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About Hermes

  • Rank
    Advanced Member
  • Birthday 09/18/1948

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  • Location
    Holsbeek, Belgium.
  • Interests
    Metal machining, model making
  1. The major aim of my posts in this series is to emphasize on keeping records of all what you in the studio. I can assure you this is extremely helpful to learn and to increase ones experience. The posts started somewhat 'upside -down' with the intention to show that there is more than just keeping track of a recipe or a firing. Nevertheless, I repeat that everything related to your work is worth to be recorded. I use Filemaker Pro as the database system. For sure, there are other means. It depends what is useful and available for you. I try to put a screen dump of the main page (layout: 'Full Info') here. It is very big window and I need to scroll to see everything. The picture may by this be of low quality, sorry for that. The best is that I give a breakdown what fields are used and what they contain per record. Each record contains the full information of one ceramic piece. Fortunately, Filemaker allows to make different layouts, so that one can obtain a customized window with less cluttered fields. Fields Content Bisque number: I use unique numbers for each piece. The format is: yymmdd plus a suffix for each object of that day. Firing date: The date of the glaze firing Clay: The type of clay used Slip: The type of slip used if any Glaze: The glaze code Kiln type /program : Gas kiln or electric (with ramp program n°) Atmosphere : Oxidation or Reduction Reduction from : Temperature at which the reduction is started Glaze T°: Cone number at which the glaze is fired Cone T° range : If any, the temperature range in which glaze can be fired Re-fired : If the piece had to be re-fired: date Type: Earthenware, Stoneware, Porcelain, Raku Object description : Brief description of the ceramic object Glaze remark : Remarks on glaze: faults, appreciation... Original comment : If the glaze came from a book or elsewhere: the comment of the author General : General comment on the object: esthetics, faults, intended use, ... Source : Reference to the article or book where the glaze came from Score : (for fun) number of stars as appreciation from 0 (= destroyed) to 5 stars Glaze recipe (box): The glaze recipe with the colorants added separately Picture: Picture of the object Detail : Macro picture of glaze detail Firing diagram : As shown in part I Si/Al plot : As shown in part II Ternary plot : As shown in part III Limit graph : As shown in part IV Thermal expansion graph: As shown in part V INSIGHT Data general : Si/Al, SiB/Al, thermal expansion, LOI, ...from INSIGHT INSIGHT Chemistry : Unity formula, Limits and Molar % Further, there are knobs and links to shortcut to other layouts, databases ... Several fields contain drop-down menu's for easy completion. For multiple glazes applied on the object, tabs are provided to show the respective recipes My database contains over 500 records today. I hope this all helps to keep things organized and is helpful to increase the potter's experience. PS: From Wikipedia: Hermes was a god of transitions and boundaries. He was quick and cunning, and moved freely between the worlds of the mortal and divine, as emissary and messenger of the gods,[1] intercessor between mortals and the divine, and conductor of souls into the afterlife. He was protector and patron of travelers, herdsmen, thieves,[2] orators and wit, literature and poets, athletics and sports, invention and trade.[3] In some myths he is a trickster, and outwits other gods for his own satisfaction or the sake of humankind. So, girls and boys, think what you like... .... and.... For more information on glaze chemistry, visit my pages at: http://users.telenet...ics%20menu.html
  2. This time I will write a bit on the thermal expansion of glazes. The main causes of crazing and shivering are in the thermal expansion of glazes not being in equilibrium with the fired clay used. In the case of crazing, the glaze contracts more than the clay upon cooling and 'breaks' when the tension becomes too high. In the case of shivering, the reverse occurs and the glaze becomes 'to big' for the clay and splits off from the fired clay body. This can occur sometimes long after cooling, up to years. Obviously, the aim is to mix glazes so that their thermal expansion is in equilibrium with the fired clay. Again here, the book of J. Hesselberth and R. Roy ( Mastering Cone 6 glazes) is the reference for