[Editor's note: print this document with a monospaced font (Monaco or Courier on a Macintosh) to have the graphs and tables appear in their proper format.] Continuation of previous file: It is time to update our records. ------------------------ Cone 10 Glaze -------------------------- RO, R2O R2O3 RO2 (Bases or fluxes) (Alumina-Neutral) (Silica - Glass-former) Mol. Eq. for Fluxes Mol. Eq. for Al2O3 Mol. Eq. for SiO2 Max. Lithium .2 \ .4 4.5 Max. Calcium .65 \ Max. Zinc .25 / Total Max. Magnesium .3 / (1.40) ___________ 1.00 ( <----Remember the fluxes should add up to 1.00) ----------------------------------------------------------------- We must now cut our fluxing oxides down to 1.00. The calcium content is very high, so we will drop .05 off of its molecular equivalents. Intuition suggests that zinc and magnesium can cause the glaze to melt late, muddy the colors, dry out the surface etc, so we can cut them down to produce the following unity formula of molecular equivalents: ------------------------ Cone 10 Glaze ------------------------- RO, R2O R2O3 RO2 (Bases or fluxes) (Alumina-Neutral) (Silica - Glass-former) Mol. Eq. for Fluxes Mol. Eq. for Al2O3 Mol. Eq. for SiO2 Max. Lithium .2 .4 4.5 Max. Calcium .6 Max. Zinc .1 Max. Magnesium .1 __________________ 1.00 Total ---------------------------------------------------------------- If we could fire our test glaze and then reduce a chip from its surface down to the smallest molecular size which would still include the correct relationship of fluxes, alumina and silica, that little atomic or molecular mixture would have the relationship which we have represented in our last set of glaze notes (above). Think of it as if you could focus in on a minute bit of the tiny molecular trace with an electron microscope and you might be able to make out some very faint parts in a particular relationship which would match those we have listed. _____________ ________________________________________________ | |/////| | | | | | | | | | | Li2O|/////| |_ _ _ _|_ _ _ _|_ _ _ _|_ _ _ _| | .2 |/////| | | | | | | | | | |_____|/////| |_ _ _ _|_ _|_ _ _ _| | ZnO |/////| | | | | | | |_.1__|/////| |_ _ _ ___ SiO2 4.5 ___ _ _ _| | MgO |/////| | | | | | | |_.1__|/////| |_ _ _ ___ _ _ ___ _ _ ___ _ _ _| |// CaO .6 /| | | | | | | | | | |///////////|___|__________________ ___ ___ ___ ___ _| ~~~~~~~~~~~~|#####|#####|####|####| | | | | | |#####|#####|####|####|_____________________________| Al2O3 .4 ----------------------------------------------------------------- A Graphic Image of the Parts (Molecular Equivalents) in our Glaze. (Please Note: This has nothing to do with real sizes or weights. In reality, the materials, when melted, would be mixed, helter-skelter in a glassy, amorphous, liquid-like mix.) ------------------------------------------------------------------ (Step 6.) Making a Chart Showing the Chemical Molecular Equivalents and the Raw Materials. or "Getting All of Our Ducks in a Row" The time has come for us to make the transition from the world of theory and chemistry to the real world of raw materials which can be found in nature. In order to this, we can line our molecular equivalents up across the top of our page and place corresponding raw materials down the side. Again, you will need the raw material information from the Ceramics Gopher at SDSU or from any of the ceramics texts. This works out best if you place the fluxes first then alumina and silica. You may find an easy order by keeping the low-melting fluxes to the left and working up through the middle and higher fluxing oxides. / Fluxes or RO,R2O Oxides\/ R2O3 \/ RO2 \ ----------------------------------------------------------------- Equivalent | Li2O | CaO | ZnO | MgO | Al2O3 | SiO2 | Material Weight | .2 | .6 | .1 | .1 | .4 | 4.5 | ----------------------------------------------------------------- Lithium carbonate | | | | | | | (slightly water sol.) | | | | | | | Li2CO3 74 | .2 | | | | | | ----------------------------------------------------------------- Notice that Lithium carbonate is a simple, single fluxing oxide, material (i.e. It is not combined with other fluxing oxides). We can use it to supply all of the Li2O in the fired glaze. Note also that the Carbon (CO3) in the raw material will fire out and the final glaze will reflect only the oxide relationship of the lithium. Li2CO3 --> Heat --> Li2O || \/ Carbon Notice we have listed its Equivalent Weight and we will need to know