Jump to content

glazenerd

Members
  • Content Count

    2,995
  • Joined

  • Last visited


Reputation Activity

  1. Like
    glazenerd got a reaction from liambesaw in A chemistry question for the glazing community   
    I was suggesting that 1500F was enough heat to cause a chemical reaction: which presented itself later when water was added. 
  2. Like
    glazenerd got a reaction from LeeU in My First Crystalline Attempts   
    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
     
  3. Like
    glazenerd got a reaction from Rae Reich in My First Crystalline Attempts   
    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
     
  4. Like
    glazenerd got a reaction from Rae Reich in My First Crystalline Attempts   
    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
     
  5. Like
    glazenerd got a reaction from Babs in My First Crystalline Attempts   
    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
     
  6. Like
    glazenerd reacted to Brandon Franks in My First Crystalline Attempts   
    Hey, Guys,
     
    Thanks for all the help you have given me. (Especially, @glazenerd) Here is the first round of my crystalline pieces. The blue on blue and green on green glazes are from a book, and the blue on green is a glaze I created myself!
     
    Enjoy, and thanks again!



  7. Like
    glazenerd reacted to Marcia Selsor in Important Ceramic Artists Who Should Be Known   
    Taxile Doat is one of my favorites too. He came from the Sevres Porcelain factory in Paris at the invitation of Adelaide Robineau who's the Editor of Keramos and founder of the Syracuse National which established the collection at the Everson Museum. Robineau and Doat worked together in St. Louis at the University in the teens (1900 teens).
     
  8. Like
    glazenerd got a reaction from Rae Reich in What is in the commercial crystalline glazes?   
    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
     
  9. Like
    glazenerd got a reaction from Genboomxer in Another Newbie Playing with Native Soil   
    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
  10. Like
    glazenerd got a reaction from SuePeglar in My first kiln load with 3 macro crystal glazes   
    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.
  11. Like
    glazenerd got a reaction from SuePeglar in Crystalline Glaze Chemistry   
    Crystalline Glaze Chemistry
     
    Several have inquired about this specialty glaze in recent months, so I thought I would post an introduction into crystalline chemistry. The very first thing to do with this glaze is: throw out your glaze calculator and UMF spreadsheet: they do not apply to this glaze nor can you bring it into unity.
     
    Basic  cone 6 through 10 crystalline recipe is:
    50% ferro frit 3110, 25% zinc oxide, 25% silica 325m, and a seeding agent (see later).
    ^ Lithium carbonate flux additions discussed later.
     
    This is the basic crystalline glaze recipe, regardless of what cone you are firing to. However, crystalline glaze requires high fluidity of the glaze, so a high cone five is the minimum temperature level. It can be fired under five, but it takes a fair deal of chemistry to achieve it; so perhaps later it will be discussed. The reason you see so much variation in this basic recipe is because so many variables effect its outcome. Most of the variations are artistic preferences being inserted to control crystal size, population, and growth patterns. Likewise, the wide variance in firing ramp holds are due to kiln size, crystal development, peak cone temperature, and in many cases because the kilns were never calibrated by using cone packs or pyrometers to adjust thermocouple readings. An example: a ramp hold is stated as 2002F, but that same temperature could be 1992 or 2018F in your kiln.
     
    Frit 3110 is the standard and most reliable frit used in the crystalline recipe. There are frits used such as Fusion Frit 644, and others. If Ferro Frit 3110 is not available in your region, then use the chemical analysis of 3110 as a guide to compare available frits. Match the chemistry of your available frit as closely as possible to the chemistry of frit 3110.
     
    50% of the basic recipe is frit, it alone makes up the glassy matrix of the glaze. Although silica is being added to this recipe, that silica addition serves a specific function other than being a glass former. Yes, the silica will add to the glass content, yet it is being added for feedstock for crystals to form. Frit is ground up glass that has already been melted at high temperatures; so the chemistry required to form glass in a glaze is not a consideration. Crystalline glaze requires a thick application of glaze, and crystals require a thick layer of molten glass to grow in. So lowering the frit level in this basic recipe also means you are restricting the glass level in which they grow. You rarely see the level of frit deviate from this basic recipe, and when it is adjusted: those adjustments are minimal. 
     
    Crystalline glaze or crystals are chemically known as zinc-silicate crystals. Crystals form an ionic bond between zinc and silica: which is why equal parts of each comprise the basic recipe. Yes zinc adds opacity to the glaze and silica is a glass former: but neither addition is present in the recipe for those reasons. Zinc and silica are added and adjusted to form crystals, the additional glass formed or opacity added are secondary reactions. So the adjustments you see in various recipes are to manipulate crystal growth and population, and secondary “glaze chemistry†is not a consideration.
     
