: then lowered to a specific temp and held for several hours. (Called a ramp hold). I have been firing crystalline for awhile now; and still pull my hair out when firing molys. So be forewarned: you are about to dive down a very deep rabbit hole. If your kiln does not have a programmable controller, and if your kiln does not hit cone 10: no point in trying. You will spend several months educating yourself, and a few more months of trial and error before you get these dialed in. You will not find information on this site, and as you have already found out- or find information anywhere. Crystalliziers as they refer to themselves, closely guard their favorite recipes and firing schedules. I do know where we happen to hang out: Facebook- Working Crystalliers. Tom.

It has been close to a decade since I bought any commercial clay. Years ago, I put the same crystalline glaze on five different commercial porcelain bodies, and got five different results. That single incident sparked my curiosity about clay formulation; which turned into an obsession for awhile. I do crystalline tile almost exclusively; and every commercial porcelain body I tried- warped. From that, I developed a crystalline body that actually promotes crystalline growth; instead of hindering it. I developed a porcelain tile body that I roll out on 2 x4 x 1/2" luan, and let it sit until it pops off on its own. My days of flipping, weighting, and spending hours trying to prevent warping are long over. Few years back I developed an extensive line of colored porcelain: which I use from time to time. Local supplier wanted me to distribute it; but not really had the time to get that involved. A shoulder injury from a few years back has also hindered that endeavor. My bigger interest of late has been collecting and processing locally sourced clay. It holds my interest; breaking it down and figuring out how to make it a workable body. I have samples sent to me from across the US, and on rare occasion- other countries. Rather fascinating to see the results from iron disulfide, hematite, and magnetite samples. Still toying with the idea of bringing back a semi-load of hematite clay from NE Oklahoma- best looking cone 6 results I have ever seen. I have been contacted by potters across the globe for in depth discussions on how to fix their naturally sourced clay issues. The most complicated puzzle was sub-tropical laterite from India; took awhile to find the solution. (43% total iron/alumina content). Collecting and processing natural clay is more popular than most realize; but it is not a topic that is widely discussed here. A few months back another interest has taken center stage in my life: so clay may have to take a back seat for awhile. Nerd -- the pic below is Oklahoma hematite.

Tim: Temper is well known among those who collect and process natural clay; and those who fire primitive pottery. Temper is added for malleability; in lieu of known clay formulation methods. Grog is added to increase green or fired strength, or it can be added to control warping, and or increase thermal shock properties. Hardpanning is more associated with glaze than clay; although it can happen in soil deposits if conditions are right. Processing natural clay rarely comes up on this forum: although it has gained popularity in the last decade. Tom

Hi Tina: Been following, going through the information you posted. Sand additions are called "temper" in our clay world: first used in native pottery, and later by the brick industry to make clay more suitable for pressing. While sand added to the problem; it is not the problem. You soaked your clay for several days and still had lumps: this indicates the real problem- it is called "cementing." Cementing is a severe form of flocculation; caused by high iron/alumina levels that create a strong positive charge in the clay which makes it resistant to uniform dispersion of particles: which in turn results in delamination, sheering, and cracking. It requires more than adding plasticizers to the clay: you have to break the strong positive charge that creates this problem. Acidity creates flocculation and alkalinity creates deflocculation. Now lets put that theorem to the test: 1. Find two 1" hard clumps of clay. 2. Fill 2 glasses, bowls, dishes with a 1/2 cup of tap water. 3. Add 1/8 teaspoon of sodum or potassium feldspar to just one glass (leave the other plain tap water). If you do not have feldpsar; then add 1/8 teaspoon of baking soda. Stir it well to disperse the powder. 4. Drop one chunk of clay into each glass/bowl. (Do not stir or agitate.) Let it stand for 30 minutes. 5. Use your finger or spoon to see if the clay chunk has dissolved on its own. If my theorem is correct: then the chunk of clay in the glass with the feldspar/baking soda will have dissolved on its own. Feldspars/ baking soda create alkalinity; which in turn creates a negative charge in the water; which in turn neutralizes the positive charge that created the "cementing" property. Tom

"Sticky" is an indication that organics are present. A particular kind of humus called Ord is commonly found in natural clay. Ord is many times more plastic than bentonite: which makes clay "sticky." Have you dissolved any in water? If so, any dark particles float to the top? Without pics, I have to assume your "dark" description means dark gray? If so, most likely you have magnetite (iron) in your clay. Magnetite will fire a terra cotta color at cone 06, and turn deep brown at cone 6. Iron disulfide (pyrite) also follows that color transformation. Hematite (iron) will keep more of its terra cotta color at cone 6. Sheering in this case is most likely a lack of fine particle clay: which you indicated it has a sandy feeling. Add 20% OM4 or equal ball clay, and see if the sheering improves. Remember to let is sit 5-7 days after you mix it in; takes a bit for plasticity to develop. Yes, a sheen can be an indication of vitrification: but it can also occur on the surface from out gassing of inorganic materials. I am making the assumption that is magnetite from your color description. The most common iron source in the USA is iron disulfide (pyrite); which on occasion can be a dark grwy color pending organic levels or other minerals in the deposit. If you fire iron disulfide quickly, you will get a sheen from sulfur off gassing. Without pics, sort of a guessing game at this point. Tom

It has been close to a decade since I have purchased pre-mixed clay. I mix my own blends, using recipes I developed. I use a PP SS30 to mix. I have an electric cement mixer that holds 150 lbs of dry materials. I load it, let it mix for 15-20 minutes, and scoop out dry blend as needed. I mix outside to keep the dust down. I mix dry materials and water in a 3 gal bucket to create a heavy slurry: I do not pour water directly into the mixing chamber. I fill the chamber completely with dry mix, and then begin adding slurry. Once I get close, deair, then pug about 12” of clay, throw it back into the chamber to remix. This assures the chamber is filled with solid, well mixed clay. I mix mostly porcelain, an occasional stoneware; and done a few loads of colored porcelain. More recently, mixed several loads of locally harvested clay. I have marks on my table to lay pugs on: these marks allow me to cut 1-2-3-5 lb balls without weighing. Tom