that in one of the final stages of the process. Let's continue: / Fluxes or RO,R2O Oxides\/ R2O3 \/ RO2 \ ----------------------------------------------------------------- Equivalent | Li2O | CaO | ZnO | MgO | Al2O3 | SiO2 | Material Weight | .2 | .6 | .1 | .1 | .4 | 4.5 | ----------------------------------------------------------------- Lithium carbonate | | | | | | | (slightly water sol.) | | | | | | | Li2CO3 74 | .2 | | | | | | ------------------------- 100% ---------------------------------- Whiting | | | | | | | (also called | | | | | | | Calcium Carbonate) | | | | | | | CaCO3 100 | | .6 | | | | | ---------------------------------100%---------------------------- Zinc Oxide | | | | | | | ZnO 81 | | | .1 | | | | ------------------------------------- 100% ---------------------- Magnesium Carbonate | | | | | | | (slightly water sol.) | | | | | | | MgCO3 84 | | | | .1 | | | -------------------------------------------- 100% --------------- Alumina Hydrate | | | | | | | Al2(OH)6 156 | | | | | .4 | | ---------------------------------------------------100%---------- Silica | | | | | | | (also called Flint) | | | | | | | SiO2 60 | | | | | | 4.5 | -----------------------------------------------------------100%-- | 100% |100% |100% |100% | 100% | 100% | ----------------------------------------------------------------- Before we move on, check to make sure you understand that we are using the fired or convenient formula to match the raw materials with the chemical molecular equivalents. The equivalent weight compensates for the altered formula as it is changed by the fire. Yet, in our simple (all too simple, I fear!) example the only changes we see are those of carbon as it is fired out of the glaze. ------------------------------------------------------------------ Raw Material Raw Formula (nature) Fired or Convenient Formula ------------------------------------------------------------------ Lithium Carbonate Li2CO3 ------> heat ------> Li2O Whiting CaO ------> heat ------> CaO Zinc Oxide ZnO ------> heat ------> ZnO Magnesium Carbonate MgCO3 ------> heat ------> MgO Alumina hydrate Al2(OH)6 ----> heat ------> Al2O3 Flint SiO2 ------> heat ------> SiO2 || || \/ Carbon ------------------------------------------------------------------ We are almost finished! (Step 7.) Molecular Equivalents X Equivalent Weight = Glaze Parts by Weight or (Now That We Have All Our Ducks In A Row, Let Them Multiply.) While we set our information in order in the form of our molecular equivalent to raw material chart we also recorded the equivalent weight for each raw material. It is time to use all of our information to move out of chemistry and into the real world where we can weight and mix the ingredients to make tests of our empirical work. Please move to the bottom of this copy of our last chart . ----------------------------------------------------------------- / Fluxes or RO,R2O Oxides\/ R2O3 \/ RO2 \ ----------------------------------------------------------------- Equivalent | Li2O | CaO | ZnO | MgO | Al2O3 | SiO2 | Material Weight | .2 | .6 | .1 | .1 | .4 | 4.5 | ----------------------------------------------------------------- Lithium carbonate | | | | | | | (slightly water sol.) | | | | | | | Li2CO3 74 | .2 | | | | | | ------------------------- 100% ---------------------------------- Whiting | | | | | | | (also called | | | | | | | Calcium Carbonate) | | | | | | | CaCO3 100 | | .6 | | | | | ---------------------------------100%---------------------------- Zinc Oxide | | | | | | | ZnO 81 | | | .1 | | | | ------------------------------------- 100% ---------------------- Magnesium Carbonate | | | | | | | (slightly water sol.) | | | | | | | MgCO3 84 | | | | .1 | | | -------------------------------------------- 100% --------------- Alumina Hydrate | | | | | | | Al2(OH)6 156 | | | | | .4 | | ---------------------------------------------------100%---------- Silica | | | | | | | (also called Flint) | | | | | | | SiO2 60 | | | | | | 4.5 | -----------------------------------------------------------100%-- | 100% |100% |100% |100% | 100% | 100% | ----------------------------------------------------------------- ----------------------------------------------------------------- Materials | Molecular | Equivalent | Portions by | | Equivalent | Weight | Weight | ----------------------------------------------------------------- Lithium carbonate | .2 | x | 74 | 14.8 | Whiting | .6 | x | 100 | 60.00 | Zinc Oxide | .1 | x | 81 | 8.10 | Magnesium Carbonate | .1 | x | 84 | 8.40 | Alumina Hydrate | .4 | x | 156 | 62.40 | Silica | 4.5 | x | 60 | 270.00 | ----------------------------------------------------------------- ----------------------------------------------------------------- Note: Take the Molecular Equivalent times the Equivalent Weight to get the Parts by Weight. (Step 8.) Total the Parts by Weight and Take that Total Into Each of the Parts to get a Unity Formula. With the 'Portions by Weight', you could weigh the amounts and mix up a glaze test, however, one more simple trick of math will make you start looking like a professional and give you a unity glaze recipe (One that adds up to 100) which will make later testing for colors or correcting flaws like crazing very easy. All we need to do is add up the 'Portions by Weight' and take the sum into each of the parts. It will look like this: ----------------------------------------------------------------- Lithium carbonate | .2 | x | 74 | 14.8 | Whiting | .6 | x | 100 | 60.0 | Zinc Oxide | .1 | x | 81 | 8.1 | Magnesium Carbonate | .1 | x | 84 | 8.4 | Alumina Hydrate | .4 | x | 156 | 62.4 | Silica | 4.5 | x | 60 | 270.0 | ----------------------------------------------------------------- Sum ------> 423.7 ----------------------------------------------------------------- (Round off the figures and move the decimal two places) 14.8 divided by 423.70 = .034930375 3.49 Lithium Carbonate 60.0 divided by 423.70 = .141609629 14.16 Whiting 8.1 divided by 423.70 = .019117299 1.91 Zinc Oxide 8.4 divided by 423.70 = .019825348 1.98 Magnesium Carbonate 62.4 divided by 423.70 = .147274014 14.73 Alumina Hydrate 270.0 divided by 423.70 = .637243332 63.72 Flint (Silica) ------------------------------------------------------------------ Unity -> 99.99 (or 100%) ------------------------------------------------------------------ (Step 9.) Test it in a Firing if you choose. Well, there you have it. A very simple example of the empirical formula at work to create a glaze. There are a number of major problems with our glaze, as you would discover if you chose to weigh out the chemicals and run a test through a cone 10 firing. (Remember, we placed some limits on ourselves to keep it as simple as possible in order to learn about the foundation for the basic process. You are probably asking yourself, "What is wrong with the glaze, it looks like most recipes". You are right, it does have the raw materials and the weights listed. It even looks more professional than many, because we took the time to work it around to equal 100 (Unity). Yet, it can be improved. Here are some suggestions: (a) If we could learn how to do the math which will be involved when we have two or more ingredients coming from the same raw material, we might be able to cut the number of ingredients down, or at least, introduce the chemicals into the melt using cheaper sources from nature. Raw material sources which contain more then one material usually enter the melting process earlier and more evenly. (b) The alumina, in part or in total, could be introduced in the form of clay. The clay would keep the glaze from settling out so quickly in the glaze bucket. The clay would also provide some additional dry coat strength, making the freshly glazed surface less dusty or chalky as it sits on the shelf waiting for the next firing. Of course clay would also help provide some of the silica which will be needed in the mixture. You may run a test of the glaze, just the way it appears here, however, in a later lesson, we will learn to use more complicated raw materials which will help us overcome some of the problems which resulted from choosing the simple, single material, oxides. As we end this lesson, some brief remarks concerning the process of testing a base glaze for color response. We did the work and have our glaze adding up to 99.99 (100.) In a situation like this, where they are one or two tenths lower or higher then 100, most of us just add or subtract a tenth or two for one of the ingredients. (Here, silica is in the largest quantity, so by adding one tenth to its total, we have no effect on the finished melt. The alternative is to round the numbers until the total comes to 100. 