further reading. The authors spent quite a long article on this topic with plenty of practical experiments. How they measure thermal expansion is not meant for day by day potters but gives a good scientific proof for how glazes should be made up. As an important factor for the glaze quality and as an aid to learn more in the future, I use this parameter in the documentation of my ceramic work. Again, by the use of a glaze calculation software, the values for thermal expansion can be obtained. Also again, this can be obtained by calculating by hand, provided that one has the thermal expansion coefficient for each ingredient. The graph at the end of the text is a bit hybrid this time. It combine Si/Al ratio and thermal expansion. It also contains SiB/Al ratio. Boron has an exceptional behavior in glazes. In the unity formula it is grouped under Amphoteric but, it act as a glass former too. This makes it more complex. The SIB/Al is less a good indicator for gloss. I should maybe write: 'for matt' . The power for Boron to 'dissolve' Alumina is enormous. So, more glossy glazes are to expect. Some authors tend to classify Boron as a flux or as a glass former also. I keep the traditional Seger (unity) formula where Boron is an amphoteric (sometimes called: stabilizer). Although I am using Boron for ages in my glazes, I am still learning how to tackle its mechanism. Therefore, I keep record of the SiB/Al to gather data before drawing conclusions. Michael Bailey spent a whole chapter on the use of Boron in his book: 'Glazes Cone 6' (Ceramic Handbooks, A&C Black -London) To construct the bar chart, you obviously need the aforementioned parameters from a glaze calculation software or calculated by hand. We are coming close to the end of this series. Next time I will discuss how to put everything together in a database for documenting ones work. Visit my website for more on glaze chemistry: http://users.telenet.be/DannySpruyt/Ceramics%20menu.html
  3. Hi. Marcia answered and, I agree it might be confusing. I often thought to change that in my graphs when I was filling a record. But, for me also K an Na are behaving different so I leave it like it is. The trouble may be that Na OR K may get out of limit individually but when you sum up KNaO appears to be OK. Thanks for your interest, Hermes
  4. Many, many thanks for the support and the kind words! Hermes
  5. Thank you for your interest. I hesitate long before doing this. Our fellow member DocWeathers encouraged me to do so and he reviews part of my posts. My thanks go to him as well. Hermes
  6. In the previous post I treated the plotting of Fluxes, Amphoteric and Glass formers as a help and as an item to document ones work. With a little exaggeration, I can put that there are as many limit formula as there are authors on the subject. I stick to those mentioned by J. Hesselberth and R. Roy in their book "Mastering Cone Glazes". This range of limits is also available in the INSIGHT and other glaze calculation software. What is the use of these 'limit formulas'? As J.H. & R.R. put it: they are useful as guidelines, to make 'stable' glazes with the remark that one can make stable, good glazes who are way out of the limit formula. My definition of a 'stable' glaze is a glaze that: Has no glaze flaws like: crazing, shivering, crawling or dunting Is food safe when required Limit formulas can help but are not the universal panacea. Herewith the J.H. & R.R. Limit Formulas. They give the range of moles in the unity formula for the different oxides: Oxide range (Seger Unity) J.H & R.R. K+Na2O 0.1 - 0.3 CaO 0.2 - 0.6 MgO 0 - 0.3 BaO 0 - 0.4 (Cooper & Royle) ZnO 0 - 0.2 SrO 0 - 0.2 Al2O3 0.25 - 0.5 B2O3 0 - 0.3 SiO2 2.5 - 4.0 What you need is just the transformation of your recipe into the Seger unit formula. In glaze calculations software the limits are given next to it. So you don't need to make graphs, but I do. Graphs are more meaningful to me than just figures. It is a personal preference. In the example at the end of the text, SiO2 is divided by 10 to keep the graph in good proportions. The red marker lines show the limits. The glazes MC6G 1 and MC6G 2 are way out of limits for CaO and below limits for the alkalis. These are nevertheless reputed stable glazes. One can here also conclude they are Alkaline Earth matts. I document all my work with the topics mentioned in these posts, past, present and future. I repeat: For information on glaze chemistry, visit my website at: http://users.telenet...ics%20menu.html Next time I will discuss briefly thermal expansion and its role in glaze flaws.
