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Everything posted by glazenerd

  1. I developed this test primarily to test clays: you will not find it in text books- it is being introduced for the first time. Split LOI Test Loss on ignition is a chemistry term, measuring the amount of organic/inorganic material released from solids, when they are heated to a temperature that is high enough to produce combustion. In pottery/ceramics, the definition is widened and application broader. LOI is applied to minerals such as silica, feldspars, talc, dolomite, and other commonly used glaze ingredients. In addition, LOI is also applied to clays, bentonites, plasticize
  2. Bill: Small amounts of manganese in crystalline glaze produces silver crystals. That color only results when an ionic bond occurs which creates a distinct crystal lattice- hexagonal closed pack ( most glazes are covalent bonds) That ionic bond is heat sensitive- which darkens the color to a bronze luster. I suspect (not sure) this glaze may be using one of two industrial pigments or metallic Frits. One company makes metallic coated Frits, the other makes high temperature pigments. MEA is an emulsifier- chemical suspension agent. The use of MEA also suggests to me that metallic Frits mi
  3. I was suggesting that 1500F was enough heat to cause a chemical reaction: which presented itself later when water was added.
  4. Lee- I get questions about crystalline on a regular basis in PM and email; and will answer publicly when asked or if from someone I have been working with. I still read what is posted on a regular basis. Been working on a couple of articles for CM about the finer points of firing crystalline glaze: as Brandon just proved in his first firing- not as tough as it looks if you know the "tricks." Tom
  5. Brandon: excellent results for first firing- I know many have not gotten this far in 30 firings. You are to be commended for researching and learning before diving off into the deep end of the glaze pool. I like to use crystalline posts as an educational opportunity for those who are following- there are many. You have the peak temp, growth ramps, and recipe down. A reactive recipe will grow crystals at the rate of 3/4 to 1" per hour of soak time. Great crystals on this one- exceptional in fact. Again note the cloudy (milk) on the upper third from excess titanium. I am very impressed
  6. Marcia: Speaking of crystalline glaze- I read a thesis paper on crystalline glaze written by a student at SIU-C in 1973. As a historical perspective: 1973 was 25 years before any formal books on crystalline glaze was published ( Macro Crystalline Glaze by Peter Isley) I have read it several times: the insights and theorem are well within the boundaries of modern crystalline chemistry. The author of this thesis paper was YOU. T
  7. Frits begin melting in the 1475F range. "Dictionary of Glass and Technique" by Charles Bray. Best resource book on glass, including making frit. Look at the course ground here- https://shop.bullseyeglass.com/accessory-glass/frit-powder.html
  8. Gen: Gold specks possible pyrite: but not mica- mica would be glassy or white. Pyrite is FeS (sulfur) and judging by your result with 50 local 50 B-mix: you have in excess of 8% iron content. The only issue that makes me doubt pyrite is the dried greenish color: hematite in the presence of calcium will present greenish. The simple test to determine that: iron disulfide (pyrite) will go brown at cone 6- hematite will keep a deep red tint. Alluvial soil is fine grained- sub micron and lower in alumina. If pyrite, doubt you can fire past cone 1-2 without pyroplastic issues. If hematite: th
  9. Cone 6 stoneware 76% OM4, 14% feldspar, 10% silica. ( This is a plasticity fix only.)
  10. Coleman Porcelain. >Aatdvark Clay is highly rated for Cone 10. Laguna Frost porcelain- cone 6. Any "high white" porcelain will work. Translucency is not a requirement for crystals. Colorants should be 325 mesh. Alumina, titanium dioxide, red iron, copper carb, manganese, cobalt carb. ilumenite, and rutile are commonly used in crystal recipes. Small quantities: very little colorant goes a long way. Nerd
  11. Liam: acid etching usually involves full strength muratic acid with only mild dilution. Typically the PH hovers around 1.5- very corrosive to skin, eyes, and inhalation of fumes can damage lung tissue. Not only requires eye and skin protection, but also respirator for those specific fumes. If left to soak indoors: can rust any metals within a few feet within hours. Seriously bad idea to make that suggestion to a screen name with "hobby" in it. Yes, I play with some potent stuff: but I have the safety equipment, and the training (EPA) to do so. And I dispose of it within recommended guidelines.
  12. By the way- stay far away from acid baths: dangerous if you do not know what you are doing and do not have the proper safety equipment.