3.49 Lithium Carbonate -------> 3.5 3.49 14.16 Whiting -------> 14.2 14.16 1.91 Zinc Oxide -------> 1.9 or 1.91 1.98 Magnesium Carbonate -------> 2.0 1.98 14.73 Alumina Hydrate -------> 14.7 14.73 from 63.72 Flint (Silica) -------> 63.7 63.73 <-- (63.72) -------------------- ------ ------ 99.99 (or 100%) -->100.0 -->100.00 -------------------------------------------------------------- (Step 10.) Run Line Blends to Find its Color Response, Correct Flaws or Change the Surface. The advantage of working the formula around to equal 100 makes it very easy to run line blends in the next phase of testing. After the base glaze is tested and has proven to merit additional work, you will want to see what kind of color response it will yield. Each test can be thought of as a percentage relationship to 100 parts (Unity) in the base glaze. For example: A typical line blend for a base glaze test for color response to cobalt would look like this: Test # 1 2 3 4 5 6 7 8 Base Glaze 100. 100. 100. 100. 100. 100. 100. 100. Cobalt Carbonate .25 .50 .75 1. 1.25 1.50 1.75 2. Most of us would speed the line blend up a bit by making four simple tests of .25, .50, 1.,and 2. grams for each 100 gram lots. (You can always go back and test between the weights if you need a specific adjustment to the color between two tests.) We should note that it is very hard to get an accurate test of .25, or .50 grams. The logical way to test for very tinny amounts is to double both the base amount and the metal color oxide. So a test of 200 grams of base with one gram of cobalt would be the same as a test of 100 grams of base and 1/2 (.50) gram of the metal but the result of the larger quantities would be much more accurate if you are using a gram scale. Many of the standard texts for ceramics include varying suggested limits for metal oxides used to produce color in the melt. A quick glance at any of those charts will help you get started with the planning stage for color line blend tests. I have found the most productive limits for metal oxides for glaze color are as follows: Cobalt Oxide and Cobalt Carbonate 00.25% --------> 2% Red, Black, and Yellow Iron Oxide 1.00% --------> 11% Iron Chromate 1.00% --------> 5% Copper Carbonate and Copper oxide 1.50% --------> 6% Chrome Oxide 1.50% --------> 5% Manganese Dioxide 1.00% --------> 5.75% Nickel Oxide .50% --------> 3.50% Ilmenite 1.00% --------> 4.50% Rutile 1.00% --------> 10.00% Vanadium Pentoxide 4.00% --------> 9.50% Your best bet is to run two or three sample percentages distributed throughout the total range for each metal oxide, then after those tests come from the kiln, you can decide on the best use of your time in the next round of tests. Blacks result from the saturation of the glaze with metal, so try using two or three metals in quantities from 1% to 5%. Saturate Iron glazes usually have 8% to 10% added to the base. Iron becomes a more active flux in reduction and Manganese fluxes more in an oxidation firing. Try to avoid large quantities of cobalt. This will cause the glaze to become very fluid. Chrome and Nickel will dry and matt the glaze surface. Some of your bases will come from the first test firing with an acceptable matt, opaque white. Other glazes can be made white with tin, titanium or zirconium silicates. Tin is one of the most expensive choices for white, although it has a variety of soft and unique effects on other coloring oxides. The Zirconium silicates will usually produce a strong or harsh, "Bathroom Bowl" quality of white which works well as a uniform support for strong brush work contrast. The limits for most of the opacifiers are in the range of 5% to 11%. ----------------------------------------------------------------- Lets review the steps we used in this lesson: (Step 1.) Choosing a Maturation Temperature (Step 2.) Finding the Average Molecular Equivalents For Silica at Cone 10 (Step 3.) Finding the Average Molecular Equivalents For Alumina at Cone 10 (Step 4.) Choosing the Fluxing Oxides (Step 5.) Finding the Molecular Limits for the Fluxes (Step 6.) Making a Chart Showing the Molecular Equivalents and the Raw Materials. (Step 7.) Take Molecular Equivalents Times the Equivalent Weights in order to get the Glaze Parts by Weight (Step 8.) Total the Parts by Weight and Take that Total Into Each of the Parts to get a Unity Formula. (Step 9.) Test it in a Firing if you choose. (Step 10.) Run Line Blends to Find its Color Response, Correct Flaws or Change the Surface. ----------------------------------------------------------------- (c) 1994 Robert Fromme For educational use, only. -----------------------------------------------------------------