    Nerd (TJA 2017) 
    Edit 8-12-2017 for spacing and grammar.
    Edit 8-13-2017  Explanation of temperature in first paragraph amended.
  12. Like
    glazenerd got a reaction from SuePeglar in Crystalline Glaze Chemistry   
    Silica additions are used to control crystal growth, and like zinc when you hit a certain minimal level: development drops off. If you want to keep crystal population low, and their size smaller; then silica additions should run around 14-16% of the recipe. If you want to grow larger crystals, then additions between 18-22% are commonly used. Increasing silica additions are also used to control crazing in this glaze, which is notorious for crazing due to its chemistry. Do not concern yourself with controlling crazing issues until you have adjusted the recipe to suit your personal taste.
     
    Titanium dioxide is the seeding agent used to nucleate crystals. The black specks you see in the B&W photo below are tiny specks of TiO2. Most often I only use 0.10% of titanium to seed my glaze, and that is all that is required. However, you often see recipes calling for nearly 10% of titanium, or other additions such as rutile or ileminite that are both high in titanium. These additions are used for other reasons other than nucleation of crystals. Most commonly they are used to alter color, but more so because reduction firings are planned after the primary glaze firing. These levels of titanium are used to produce a purple color in reduction firings later on.
     
    Lithium carbonate is used as the primary flux in crystalline glazes. Lithium, silica, and zinc all have hexagonal crystal lattices on an atomic level. Secondly, lithium has a much lower molecular charge than zinc or silica, and therefore does not interfere with the ionic bonding required to produce zinc-silicate crystals. This molecular balance is most often described in articles on crystalline glazes as; “lithium has an affinity for zinc and silica.†The other fluxes that are compatible in crystalline glazes are calcium and boron. Both of these fluxes are added as secondary fluxes, and usually in very low levels. Many feel that small amounts of boron aids crystal growth, and I have found that to be true. Calcium is used more to produce a mottled background field in the glaze, more so than the typical use as a flux.
     
    Lithium additions are dependent on the peak firing temperature and the zinc variety used in the recipe. At cone six, 3% is used with white zinc, and 4% is used with yellow zinc. As the peak temperature rises, the lithium additions decrease. At cone 10, less than 1% is added and often none is used if a hold at peak temperature is incorporated in the firing schedule. Lithium additions are a balancing act: this glaze has to be fluid enough for crystals to form, but not so fluid that all of the glaze runs off into the catchers. So it is common to see lithium additions stated as 3.25 or 3.75; which only means that recipe has been dialed in to the peak firing temperature used by that potter.
     
    Firing schedules are broken down into two primary functions; the first being peak temperature used to melt any given recipe: the second being ramp holds at lower temperatures that actually grow the crystals. Almost all firing schedules seem to be vastly different from each other, and that is because of kiln size, kiln calibration (or lack thereof), and type of crystals being developed. Typically when a cone 10 peak temperature is being used, the corresponding ramp holds run between 1998F and 2032F. When cone six peak temperatures are being used, the corresponding ramp holds run between 1930F to 1976F.  These temperatures are highly generalized and are meant only to give you some sense of reference.
     
    Kiln size effects crystals, proximity to the elements effects crystals, and hot and cold spots within the kiln chamber effects crystal development. Sneezing while loading the kiln effects crystal development, they are very finicky little creatures. (pardon my humor) The fact of the matter is, it takes a considerable amount of time to dial in the best ramp hold temperature for your kiln: and every kiln will be different.  So start in the middle of the temperature ranges given above and move up or down from there. After you first test firing you produce spikes and clusters, make a ten degree downward adjustment in your ramp hold temperature. This should produce what are called “maltese†crystals, from there make 5 degree downward adjustments until round floret crystals form. Unless you like spikes or maltese crystals: then make no adjustments at all.
     
    All colorants used in crystalline glazes are metallic oxides: stains are not used and will not work to color crystals. Copper, cobalt, manganese, iron, and nickel are the most commonly used. Like most glazes, as you move up the ladder from low to high percentages, the depth of color increases. I would recommend you start with just copper and iron until you dial in your basic recipe. Both are reasonably predictable and much cheaper to use while testing. Once you dial in your basic recipe, then the sky is the limit in how you blend various colorants. It is very common to use multiple colorants to produce effects in this glaze, you can find all kinds of variations and their results online. Colorant additions gets into a rather complex explanation about how they interact with each other, so I will save that discussion for later.
    Clay: use only a good quality porcelain to start your crystalline journey on, it will produce the best and most predictable results. Crystals will grow on certain blends of stoneware, but you can explore that once you learn the basics.
     
    8-12-2017 Edit addition: Glaze application rate for vertical surfaces is typically 0.75 grams per square inch. Application for flat surfaces typically runs 0.50 grams per square inch. There are slight differences in the recipes if you are firing vertical or horizontal pieces. Lower zinc levels slightly on horizontal surfaces because none of the glaze runs off. Increase zinc additions on vertical surfaces because 20-30% of the glaze runs off into catchers.
     