  13. In the crystalline world this is called: "Crap." If you do not get results in the initial firing: odds of recovery in a second fire is slim to none. However it is a good lesson of how colorants and oxides disperse in a firing. Notice the large run lines of the cobalt and the white streaks (tin) going down the sidewalls. This is also a good lesson on glaze application. Vertical pieces- 0.65-0.75 grams per square inch. Flat surfaces- 0.45-0.50 grams per square inch. When glaze application is excessive: it will pool and crystallize. A good record none the less: you now know what excessive glaze a
  14. Notice the streaks running down the side walls? In this case: that is the tin and zinc pooling to the bottom. Lose too much colorant- blotchy crystals. Lose too much zinc- no crystals. In dead center bottom there are too large blotches with raised rims. That is called "boiling" in the crystalline world. It is caused by excessive peak temp; but also common when excessive lithium carb is used in the recipe. Cobalt is reactive to excessive heat and/or excessive flux: boiling is a direct indication of those problems.
  15. Jess: going to turn your results into an educational dissection of results. You have inner and outer growth rings: just need a mild downward adjustment in ramp hold (growth) cycle temps. Do not worry about the crazing at this point. Dial in your peak melt temp, then your growth cycle temps : then adjust silica to control crazing later.RULE 1: only change one parameter at a time when testing crystalline: so you know exactly which change caused what reaction. Final assessment: you did exceptionally well for your first time out with this glaze- be proud.
  16. Actually Mark, your email convinced me to make one more post. The reason I am disconnecting is at the bottom. I cut and pasted this from the Crystalline Glaze forum- to where I just posted it under my user name there. ------------- Actually Gordon, I have been reading about the effects of PH on ionic exchange; in part the theory behind a terra Sig. Norton (M.I.T.) and Lawrence & Buttons (Alfred) did the original studies on slip starting in 1948-1974. Norton actually started the whole sodium silicate/terra sig when he was studying the effects of PH on the water hull. He wrote the
  17. LT: there are 100 plus references to journals, thesis, books, and other resources on the effects of temp on clay bodies. https://books.google.com/books?id=pQpCDCPqlS4C&pg=PA58&lpg=PA58&dq=W.H.+Sutton;+factors+influencing+the+strength+of+clay+bodies&source=bl&ots=AfkxuypAxo&sig=ACfU3U2W_Zh8NTluxpwvcnIN4zVOWBV3vw&hl=en&sa=X&ved=2ahUKEwjB-_rwj7jiAhUPnq0KHaUpC_YQ6AEwAXoECAQQAQ#v=onepage&q=W.H. Sutton%3B factors influencing the strength of clay bodies&f=false you need to hire a research assistant: I am a little busy. as I have told you in
  18. Bill: results from Ougland & Brindley study on heat work. 2192F (1200C) minimum further development of the clay body after this point. Minor decreases in absorption, along with minor increases in glass content. See chart below. Typical cone six ramp hold temperature for maturity. ----------------- --------------------- 2192F (1200C.). Glass 62. Silica 21. Mullite 19 2372F (1300C). Glass 66. Silica 16. Mullite 21 (Ougland & Brindley) Off topic, Ron Roy emailed me: he is doing a work shop nearby in June. Looking forward to seeing my
  19. If anyone ran measured effects of heat work, it would be Orton Sr. He wrote several abstracts for American Ceramic Society, I will nose around and see what I can find. The other source would be Ougland and Brindley from the British Ceramic Society: "Effects of a High Temperature on Kaolinite" I read that abstract, and quoted some of it in my threads. It has since been pulled down, sadly. I have been pricing gradient kilns: and potters gasp at the price of an electric. Keep waiting for a good used one to come along. From my observation pending kiln size: there can be up to 40F differen
  20. Sorry Bill, I broke my two cup rule. Never answer questions until I finish the second cup. As I recall: one study was done in Brazil , one in India for their Government, and one in Germany? All three used gradient kilns with 6-10 chambers and 10-15C variation between chambers. The one in India was testing laterite, and reported an exothermic reaction at 2050F. The study in San Paulo? Actually used bars in various thickness 1/4 to 1/2 in a multi chamber gradient kiln: that studied produced the time of heat absorption and release at 2050F: conduction being the focus as I recall. The one ou
  21. Bill: Clay goes through three endothermic (absorbs heat) phases, and one exothermic (releases heat) phase. 200-250F atmospheric moisture is driven off. Potters already know what happens when they blow through this ramp too fast. The reason most controller programs have a hold at this temperature. 573C/ 1064F quartz inversion. Pottery books explain this as alpha quartz converting to beta quartz. The technical aspect: at this temperature kaolin becomes metakaolin. Metakaolin is a fancy word for: all molecular water has been driven off. What is missing from the explanation is:
  22. Educational Post Firing Schedule Variables There are several key issues that effect the final firing schedule selected. 1. Functional or Non-functional use. 2. Wall thickness: thrown or hand built up to 3/8". Structural starting at 1/2" up. Sculptural with varying thickness/ parts. 3. High iron/ carbon bodies vs. white body. 4. Single fire vs. bisq. For the bulk of most firings; functional or non-functional and single fire vs. bisq fire comprise most firings. The additional variable is how thick are these pieces? Several universities across the world have done studies
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