Jump to content

glazenerd

Members
  • Content Count

    2,999
  • Joined

  • Last visited

Everything posted by glazenerd

  1. CD: thank you and your welcome. Let me qualify my response by saying: I have not personally fired crystalline in a manual kiln. That said: I know many who have and still do. In the many lengthy conversations I have had with manual firers', it requires constant monitoring during the crystal growth ramp holds, Firing schedules which includes ramping down from peak (cone 6) to growth ramps (cone 04ish) requires keeping a careful kiln log of switch settings, length of time, and kiln chamber "color." Firing manually is not impossible, but it is about as tough as manual firings can get. I can certainly reach out to those who still do for helpful insights, although it might take awhile to get a response. One of our forum members fired crystals manually back in 1973 with good success: perhaps she will chime in. Tom
  2. Bill: I sent this testing to Ron Roy and Tony Hansen a couple of months back for peer review. Ron stamped it and Tony is "taking it for a test drive." A forum member sent me a sample of wild clay to test not too long ago. In the first pic the raw sample is on the left, results of the first phase LOI (middle) and Imco Burgundy on the right for comparison (iron levels) it was fairly plastic in the raw state, but extremely short after the first burn out phase: which means plasticity was derived from organic Ord humus ( black streaks in clay) In the second phase (in dish) the iron became apparent as did the calcite ( white granular)
  3. 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, plasticizers, and hectorites. LOI of clay is considered when trying to calculate the properties of raw clay or blended bodies. LOI for individual raw clay is an important value for judging the suitability for use in a blended body. This value is a direct indication of contaminants such as lignite coal, sulfides, and sulfates: all inorganic carbons that can cause issues in a firing. High sulfur content in a clay body is directly expressed by higher LOI values. Dark and red bodied clays contain higher levels, but high plasticity ball clays usually contain higher carbon content. The general rule of thumb: highly plastic ball clay fields are typically located adjacent to coal seams. Historically, calculating LOI totals was based on a single firing of raw clay or other ceramic materials to 1800F/1000C. Often times material analysis were performed, and a LOI value was inserted to balance the totals to 100. Kaolin can have high LOI values due to the chemically combined moisture content; referred to as molecular moisture. The molecular moisture content of kaolin can run as high as 14% of weight, but kaolin is otherwise fairly free of inorganic contaminants. Ball clay on the other hand has little to no molecular moisture content, but can have inorganic contaminants higher than kaolin. Calcining kaolin in order to reduce shrinkage in slip and glaze recipes is a common practice among potters. Many potters calcine kaolin to a bisq temperature which is not necessary: molecular moisture is driven off by 1112F/600C. This temperature is just prior to when combustion begins to occur in the kiln chamber. Inorganic carbons burn off from 1250 to 1750F (665-950C) which include various forms of sulfur: lignite coal and iron (disulfide) being the common contaminants. The temperature range for molecular moisture and inorganic contaminants is the basis for the Split LOI test. For this same reason, this test requires two separate firings to determine rather molecular moisture or inorganic carbons are being burnt off. Test Protocols: field clay must be cleaned by the slurry method and debris removed. Then throughly dried and ran through an 80 mesh sieve. A finer mesh is required to remove remaining sand or large particles. 500 grams is required in order to detect small variables in either the first or second firing. Most scales used by potters are not sensitive enough to detect small variations in lesser sample weights. Samples for the second firing should be placed in a shallow form to protect shelves in case some fluidity develops. Do not add any other materials to your raw clay sample. Fire in oxidation, spreading material evenly in a shallow form on slow ramp speed. The first firing is to measure molecular moisture and/ or organic carbon content. If properly cleaned, organic carbon content should be minimal. Fire to 1112F/600C with a short 10 minute hold to ensure uniform heat distribution. Upon cooling, weigh the test sample and note LOI loss. Fire this same sample the second time to 1800F/1000C with a short ten minute hold. You can fire the second sample as part of a normal bisq firing if you choose. Upon cooling, weigh the sample and note the LOI loss separately of the first firing. The weight loss noted in the second firing is a direct indication of the inorganic content of the sample.The combination of the first and second firing is the total LOI for the material. If you recorded high LOI loss in the first firing: your sample is kaolin or kaolinitic in composition. The exception would be ball clay with high organic content which usually presents as black or black streaks. Kaolin has much higher molecular moisture content than ball or fire clay. If your second firing recorded higher LOI than the first firing: then your sample is either ball clay or fire clay. Ball and fire clay have little to no molecular moisture content, but have low to higher inorganic carbon content. To some extent the LOI loss in the second firing can indicate the plasticity level. Highly plastic ball clay is typically located adjacent to coal seams with higher inorganic carbon content. Not conclusive, but higher second firing LOI values would warrant additional plasticity tests such as WOPL. ( water of plasticity) Additional information can be gleamed from the second firing as well. At 1800F/1000C, enough heat is present to produce color if appreciable amounts of iron are present in your sample. If nodules or fluidity occurs at bisq temperature: both would indicate a low fire earthenware variety clay. Nodules are more indicative of natural fluxes, fluidity is more conducive with low alumina content. Fluidity would then require the addition of high alumina kaolin be added to increase refractoriness. Finally if the sample appears very dark or black, and/or hard nodules have formed: this would indicate high levels of iron disulfide with additional sulfides from lignite coal. This kind of sample would produce blistering, bloating, or carbon coring if not fired correctly. Tom
