glazenerd

Grackle: the technical aspects of your question: clay continues to expand up to 2050F; at that point, the porous body begins to contract until it hits maximum density. (Vitreous state). At cone 04; (1975F) the pores are smaller; therefore the absorption is less. As Hulk pointed out: cone 04 bisque absorbs less glaze. I have used cone 04 for decades because I can control glaze application better. Inorganics in clay; primarily in red, and darker brown bodies burn out between 1250-1750F. The reason a slow bisque fire is required for these types of clay: it takes up to 30 additional minutes of the ambient kiln temperature to penetrate an 1/2” clay wall.. The slow bisque cycle allows that to occur. As with all things clay: dive in and take cone 04 for a test drive and see if it works for you. Tom

TY- I misread it.

Njabeid: The reason we are looking at so many variables; I do not think any of us have seen 2% copper addition cause such a reaction. Tom

Very few have the privilege of seeing there life history. Congrats.

The clay is locally sourced (wild) clay 1. Without additives. Wild clay typically comes in at a lower COE of commercial clay. 2. Zoom in on the flaked areas, and you will see white flakes. Those flakes are most likely calcium based; IE lime pop. Those specks could also be silica based minerals- unmelted silica has a COE well above 10. At the moment; calcium tops my “probable” list. Tom

Sorry Babs; Just now coming back online; my 15yr old IPad finally said goodnight- was waiting on Santa Claus to show up. Actually, I was waiting for after Santa Claus sales to buy one. This has been an ongoing discussion for many years now. There has been numerous references to brick, tile, and other products used outdoors. Brick for example relies heavily upon “black coring” to occur that produces nearly a zero absorption value. Modern talc body tiles rely on the high magnesium content to produce very low absorption rates. Porcelain has to produce enough glass/mullite content to reach a vitreous state. Grog used in brick making is for malleability; in lieu of plasticizers; but black coring still produces the density and nearly zero absorption rate. So in translation: a red bodied clay must be fired hot enough to create low absorption, or intentionally fired on high speed to produce black coring. Talc body (low fire 04) must have enough magnesium content to produce low porosity. Porcelain at cone 6 must have a minimum of 30% feldspar content to achieve low porosity. Like anything- have to test final results. T

Years back I did a 1/3 kaolin. 1/3 frit 3110, and the balance in silica and ball clay. Fired to cone 04 as I recall; very low absorption. It is very doable, and 1.5% absorption is well within reason. Enjoy the journey. Tom

They know where "no hunting" is allowed.

As a friendly reminder from my front yard--

Rebs: Pinholes come from off-gassing feldspars: blisters come from off-gassing inorganics- primarily from iron disulfide. (sulfides) You either slow the firing down between 1250-to-1800F, or slow the kiln down from 2050F up to peak (cone5/6). The brown splotches of color in the tan area of your glaze is a goodindicator of iron bearing clay: in this case iron disulfide. When a crater forms around the blister, and barren clay can be seen in the center of the crater: almost always inorganic materials burning off. -- Tom

Yes. I took 4 years of wood working, and 4 years of architectural drafting. Small engine repair, lathe, metallurgy, welding, and 2 years of mechanical drafting. 2 years of electrical wiring, a semester of electrical motor repair. I took Home Ec my senior year, but I already knew how to cook. Some farm classes, which were pretty much useless because I was a farm boy anyway. I excelled in chemistry, always had a curiosity about it. Enrolled in a local college to major in chemistry until I realized I would spend the rest of my life in a cubicle- so I dropped out. Tom

The term is pyroplasticy: caused by low alumina. (16% alumina would be my guess). Pyroplasticity can be compounded by naturally occurring fluxes. If you want to use it as a clay body; then you need to add 20% kaolin (any kind) to raise the alumina level. Kaolin has 37% alumina typically. It could be used as a slip, but like glaze: low alumina levels makes it unstable. It could be used as a glaze with low levels of flux additions at cone 5. However, low levels of alumina will make it unstable. Using it as terra cotta at cone 04 (as mentioned above) is the best option. You have iron disulfide bearing clay; which goes brown once you get above cone 3 or so. Tom

Ryan: Particle size is not the only indicator of plasticity: although it plays a predominant role. The scientific community measures in um; but most pottery literature is given in mesh. micron, or sub-micron particle definitions. Older pottery and geology books cite "clay mineral"; which has been replaced with "montmorillites." Bentonite and hectorite both are classed as "clay minerals: which by definition means a mineral with clay properties. In addition: plastic characteristics are also determined by aluminum levels, and naturally occurring calcium, potassium, and sodium levels. Particle structure also plays a role: a 1/1 particle (kaolin) is very low plasticity; while 2:1 particles (ball clay, bentonite, hectorite) can be very high in plasticity. If you want to do a deep dive; I will send you some links. Tom