Babs- sorry for the delayed response- not been around much as of late. It’s been 10+ years since I dug around on light/dark rutile. I do recall bisq firing sample up to 1000C- with very little changes. T

Dick: Potassium (USA) historically mined in New Mexico (potassium chloride) and Utah (potassium/magnesium). More recently, in Nevada: in proximity to boron/borates. Is Pacer running their own mines, or contractually purchasing from mines? Given the fluidity: would be looking hard at boron (ulexite) contamination. Tom

Dexter: perhaps I should explain the chemistry behind charcoal. The briquettes become granular when you crush them- 1/16, 1/8, 1/4": which acts as the grog to give this simple mix the strength to form. This is the reason grog, straw, and hair is not necessary. Rocket stoves are typically 1 1/2" thick: self supporting when formed. Oven ware bodies are primarily ball clay; that utilize low expansion fluxes (lithia/magnesium), not potassium/sodium used in cone 3 and up. Magnesium has a low melting point as well. Secondly, unmelted silica is highly expansive: so oven ware (and raku) swap out pyrophyllite for silica additions to help control expansion. However, kaolin is a poor choice for this type of project. The green strength of kaolin (porcelain) hovers around 400 psi, while ball clays approach 800 psi. T

Hi Dexter; Your tandoor is a version of a rocket stove (google). You are dealing with expansion (heating) and contraction (cooling.) In this case: low thermal expansion. The silica sand is typically 30-40 mesh (Home Depot) is to help control expansion by creating voids in the clay body; for the same reason sheeps hair is used. The hair will burn out, leaving voids. Voids will absorb expansion that would normally cause issues in traditional pottery. There is a simplier way to get there: find the lowest expansion commercial clay available; these are normally sold as "ovenware" bodies. Grab a bag of charcoal; yep, the BBQ stuff. Grind up the briquettes into a powder (wear a mask, outside). 30-40% is typical. For easy math- a 25lb bag of charcoal will do 75lbs of wet clay. When fired, the charcoal burns out, creating voids. Same principle, same result- much easier. Tom

Have 4 Paragons, and hit this issue on 3. The wires from the thermocouple to the block are constricted in a narrow channel, typically less than 1/16th separates them. The heat caused enough expansion that caused the wires to touch. Ended up putting a small piece of fiber insulation between them, after I separated them (very carefully). Tom

Granular Magnetite (iron) at 2%. From wet clay calculate 20% as water. 10lbs minus 20% water(2lbs) = 8lbs. Dry x 2% granular Magnetite. Judging from pic- 20 mesh speckles. Make a 500 gram test batch and fire as a tile with usual glaze to judge speckle population. Add or subtract as per personal preference. Iron will be safer in your case given kiln location: granular manganese can fume.

Never had an instructor: then again I never intended to go down the rabbit hole this far either. I noticed early on in another forum where I lurked mostly: there would be ten different answers to one question. I understood that application and style could vary from potter to potter: but never made sense on the chemistry end of the equation. So I made the decision early on to seek out information by those with PhD behind their names. Oddly enough, found variance there as well- who knew? If I had a mentor; that would be Ron Roy: who I had the pleasure to spend three days with at NCECA in KC (2016). We email back and forth to this day. I have been asked several times to do classes in St. Louis- to date I have always declined. My wife, siblings, and two friends even know that I am involved with clay. Has always been my private sanctuary: and never discuss it locally. Tom

Oddly enough: I would like to spend a day unseen in a corner, watching a newbie throw their first form, open their first kiln firing, or sell their first cup. The joy and excitement is contagious. Would have loved to spend a day with W.G. Lawrence (Phd@ Alfred) and pick his brain. Same for Orton Jr, Koppatchu, Horton, and a few others who laid the foundation on which modern pottery is built.

Sbsoso- welcome to the forum. You did not State clay body type: but I will go with porcelain. When doing production: not a bad idea to keep 25lbs from the previous lot to compare to the new lot if problems arise. No problems before, and now problems means the first stop is to check with supplier if others have reported issues. Like potters, clay manufacturers shop for low prices: which sometimes creates issues. You have a plasticity issue which you can only resolve by adding water. Adding water does not increase plasticity; just moves the body closer to its liquid limits. Adding water will also increase drying issues such as warping. Your plasticity issue is caused by one of two things: the % of plasticizer has been lowered, or the plasticizer (ball clay) has lower plasticity properties. The second is Nep Sy being used as a body flux. Nep Sy has 14% soluble salts that can migrate: which can cause rapid dehydration of water. Sodium is hydrophobic- fancy word for- not fond of water. Again adding water compounds the problem by allowing further migration of soluble salts. As others stated: de-airing pugmill has zero influence. All a de-airing pluggers does is remove the air between clay particles which speeds up the transfer of negative particle charges. De-airing has zero influence of the actual chemistry of the material. Tom

About half the tradesmen around here retired, or moved south. Of the other half: 90% are 45+ years old. Everyone once in awhile I see 20-30's at the lumber yard. Local colleges and schools ceased trade classes over a decade ago. Most schools have dropped art classes. Local community college cut pottery classes way back. State college still has a strong pottery criteria; but heavily focuses on sculptural work. Prez: that would be an interesting question: do your local schools/colleges still teach pottery courses (historical, not Covid related) Changes in focus, technique etc. You get the drift ; phrase it as you wish. Curious to see changes.