  4. 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 might be in play? Silicon carbide provides chemical reduction in an oxidized kiln- doubt seriously it is used here because it would alter the color. T
  5. I was suggesting that 1500F was enough heat to cause a chemical reaction: which presented itself later when water was added.
  6. 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
  7. 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 with your first firing- very impressed. You can discuss exact recipe in PM if you have more questions. Tom
  8. 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
  9. 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
  10. 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: then it should handle cone 6 because hematite and magnetite clay runs between 20-24% alumina- iron disulfide runs 15-17%. The test is simple: just put a button of you clay on a tile, scrap whatever and cook it to cone 6. Brown- iron disulfide- low fire. Deep red- hematite. Plasticity- your sample has high sand content which is "tempering" the clay- not the same as plasticity. Tempering comes from the brick industry- used to produce malleability, but not plasticity. (They do not want high shrink values). Plasticity- start with 20% OM4. EX. 200 grams OM4 per 1000 grams local clay. You are hand mixing I assume? If so, it will take 3-5 days before full plasticity will develop. Overdo the plasticizer then you will have the opposite problem of clay fatigue- slumping-folding. Burn a sample to cone 6- confirm what the iron source is: then address formula- cone value. Nerd
  11. Cone 6 stoneware 76% OM4, 14% feldspar, 10% silica. ( This is a plasticity fix only.)
  12. 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
  13. 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.
  14. 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.
  15. 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 application looks like. To further explain technical terms: when you open the kiln expecting beautiful crystals and see this: the immediate reaction is "crap." Descriptive on both a chemistry and emotional level.
  16. 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.
  17. 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.
  18. 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 "stretched membrane" theory in 1948: the basis of modern slip chemistry. Norton describes the measured effects of sodium silicate in solution: resulting in a particle range from 0.14 to 0.57 microns..or in pottery terms 30,000 mesh. If you are a big terra sig person: first buy Taylor ball clay from a Old Hickory Clay Co. In Kentucky. OM4 has a median particle size of 0.67, and Taylor 0.31. Which means you will get over twice the payload for your efforts. With freight, Taylor will cost you 0.50 cents a lb- but they sell 50lb bags only. Second is an ionic charge trick I will teach you. Lawrence and a Buttons also wrote on the effects of temperature on ionic charge. At 60F, the ionic charge that suspends those fine particles potters want in terra sig drops by 1/3, which directly effects the amount produced. However, at 140F, the ionic charge is at its peak: which means the quality of fine particles held in suspension is much higher- resulting in more yield. The trick: heat the water to 135-140F ( but no higher), add your sodium silicate first- then your Taylor ( or OM4). In 1-2 hours when it cools back to room temp 75 or so. Siphon off the goodies as usual. You now have more sig in two hours than in 24 hours. So remember folks- you heard it here first. As other potters hack the info from this site and add it to theirs and claim a great discovery- you heard it hear first. Enjoy Gordon tom. - was going to make a CM article out of this... But hey. Several recent threads on image theft, cultural theft: but theft of intellectual property is never mentioned.
  19. 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 PM before- W.G. Lawrence " Ceramic Science for the Potter." F.H. Norton " Fine Ceramics, Technology and Application". And the book referenced above are the best encapsulated information resources. For the record: I have journal references lying all over the place in my various threads. Feel free to go find them. Long past tired of having post proof every time I make technical posts. Tom
  20. 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 friend. Tom
  21. 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 difference in a large chamber. Years ago I started mixing my crystalline glazes via PH meter. I raise the PH in cold spots, and lower it in cold spots: works fairly well. I would put conduction up to 2000F, and radiation there after. Edit add: If Edison did not have Telsa: his inventions would have been few. IMOIMO Tom
  22. 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 out of Germany was studying local materials, and reported the reaction at 2050F. So 2050F spinel to mullite temp has been confirmed numerous times. U of I (Champaign/Urbana) has numerous studies up on their Ceramic Technology site. I posted a link in one of my ramblings somewhere : stoneware study thread I think. They used X-ray diffraction to analyze heat work and the phase changes in potassium and sodium. At 2190F, sodium and potassium are spent- no longer visible. I cannot confirm this: but I suspect this is where the commonly used 2190F peak with hold firing cycle came from. Orton Sr. Did extensive studies back in 1909-1919 range(?) noted in my Nerds Firing Schedule thread. He proposed the 108F ramp speed for several reasons: primarily to burn off inorganic carbons, secondly for heat work purposes. As you well know, cones are based on Segers work, but Orton did the initial testing on calibrated heat work. did I answer them that time, or do I need a third cup? Check my Stoneware study thread, Nerds Firing Schedule thread, and possibly my Porcelain thread. I have links to studies floating all around. I do know some studies are no longer accessible: Wiley Library has been buying them up and archiving them. Tom
×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.