Wood Ash is out my wheel house: but I do recall reading some on its chemistry. It will be high in sodium, potassium, and or calcium; pending which is most abundant in the soil where it grew. I also recall most ash has phosphates as well. I also recall reading an article on Meissen poreclain (Germany 1790's), and they used calcium phosphate as a plasticizer, and to create a paste. Tom

Interesting topic. Trying to find some old documents that detailed deflocculants used in the 18th and early 19th centuries. I would point you to libraries and galleries at Kent on Stoke in the UK. I do recall reading several documents detailing this issue: but again too long so my memory is fuzzy. I also recall Taxtile Doat (Serves in France and The University Pottery in St. Louis) detailing this topic as well. I could go on a deep dive about the chemistry, but that will not help you with a definitive answer. I do recall calcium phosphate being used as a plasticizer. Tom

Tina Bentonite can absorb up to 15 times its weight in water. So adding 70 ml does not come as a surprise. from what I see, looks like your in the 75ml range total. The main thing is to keep records as you go. Be sure to mix clay and bentonite well before adding water. Additional note: powdered clay has silica: mix outside if you can- wear a mask until you get it moist. Tom

Tina: I made some assumptions based on the information you have provided so far. I also converted to metric- 1/4 Liter of clay = 220 grams +/- add 5grams of bentonite ( or 5ml ) My bentonite came out almost exactly 1 gram = 1 ml. Add 1 teaspoon of baking soda to 1/4 liter of water and shake well (stir). Then pour off 60 ml of water only; to be used in the clay. Do not allow any residue from the baking soda into the clay. The actual amount of water needed to form a clay ball should be around 50 grams. Once you blend into a pliable ball: let it stand 3-5 days before checking plasticity. Plasticity is not automatic: it builds up to a peak over a period of days. This is a base recipe/starting point: may need adjusted as you check plasticity levels. Once you reach a workable formula: simply multiply the base to make larger batches. *** had to hijack my wife's computer; my 16 yr old Ipad is on its last leg. Tom

Final before I go to work (suppose be retired- yeah right! Once I figure out a measuring system for you; I am also going to do a PH test. I use a PH meter to mix certain glazes, and to check alkalinity levels of certain clay blends. The short term fix will to be add a specified amount of baking soda to your water; stir and dissolve it: then pour off the water- leaving the residue behind. That alkaline water will then become what you mix your clay with. I will PH check it to make sure it is not too high. There only needs to be a minimum amount of PH to break the effects of acidity; do not need much. Tom

Tina: I used baking soda for an experiment because you did not have access to feldspars. Clay reacts to two extremes: acidity creates strong flocculation; but equally strong alkalinity (above 9.8 PH) also creates very strong flocculation. The PH of baking soda would be classified as "caustic" in the clay chemistry world. For that reason, I asked you to google search potassium fertilizer; trying to figure out an alternate source that is readily available to you. Tom

Tina: One final experiment: take a golf/ ping pong ball size piece of your brown clay. Add just a few drops of water and wedge it it; needs a little more moisture. Then put a "pinch" of baking soda on it; wedge that in. Then add a second pinch of baking soda; then wedge that in. Let it sit about an hour. and do the coil test- wrap it around you finger. That will tell me how much acidity/ and or positive charges (iron and alumina) is effecting plasticity. Once I know that; this weekend I will measure out and weigh a clay I believe similar to yours. Then weigh out how much bentonite. I will post a ratio: x amount of bentonite for every cup of clay. You can then mix by multiplying that base recipe. Unless you have a scale; then life gets easier. Tom

The term is "amphoretic." Certain acids (vinegar/lemon juice) when mixed with other acids create a specific reaction that creates alkalinity. One of those "freaks" of chemistry. The Amish use a mix of vinegar and herbs to treat acid indigestion for that reason. The other thing missing in this equation is: commercial clay bodies have 10-35% feldspar content: your body has 0-1%- so the intended reaction will not occur. I will resist my urge to go on a long rant about monovalent sodium ions. Tom

Tina: a heads up; I do not have a smart phone, and my Ipad is about dead. This means I can only respond at certain times. Tom

When you wet process wild clay: 1. Put your clay in a bucket large enough to cover it completely with water. Agitate it, then let it sit for 1-4 hours; until you see a clear water film on top. Pour off the excess water, then slowly pour into another bucket until you reach the layer that has debris. Throw the debris out. Then pour your clay through a pillowcase, and hang it up somewhere until the excess water drips out. Allow it to dry down to a workable clay consistency. Tom

Sent an email to a Russian potter, another in the Chech Republic: both collect and process wild clay. Trying to get a handle on what is available in your region. Tom