A high-nepheline, zero-silica cone 8 silky matte glaze is cutlery marking and crazing. Why?
I will show you how found a recipe on Facebook, assessed it, substituted my own materials, tested it, adjusted it. Now it is like a cone 10 dolomite matte.
How I found a recipe on Facebook, substituted a frit for the Gerstley Borate and added the extra silica it needed to fight crazing. I got a fabulous cone 6 clear.
Using Insight-live I will demonstrate the surprising amount of silica some cone 6 base glazes that appear OK will accept and still melt well.
How to spot out-of-balance indicators in the chemistry of glazes that suggest susceptibility to scratching or cutlery marking.
Raw lithium carbonate can be replaced with a lithium-containing frit if you can do the chemistry. And you can at insight-live.com.
Use Insight-Live.com to do major surgery on a feldspar saturated cone 10R glaze recipe with multiple issues: blistering, pinholing, crazing, settling, dusting and possibly leaching!
The test bars will measure fired porosity and shrinkage over a range of temperatures, drying shrinkage, LOI and pugged water content. They follow procedures defined in Insight-live.com.
How to reference a picture from an external website like flickr.com from within a recipe in Insight-live
A short annotated video of how to create an account at insight-live.com
A short annotated video of how to sign-in to a personal account at insight-live.com
How to import the Digitalfire Insight recipe database file (INSIGHTDATA.DB) and the pictures that attach to recipes therein
Using help, your account, renewal and preferences pages, the managers and panels, recipes, materials, entering a recipe, chemistry, downloading desktop Insight.
How to find them, duplicate them and develop them within your account at insight-live.com
If your recipe is on the clipboard, this shows you how to import it into Insight-live and make adjustments after.
Learn how to add a recipe, title it, add lines and change them, set lines to added status, enter notes and pictures and print a mix ticket
An example of how to enter test results from your ceramic testing into recipes in your account at insight-live.com.
How to take a picture using an iPhone, crop and resample it, save it, then upload it to a recipe.
How to import data from desktop Insight, GlazeMaster, Matrix, GlazChem, HyperGlaze, Generic Spreadsheet CSV into your account at insight-live.com.
How to add and override material data and how to do chemistry calculations in your account at insight-live.com.
How to organize your recipes into a worksheet of recipe rows and material columns, save it as a CSV file and import into Insight-Live.com
A video tour of all the major features of the Digitalfire Insight-Live.com online recipe, material, test and picture manager.
A tour around the home page. Where to start.
I will show you some secrets of making a base engobe (or slip) apply to leather hard terracotta ware in a thick, perfectly even layer.
I will show you how to glaze a mug with a liner glaze inside and a colored one outside so that they meet in a perfect line at the rim.
To do a drop-and-hold firing you must manually program your kiln controller. It is the secret to surfaces without pinholes and blisters.
I will show you why people love/hate this material and how I substituted it for Ulexite to make a much easier-to-use glaze that fires just as good or better.
Making 10 gram balls of your glaze and firing them on 2in by 2in tiles is a great way to evaluate their flow, surface and susceptibility to defects.
I will show you why thixotropy is so important. Glazes that you have never been able to suspend or apply evenly will work beautifully.
D. Desktop Insight
Part two of a complete tour. It includes using targets, setting calculation types, entering recipe notes and details, SQLite and a review the menus.
Part one of a complete tour. The anatomy of the recipe window, how to open, edit and save recipes; the materials, oxides and supply oxide dialogs, the MDT.
Learn to how to download a recipe library from your account at Insight-live and open and explore it using desktop Insight
Compare calcium carbonate (whiting) with other sources of CaO (dolomite, wollastonite, frit), learn to understand the chemistry differences between materials and then substitute wollastonite for whiting in a specific recipe.
While comparing a real-world and theoretical feldspar learn to enter, edit, save, normalize recipes and the materials dialog. Glaze chemistry concepts.
Learn to do difficult formula to batch conversions. Learn mole%, finding frits by chemistry, Na2O sourcing, oxide oversupply, recipe line added status, overriding in the Supply dialog, when to compromise an exact match.
Learn to add a native volcanic ash to the INSIGHT materials database (MDT) and then create a glaze from it maximizing its percentage. Learn to impose an LOI on a material and why this method is better than line blending.
Learn to use a non-unity calculation to convert a formula into a batch recipe using theoretical and real-world materials. Retotal, round-off and make a side-by-side report.
Learn to convert a glossy glaze into a matte by comparing its chemistry with a target matte formula. Alter the chemistry in such a way that the thermal expansion does not rise and it maintains good physical application and suspension properties.
Learn what crazing is, how it is related to glaze chemistry, how INSIGHT calculates thermal expansion and how to substitute high expansion oxides (e.g. Na2O, K2O) with lower expansion ones (e.g. MgO, Li2O, B2O3).
