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Posts posted by glazenerd

  1. Mark:

    I retired from home building last spring. I tried retirement back in 1017: taking most of Dec. until late March off- until boredom sat in.I work because I want to, not because I have to.  I had the same thoughts when I read the post- a trend. I also realized that sitting at a wheel making cups and bowl is not working for me either. If I had any creative ability; I would do sculptural pieces; but I do good to paint by number. So, I will go back to making geometric tile: requires less thought. 

  2. PD

    I have some historical knowledge, after retiring from 45 years of home building. There were several plants in the Us at one time, but most are gone because synethic materials have taken over the market. I believe the one in zflorida, and California are still operational there were brickyards in almost every state from the 1870,s until after WW2 because weight made it too hard to ship.many of those brickyards also made Terra Cotta roofing tiles. 

    Most all tiles made in North America were the classic Terra Cotta orange because iron disulfide is the most common iron source here. Some deeper orange and reddish colors came out of NY, Arkansas, Oklahoma, and Georgia because those areas have megnetite and hematite iron deposits. 

    One notable difference in historic tiles was the nail punch pattern, In North America, a round single center punch was used. Ital, France, and Spain used a square punch, until the more recent decades. European tiles were generally thinner because they could fire higher because of the iron, American/ Mexican tile was thicker and fired lower.  

    It is most likely locally made; and a good chance the brick yard that made it is long gone. Check with your local historical society. Pending the age; it could have been imported from Mexico as "Spanish" tile. The odds that it was imported are minimal. If it is a point of historic s importance: you could have a crushed sample analysis done and identify the iron source. 




  3. Hannah:

    premixed slip uses Darvan 7 or equal as a long chain deflocculant. This type of ionic polymer works by neutralizing sodium and magnesium ions. When you added Epson salts: you added magnesium strearate which disrupted that chemical suspension which caused flocs (clumps) to form. Adding sodium silicate, epson salts (magnesium) causes a chemical reaction. In the future, to thicken it- it is best to add dry powdered clay you recycled from throwing, dried slip or whatever source you can recycle from. 


  4. UNESCO (United Nations) catalogues and records significant cultural art and artifacts- including pottery. The link below is for a remote village in Ukraine that does hand painted pottery. (Stunning) Follow the UNESCO links for a complete list of unique pottery from around the world.



  5. Gen- I will add SoCal to my list. From the color response you are dealing with iron disulfide. I would fire to cone 3, and check color response: then fire to cone 1- and check it again. I will assume you are after classic Terra Cotta. Once you determine the highest cone value verses color; you can then build flux additions around that cone to lower absorption. 


  6. Gen:

    In the USA; iron bearing clay sources iron disulfide (most common, hematite, or magnetite. Iron disulfide is easy to spot because it fires into the brown range at cone 6; along with the typical bloating, blistering and black coring commonly associated with it. Hematite and magnetite will keep its classic "Terra Cotta" color, deepening into reds, reddish brown as you fire over cone 6.  The green native clay you show is common down in the Carolinas; the green cast coming from chlorite materials. The other issue you will find in conjunction with iron; is the alumina content. Alumina is obviously refractory and plays a key role in maturation temps. Low alumina (15-16%)will become molten at cone 04. As the alumina increases (20-24%) it tolerates more heat (cone 5-6) and 26-30% cone 10. Alumina levels also play a role in color development as well. Native clays with higher alumina content and iron bearing will keep its color to higher temps as well. Fired buff color 2-3% iron, Terra Cotta 4-5% iron, and you can reds, purples- 6-8% iron (magnetite or hematite only) with higher titanium levels.

    Tom. Do a search on Facebook for "Clay Tech".. lots of clay info there.

  7. Sarah:

    I looked up your Super White: which is Grolleg kaolin based, but also uses ball clay as a plasticizer. Grolleg is about as clean as clay gets and fires high white; however using ball clay introduces contaminants such as magnesium, titanium, and iron. In this case it is not iron, but rather magnesium reacting with titanium. In addition, this body has higher flux levels which also play a role in creating the brown toasty color. Leave the plug out until 1100C, and do not allow pieces to touch each other, nor should you stack them. See test bar 4 below: which is high titanium, flux, with lower iron and magnesium.


  8. I have seen that purple before in crystalline glaze. Titanium reacts with iron\ zinc when fired in reduction to produce purple. I have gotten purple in oxidation using prescribed levels of iron and titanium. I would start an experimental recipe with 8% titanium, 3% iron, and 4-5% zinc: and reduce on the cooling cycle. I do not know the exact recipe, although by the run Nep SY is most likely the primary flux.