  7. Thanks for your interest, for the reviews and surely to have encouraged me to post.
  8. I assume you have found out how it works. Just follow the tick marks for each group. The unusual thing is that they are inclined to an angle, that's all. Thanks for your interest
  9. In the previous post I discussed briefly the value of plotting Si/Al ratio in order to predict -with some reserve- the appearance of glazes. This time I like to show an example of a ternary or tri-axial plot based on the molar % of the glaze formula (in the analysis %). The reading of this kind of plot requires a bit of reflection but once figured out, it again adds interesting information on the glaze(s). The capability to predict the glaze appearance is somewhat less accurate than with the Al/Si plots, especially when Bore is used in the formulation. On the other hand I find that from scientific/technical viewpoint it helps to understand glaze chemistry. What you need is molar % of the used elements. If you have a recipe, you can calculate this by hand but, this is rather tedious. A glaze software like INSIGHT can give it in 1 or 2 clicks. Then the different Mol% of the metals are grouped in Fluxes, Amphoterics and Glass formers. When % are calculated for each group, these values can be entered in the ternary plot template. The template to make ternary plots is rather complex. I can provide it on request. An example is at the end of the text. In the example, WWW172 is likely to be a matt glaze, WWW390 has to rated as satin-matt and the other 2 glazes are probably glossy. Next time I will discuss the relative importance of limit values for the common elements used in glazes. We are still quite far away of 'putting things together ', be patient! In a few more posts to come, it will be revealed. For information on glaze chemistry, visit my website at: http://users.telenet...ics%20menu.html
  10. In the previous part, I explained the value of keeping record of all parameters in your ceramic work. The example given of a firing diagram is particularly valuable to master your kiln, especially if, like me, you use a simple, manually controlled gas kiln. Combustion kilns can be very 'moody' and therefore these recordings help you to get acquainted with your kiln. This time, I will briefly discuss and show one aspect of the glaze chemistry. Michael Baily's very interesting book "Glazes Cone 6" ( A&C Black -London / University of Pennsylvania Press) inspired me to adopt his viewpoints to predict the appearance of a glaze. From the unity formula, the (molar-) quantities of different ingredients expressed as oxides can tell you a lot. However, to make life easier, it is often sufficient to plot the Si/Al values in a graph and from where the plotted points appear, to obtain a good idea how your glaze may look. I am a chemist, but you don't need deep chemistry knowledge to make the graphs and to interpret them. The only thing you need is the Unity Formula or only the Alumina and Silica molar parts. In the example given here, one will discover that glaze B 123 is definitely an Alumina matt. Glazes B 210 and B 186a will be Alkaline Earth matts or, especially B 186a a satin - High Alkaline Earth matt. In turn, glaze B 215 will probably be a glossy gaze - on the edge of being satin. One has to be aware that those readings are approximations, as a lot will depend on how they are fired. Long or short holding periods, steep or flat heating curves, accidental reduction and many others may alter the results. Keeping this information for each ceramic piece you make will help you to refine your work. I recommend to go to my website and push the button 'Chemistry Ceramics'. It is a good introduction to ceramics and about its chemistry. (It is a quite big PowerPoint presentation) http://users.telenet...ics%20menu.html In Part III, I will briefly discuss Ternary graphs of Fluxes, Amphoteric and Glass formers.