Shows four different ways to add materials to the desktop Insight materials database (MDT)
Do this completely outside of Insight, it knows how to read it at each startup.
There are five ways to do it. Generate your MDT at digitalfire.com, copy and paste XML, type in the formula, enter an analysis as a recipe, handle the MDT as a CSV file in Excel.
Wollastonite is 50:50 CaO:SiO2. So why not just substitute 40 wollastonite for 20 calcium carbonate and 20 silica?
Learn to substitute Nepheline Syenite for Soda Feldspar (and vice versa) using the KNaO checkbox to. You will see the benefit of in-recipe substitution calculation rather than making substitution rules.
Learn the chemistry differences between cone 10 and 6 glazes and how to make a glaze melt at a lower temperature without introducing other problems like crazing.
Learn to reformulate a glaze that is settling in the bucket. Al2O3 and KNaO are sourced by the feldspar, we will source them from kaolin and frits instead.
How to use desktop Insight to substitute wollastonite for calcium carbonate (and vice versa) while maintaining the same SiO2 level. Create substitution rules.
Use Desktop Insight to explore ways of calculating substitutes for Gerstley Borate in the popular Floating Blue cone 6 glaze recipe while maintaining or improving the other raw and fired properties of the glaze.
How to fine-tune the thixotropy of a ceramic engobe for pottery
Tony Hansen takes you through all the steps from opening the box and wedging the clay to taking the fired mug from the kiln.
*Youtube Video, +MP4 Video, #ScreenCast, ^URL
Lesson 1B - Turning a Feldspar Into a Glaze
Learn to compare a target formula with the chemistry of a feldspar. See why it does not make a good glaze by itself and what materials need to be added to make it into a balanced glaze.
D. Desktop Insight
Click here to watch this at youtube.com or click here to go to our Youtube channel
Shows you how to consult a target formula and compare it with the chemistry of a feldspar to determine why a feldspar does not make a good glaze by itself and what materials need to be combined with a it to make it into a balanced glaze. You will get insight into why so many of the feldspar glazes in the public domain do not work well for some simple reasons.
Lesson 1B: Turning a feldspar into a glaze
Target formulas, feldspar chemistry, thermal expansion, supplying oxides to a formula from a material, getting detailed material and oxide information at digitalfire and oxide and material level thinking that technicians employ to make formulation decisions
Making a glaze from a feldspar
In this lesson I am going to make a glaze from a feldspar.
Well discuss using target formulas, feldspar chemistry, thermal expansion, supplying oxides to a formula from a material, getting detailed material and oxide information at digitalfire.com and oxide and material level thinking that technicians employ to make formulation decisions.
Formula & calculated items
Let's focus of the Formula List and Calculated Items list in the Recipe window.
Engineers have long studied formulas and their relationships to melting temperature, hardness, thermal expansion, gloss, resistance to leaching, color, etc.
This knowledge is well documented today, so we can use INSIGHT as kind of a crystal ball into the way glazes will fire in the kiln.
But INSIGHT does not think for us, it does the conversion from recipe to formula. We still need to interpret these numbers.
What should the oxide amounts be? Which oxides should or should not be here? How do they interact? We will answer these questions.
Open a target formula
mLets get started on answering those questions by continuing from Lesson 1A.
If specific oxides and oxide groups contribute specific properties to a fired glaze, it follows that the amounts of each need to fall within certain ranges to get a workable glaze.
Target (or limit) formulas basically show us these ranges.
I can open one to compare side-by-side with these formulas by clicking here.
Finding the targets
The recipe database window appears.
INSIGHT has searched the database for recipes having the word TARGET in the code number. I can do this anytime within this dialog by clicking this.
I have selected the Green and Cooper Cone 6 item and will click Open.
Targets of KNaO
Before continuing remember you need to have the lessons materials database selected here or your numbers will not match mine.
The target formula has appeared in column 3 in the Formula list. I have increased the width and height of the entire window and adjusted column widths of the formula list to display the target and two formulas properly.
You can learn more about limit and target formulas at digitalfire.com.
I am also going to click the KNaO checkbox. This will combine the amounts for K2O and Na2O since these oxides have similar contributions and almost all raw materials that source one also source the other.
Let's zoom in on the formula list.
Analyzing feldspar chemistry
Notice the K2O and Na2O totals are now combined.
By comparing the formulas of the two feldspars with this target it is evident that feldspar-as-a-glaze is lacking CaO (among other things) and has way too much KNaO. Almost all stoneware glazes have much more CaO than K2O/Na2O (to achieve hardness and resistance to leaching, but especially for resistance to crazing).
How could I know that? I will double-click the CaO line.
Learning about an oxide
The Oxide dialog appears.