  9. Lots of info and insight-TY all. Typically I take 3-4 pictures a month, but that will increase dramatically shortly. I have over 500 test tiles that I need to shoot and catalogue, with corresponding data. My camera skill extends to point and click. So, I am looking at several models that have single button "macros" setting, with some zoom and higher resolution. Did I mention I have a great dislike for shopping for anything. @JohnnyK I would make a lousy PI; all my photographic evidence would be blurred.

  10. The pic I posted was actually a Terra Sig experiment, that was taken outside in full sun. You can see one sludge line, but there is a continuous shift in color below it which I need to capture.  Bill, I know lighting plays into it, but I really do not want to get overly involved in photography set up- I do not sell pottery online. Liam- your corrections are getting closer. LT- I just saw "raw" last night when doing some research, that caught my eye. Bottom line- need to educate myself a bit more before making a purchase. What I know about cameras would not fill a post-it note currently. 

  11. Well, learned something today- macros. Nice close ups. Perhaps I should restate: I need a camera for much sharper images with slightly closer images. I have microscopes with USB for extreme close ups. Although Sony does have one with some macros capability, perhaps that would be a better choice. TY gentlemen.



  12. gallery_73441_1093_741956.jpgAs you get closer to the target growth ramp temp: crystals will close up and fill in to form round florets. Crystal formation 1 is about 20F degrees off from the "perfect" crystal formation. If you held at 1970F, you would lower to 1950F. Crystal formation 2 is about 10-15F off from the right growth temp. Watch your formations: they will tell you how to adjust the heat. 

    This are "floret" crystals.


  13. Hi Jess:

    I see you like nickel carb: rather fond of it myself. 2 things to work on-1. Over population of crystals. 2. Firing schedule; more specifically growth ramp holds. 

    Zinc is used to control crystal population. In this case you need to start with an 0.50% reduction in your current recipe. EX. 25% zinc in recipe reduces to 24.5% zinc. Simply increase the silica by 0.50% to offset the zinc reduction.

    Ramp hold: in between the 2 large blotches of blue is a Maltese crystal formation: some refer to it as an axe-head crystal. That formation is the biggest indication of how you need to adjust your ramp holds. In this case you need to lower your first ramp hold by 10F. EX- 1950F is lowered to 1940F.  Remember: if the recipe you are following says 2 hours @ 1975F- that could be 1950 to 1990F in your kiln. Kiln chamber size, thermocouple type, packing density, and thermal mass ( heat loss/gain) will always vary from kiln to kiln.

    The large blue blotches are primarily over saturation of glaze. ( re-applied & refined) The outer crystalline ring is a low temperature growth pattern which results in a course/open threading. I can see minor grainy/course threading which is called "felting" in the crystalline world. Felting is a big indicator of excessive glaze application or excessive colorants ( cobalt is notorious for felting)

    I do not want to over load you with info- address these 2 issues and go for round three. 


  14. Cole:

    Fred is correct: temperature of the slip effects ionic charge: which in turn effects particle stacking. F.H. Norton PhD @ MIT Wrote the original theorems on slip chemistry back in 1948. IF your slip is formulated correctly, deflocculated correctly, and the temperature is correct: then setting should occur within 15 minutes. Temperature of the mold could double that time. The other variable is soluble salts: which in modern times would be Nep SY used as the body flux.There were numerous studies done on the effects of soluble salts on casting rates, viscosity, particle suspension, and segregation. Those studies showed that soluble salts should be kept under 0.30%, which brings us back to Nep SY with up to 14% soluble salt content. 

    If you can keep the temperature of the slip and molds at 75F, it would alleviate your warping issue. You would have to do absorption testing to verify the effects of soluble salts. EX: if your premix slip states 2% absorption at cone 6, and testing shows 3-4% at cone 6- then you are still dealing with particle segregation caused by either temperature, soluble salts: or both.


  15. D.D. Button & W.G. Lawrence PHD-Alfred U, "The Effects of Temperature on the Charge on Kaolinte Particles in Water"

    @68F the ionic charge responsible for suspension begins to drop: which in turn changes how particles "stack" as they drop out of suspension. The ideal "stacking" arrangement of particles is called "card stacking": which means particles are arranged tightly and uniformly. If the particle charge supplied by Darvan or by SS and soda ash is too low, or temperature is too low then they stack by particle size (A!B!C!) or "flat stacking" which results in warping. The ideal temperature is 90-100F, at which point temperature actually aids in suspension. The maximum temperature is 140F.

    Applying this principle visually: maple syrup is firm in the freezer, thick in the refrigerator, heavy at room temperature: and thin when heated. The temperature directly impedes or accelerates particle suspension by allowing/hindering particle motion (collidial chemistry.)


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