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About glazenerd

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    Now & Then

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  • Location
    St. Louis, Mo.
  • Interests
    Crystalline glaze chemistry. Porcelain, Stoneware, Fritware, 04 Colored Porcelain clay research & formulation.
    Ceramics Monthly Articles: Jan. 2018 Cation Exchange (plasticity), April 2018 SSA Clay Formulation, May 2018 Bloating and Coring.
    Feb. 2019 Ceramics Monthly- Clay Body Shopping Guide
    March 2019 Ceramics Monthly - Porcelain 201
    June 2019 Ceramics Monthly Clay Restoration
    Sept. 2019 Clay Memory
    Oct. 2019 Firing Programs

    Email: optix52@aol.com

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  1. 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. Tom.
  2. 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. T
  3. 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. https://usa.mfa.gov.ua/en/news/open/id/76732 Tom
  4. Brandon: The 50% frit content makes this glaze prone to hard panning- the 25% zinc does not help either. I will send you some glaze jelly- will fix you right up. T
  5. Brandon: While there is a reduction in sheen: does not qualify for crystalline matte. Certain oxidizer and opacifiers will reduce the typical high gloss associated with crystalline glaze. T
  6. 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. T
  7. 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.
  8. 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. Tom
  9. 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. Tom
  10. 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.
  11. 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.
  12. Cactus: nice thought but my 15yr old flip phone does not have that capacity. These days, it is off more than it is on.
  13. 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. Tom
  14. Johnny: when I am conducting experiments and tests; I can actually see results in the picture. My 15 yr. old Kodak is long past its expiration date. There is clearly a seperation layer below- but it is blurred at best. Wildlife photos? indeed!
  15. Do any forum members have experience with this camera. I need high resolution, but I also need "zoom" for extreme close-ups. I seem to be rather technologically challenged (by choice), so input is appreciated. Kodak PIXPRO AZ422 Tom
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