Now I will click the Info button.
Now my web browser opens at the page at Digitalfire Reference Database website that tells me all about CaO and what it does in glazes and how it predominates as a flux in stoneware glazes and why.
Thermal expansion numbers
Notice also the expansion for theoretical potash feldspar in column one of the Calculated Items list.
This is really high. I use the INSIGHT standard set of thermal expansion numbers, over the years I have found that common stoneware glazes need to be below about 7.5 to avoid crazing. Of course your circumstances might be different, especially the clay bodies you use.
As an experiment try making a glaze from pure feldspar and fire it on a sample at cone 8 or 10, be ready for the worst crazing you ever saw.
Let me show you something else in the oxides dialog. I will double-click the CaO line again.
Comparing oxide expansions
mThe Oxides dialog appears again. Notice the thermal expanson of CaO, it is 0.148.
What does this number mean? Don't worry about it yet, just consider its relative magnitude. Higher numbers mean crazing, very low ones means that a glaze could shiver. Crazing is where the glaze is stretched on the ware and forms a network of cracks, shivering is where it is compressed onto the ware so much that it flakes off edges to relieve the stress.
Now, I will click the SiO2. Wow, that is more than 4 times lower. And Alumina. It is more than twice as low as CaO.
But now look at Na2O. It is more than twice as much as CaO, the highest of any oxide. So in a relative sense, CaO is a low expansion flux compared to sodium (potassium is also really high). That is why high-feldspar glazes often craze, they contain a lot of sodium and potassium.
The major raw sources of CaO in stoneware glazes are calcium carbonate and wollastonite (at low temperatures Gerstley Borate and frits are used).
How do I know that? It was near the bottom of that web page INSIGHT showed me a minute ago. We can see other materials that source alot of CaO here, one of note is Dolomite.
I will now add calcium carbonate (or whiting) to the Custer feldspar to bring it closer to being a glaze.
Calcium carbonate and wollastonite have different advantages and disadvantages as sources of CaO. What are they?
Finding whiting information
I have chosen Edit Materials in INSIGHTs Utility menu and the materials dialog has displayed.
I have clicked the list of materials and pressed the W key. This took me to whiting.
Now I will click the Info button.
Material info at Digitalfire Reference library
INSIGHT has opened to a page about Calcium Carbonate (which is whiting of course) at the Digitalfire Reference Library.
There is a link to Wollastonite also. And also to thousands of others materials right here.
Whiting into recipe
Now, back to the recipe window.
I have selected Recipe 1 and clicked the potash feldspar line and keyed whiting into Materials Lookup (in place of potash feldspar) and 10 into the Amount field. Click Update.
Line label override
However the recipe still says Potash Feldspar? This is because the Line Label was not changed. INSIGHT only uses the Materials Lookup field to find the chemistry, it displays the Line Label in recipes. When you create a new line INSIGHT automatically fills in the empty Line Label if not supplied. So to fix it I will remove the Potash Feldspar line label and click the Update button. INSIGHT will then copy Whiting from the Materials Lookup into it.
To learn more about the purpose and interplay between the label and lookup blanks see lesson 1A.
Whiting helps feldspar
Now I have clicked on the custer feldspar line, made sure recipe 1 was selected and entered 49 for the Amount and Updated, then I pressed the up arrow key to move the line cursor back up to line 2.
The Formula List shows feldspar by itself on the right and the whiting-feldspar combo on the left. With the whiting addition, feldspar is now very similar to the target formula. The silica, alumina and sodium/potassium are less than half of what they were and the CaO now dominates the fluxes (marked with asterisks).
Analyzing this mix
As you will see, in glaze chemistry we see materials as sources of oxides.
Could this two-material glaze work on stoneware at cone 10? Yes, at least it would melt very well. How about cone 6? No, a glaze with this high alumina needs a melter more powerful than CaO, for example boron from a frit. In addition, the thermal expansion is still much too high and crazing is virtually certain, the KNaO is way too high.
Also this two-material glaze has no kaolin or ball clay, that means it will immediately settle in the bucket and powder on drying. Clay is a perfect substitute for feldspar here because it also contributes lots of alumina and silica but not the expansion-increasing KNaO. I will leave it to you to finish this.
As you can imagine, doing all of this without INSIGHT would be difficult indeed.
Oxide and materials levels
The process of turning pure feldspar into a workable glaze in INSIGHT is a fascinating and educational one.
As you can see you need to think on both the oxide and materials levels. What do I mean by that? The formula determines the way the glaze fires, the recipe determines the way it performs in production of the ware. A third level is the mineralogy of the materials, understanding why they exhibit the physical properties they do.
Thus, chemistry is an important, but not the only piece in the puzzle of understanding glazes.
Out Bound Links
In Bound Links