    Enjoy the journey. 
     
    Nerd (TJA )
    Tom.... this will be the last technical post I make for awhile. my head hurts thinking about this stuff:)
     
    Edit 8-12-2017 for spacing and addition of glaze application rate information.
    Edit: 8-13-2017 opening comment on silica corrected, original was a bit confusing.
    Note: additional links to resources may be added to these posts in the future. They will appear as "edits".
  13. Like
    glazenerd got a reaction from Bill Kielb in My first kiln load with 3 macro crystal glazes   
    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.
  14. Like
    glazenerd got a reaction from Hulk in My first kiln load with 3 macro crystal glazes   
    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. Like
    glazenerd got a reaction from Hulk in My first kiln load with 3 macro crystal glazes   
    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. Like
    glazenerd got a reaction from JessHobbyPotter in My first kiln load with 3 macro crystal glazes   
    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.
  17. Like
    glazenerd got a reaction from Babs in My first kiln load with 3 macro crystal glazes   
  18. Like
  19. Like
  20. Like
    glazenerd got a reaction from MFP in Who wants to see an explosion, look here!   
    It's official: you are now a veteran potter.
  21. Like
    glazenerd got a reaction from Marcia Selsor in Important Ceramic Artists Who Should Be Known   
    My personal favorite- Taxtile Doat. - most crystalline glazers count him as the godfather of this speciality glaze.
    http://history.ucpl.lib.mo.us/results.asp?search=Doat%2C+Taxile+Maximin%2C+1851-1939
    check out the 4 foot wide porcelain bowl he threw in 1910. 2 assistants turned the wheel. 
    Help found the University Pottery (University City, Mo.) 1910. Proceeds funded the Woman's' Sufrage Movement.
    Teachers - he also wrote some of the earliest curriculum for Art Ed. 
    Have toured what is now called: University Museum.  
  22. Like
    glazenerd got a reaction from Bill Kielb in QotW: How do you feel about culture theft?   
    Been following this topic, but I know just enough about Japenese/Chinese/Korean culture to say something wrong. One of the many times I wish Baymore was around: these cultures were his speciality. Being a Westerner, I will add a twist to it.
     Modern technology has managed to put most of the worlds population onto a single stage/platform. The assimilation of culture that once took centuries, now only requires a mouse click. Marco Polo bought back porcelain pieces from China: and Europe spent 500 years trying to replicate them. Any potter can click Sung/Ming dynasty and start throwing in an attempt to duplicate it. The unfortunate side effect of instant knowledge, is the loss of culture and application.
     The old saying goes "imitation is the sincerest form of flattery."  Should the blog writer be offended or flattered that others are trying to imitate her culture?  Obviously some have hijacked strictly for ill advised sales promotions. Yet others love the work, love the culture, and are sincerely trying to imitate it.  Personally I think she should educate rather than reprove. It is a futile effort to chastise those who have no respect to begin with.
    thats my 5 cents  worth.  The extra 3 cents if for shipping and handling.
    Tom
  23. Like
    glazenerd reacted to Rae Reich in Giffin Grip 1984   
    In 1979, I paid $1000 for a catenary 12 cu ft hardbrick kiln and assorted shelves and glazes. 'Course, it had to be mapped, disassembled, hauled across town in an ancient pickup (stop loading when tires distort), bricks cleaned and reassembled. Oh, we were an energetic crew of potters and friends! 
  24. Like
    glazenerd reacted to Mark C. in Firing Schedule Variables   
    (Sorry Bill, I broke my two cup rule. Never answer questions until I finish the second cup.)
    if that coffee where stronger (fresh ground beans) only one cup would be nessacary.
  25. Like
    glazenerd got a reaction from LeeU in QotW: How do you feel about culture theft?   
    Been following this topic, but I know just enough about Japenese/Chinese/Korean culture to say something wrong. One of the many times I wish Baymore was around: these cultures were his speciality. Being a Westerner, I will add a twist to it.
     Modern technology has managed to put most of the worlds population onto a single stage/platform. The assimilation of culture that once took centuries, now only requires a mouse click. Marco Polo bought back porcelain pieces from China: and Europe spent 500 years trying to replicate them. Any potter can click Sung/Ming dynasty and start throwing in an attempt to duplicate it. The unfortunate side effect of instant knowledge, is the loss of culture and application.
     The old saying goes "imitation is the sincerest form of flattery."  Should the blog writer be offended or flattered that others are trying to imitate her culture?  Obviously some have hijacked strictly for ill advised sales promotions. Yet others love the work, love the culture, and are sincerely trying to imitate it.  Personally I think she should educate rather than reprove. It is a futile effort to chastise those who have no respect to begin with.
    thats my 5 cents  worth.  The extra 3 cents if for shipping and handling.
    Tom
×
×
  • Create New...

Important Information

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