  11. Keeping record of your work In literature it is often mentioned to keep record of all details of the ceramic work pieces. This is not a superfluous recommendation. It is the only way to progress and improve the quality of ones creations. On top, if you are interested in the chemistry of glazes like me, one can gather an impressive quantity of data that allows to understand better and better how complex glaze chemistry can be and,... it is fun! What to keep record of? Everything! There is no limit! Even to some extend, recording weather conditions can be of importance. Not that I am going that far... The minimum tool is a good notebook, kept in good order. Although this can be a sufficient tool, modern technology helps us to do it in an elegant and in a visually rich way. The main tools I use are INSIGHT for easy glaze calculation (this -or similar- can already be used as a good recording database) . I use Excel for making graphs of: · A firing diagram · Alumina/Silica ratio plots · Ternary graphs of Mole% of Fluxes, Amphoteric and Glass formers · Limit bar graphs based on the Unity formula · Comparative graphs of glazes with different thermal expansion All of the above are combined in a Filemaker database. As an example here is a picture of a firing diagram. It contains besides the temperature also the gas pressure and the damper opening during the firing. In a forthcoming post I will show some more examples of how it may look. Find more about ceramics on my web pages: http://users.telenet...Spruyt/Ceramics menu.html
  12. How I finish thrown pots The title has the intention to emphasize on how I finish pots. Perhaps it implies that not all what is described follows the orthodoxy of common knowledge. Throwing Since I leave the thrown pot on the bat for drying, I need a lot of bats. Advantages: · No risk of deformation or finger marks like can occur while cutting with a wire. · When almost leather-hard, the pot can be trimmed while still firmly fixed on the bat. · When leather-hard, the pot releases by itself and the bottom is still moist enough for further trimming. Disadvantages: · There is a very slight risk of cracking of the bottom. In my experience, I very rarely had that problem: only with extremely thin bottoms. · The drying occurs from top to bottom, whereas in the wire-cutting, the drying is more uniform. In my experience, it never caused a problem. I made bats from very durable. resin impregnated plywood used for concrete casting. This type of plywood can easily be found in DIY stores. My wheel is designed to accept notched bats. My bats are cut out using a jig-saw and a standard panel provides many bats. A corresponding notch is filed out to secure the bat on the wheel. Drying My drying shelves are wall mounted. This is not ideal as the air-circulation at the room side is different than at the wall side and thus, the pot may dry unevenly. To remediate that, I regularly give the bat (with pot) a quarter of a turn. Movable drying racks are preferable, but my studio is small. Trimming As mentioned, I sometimes trim the pot on the bat in the early leather-hard stage. But, where possible, I finish the wet pot just after throwing by removing the slip layer with a flexible rubber or thin stainless-steel rib. When I do it with care, I get an excellent finish making further trimming unnecessary. For the bottom part however, I pay special attention. Once it is releases from the bat, I trim the pot. Here I use the Giffin Grip™. I have different trimming tools, some commercial but several home-made. I try to keep my trimming tools sharp. I like Tungsten Carbide for trimming tools, but is (very) expensive ( http://www.bisonstudios.com/). My home made trimming tools are cut out of thin, bluish, blade steel ribbons that are used for securing heavy-duty packaging. The cut-out blade is bent into the desired form and glued into a wooden handle with epoxy glue. Near to the bottom part of the pot, I often trim a small 'gutter'. This helps to avoid runny glaze dripping on the kiln shelf. For very runny glazes such as crystal glazes, this is not effective. At the bottom itself, I always trim a recess. This forms a 'bottom ring'. The ring makes my pots be more stable. This detail improves the general 'feel of finish' of the pot. For larger bottoms like large dishes or platters, I leave an 'island' in the middle. This strengthens the platter if excessive force is put on it during its daily use (e.g. cutting food). I sign my pots with my full name and add an acronym for the clay type and an unique number. The latter is used for the full description of the pot in my database. Smoothing-up the dry pot If the pot still shows some unwanted marks, I smooth it with a scouring pad, middle-fine sanding cloth, or steel wool. I often use a Scotch Brite™ scouring pad. It gives good results especially when it is already a bit worn-out. In DIY stores they have pads for wood or metal. I have used both with good results. Post-bisque finishing (Before glazing) Sometimes I find bisque fired pots still not smooth enough. Particularly for crystal glazing, the smoother the pot the better the results. I also use it to obtain an egg-shell finish. When I use grog free clay, I use fine waterproof sanding paper in water where I have added a drop of dish-washing detergent. Of course, I let the pot dry thoroughly before applying the glaze. My pages on Ceramics can be found at: http://users.telenet...Spruyt/Ceramics menu.html
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