Library: Subsituting Gerstley Borate
INSIGHT Video Tutorials
Details how to substitute Gerstley Borate for another boron source in the popular Floating Blue glaze recipe. The lesson demonstrates that the most practical way to deal with the GB issue is on a glaze-by-glaze basis, formulating an approach that maintains the chemistry of the glaze, evaluates the sources of boron in the light of the chemistry of GB but also its physical properties and their importance to the working properties of the glaze. The boron sourcing frit (Ferro Frit 3134) is tried first and proves to be unsuitable, then ulexite is employed and found to be an ideal substitute.
Lesson 6: Substituting Gerstley Borate in Floating Blue
Gerstleyborate.com, when frits are not suitable, ulexite, using phantom, static and added status with colorants and retotaling and static materials
Substituting Gerstley Borate in Floating Blue
Welcome. I am going to talk about substituting Gerstley Borate for another material in the popular floating blue glaze recipe.
Also Gerstleyborate.com, when frits are not suitable, ulexite, using phantom, static and added status with colorants and retotaling and static materials.
Gerstley Borate has been a popular ingredient in raw glazes for many years. At digitalfire.com we author a website about this at gerstleyborate.com.
Recently it has gone through various perplexing cycles of becoming unavailable, then available again. More frequent changes in its behavior have accompanied this. The artware and pottery worlds have thus been absorbed in the pursuit of a substitute.
There is an better alternative. You can use INSIGHT to remove GB from your glazes and supply the lost oxides from other materials.
Floating blue glaze recipe
I will demonstrate replacement using the popular Floating Blue cone 6 glaze (this recipe has its own detailed page at gerstleyborate.com). I will replace the GB with another boron sourcing material.
I am going to be mentioning some techniques using INSIGHT that might not be totally clear unless you have watched some of the previous lessons.
Enter and duplicate the recipe
I have made sure the Lessons materials table is selected.
And have keyed floating blue into recipe 1 (I have left out the iron, cobalt and rutile, I am going work with the colorless base only).
Now I am going to click here to duplicate it into recipe 2 and make sure I have both recipes set to RO Unity calculation.
Replace Gerstley Borate with frit 3134
I have also removed the Gerstley Borate from recipe 2 by making sure its line was selected and clicking the line delete button.
I have also selected the next blank line in the recipe and added the same amount of Frit 3134.
Now if I click the MDT button to open the materials dialog you will notice that
With this frit is a good choice
This frit contains no alumina, thus I can source alumina from kaolin to suspend the glaze. I need to think about this because it was the natural claylike nature of Gerstley Borate that kept the original glaze in suspension.
But this frit is not working
At first this frit seems like it could work. But it brings a lot of extra sodium so the nepheline, which is currently supplying the bulk of this, has to be dropped to compensate. This will create a balance that makes juggling the materials to match the oxides quite complex.
Notice I have also checked the KNaO box.
Turkish Ulexite is better
A better solution is to choose a material of more similar mineralogy and chemistry to Gerstley Borate. This is the substitutes page at GerstleyBorate.com.
Turkish Ulexite is imported into North America and other continents in large quantities for use the fiber glass industry.
If I click here I will be taken to a detail page at the Digitalfire Reference Database.
Let's try this ulexite.
Replacing GB with ulexite
I am going to replace the frit with 20 units of ulexite. Notice I have cleared the Label and am about to click Update.
Planning a strategy
Notice that the CaO and MgO are now lacking and the KNaO is high.
If I add materials to source the former, the latter should be pushed downward. Why? Because this is a unity formula, INSIGHT recalculates the fluxes to total one, if I increase one the other amounts drop.
Notice also that the SiO2 and Al2O3 are high. Increasing the total amount of flux is going to force their amounts downward for the same reason.
Matching CaO, MgO with whiting, talc
I have added talc to source MgO and Whiting to source CaO. I played with the amount of each (by incrementing and decrementing) to get the closest formula match on a recipe amount multiple of 1.
Notice the KNaO is just a little high
Fine-tuning the new recipe
So now I will decrement the nepheline by 2 to match it up and then increase the kaolin by one to bring the Al2O3 back up to match.
Amazingly the silica does not need to be changed to adjust the SiO2.
Next, I am going to put the colorants into the recipe.
Assigning coloring oxides as phantom
Notice what happened here. When I entered this material I just typed cobalt ox assuming INSIGHT would find it in the materials database and expand the name. But this asterisk indicates that it did not find it. How do I know that? I can click here and this dialog explains what the status characters mean.
To get the name to look right I will edit this blank and update the line.
But that is not really a problem, I do not want coloring oxides in the formula anyway. So I am going to click this checkbox for these two lines and update also.
Using static colorants when retotaling a recipe
OK, these materials are not affecting the calculated formula anymore.
One more problem I want to deal with is this total. I would like to have a total of 107 and designate the coloring oxides as added materials.
But if I just recalculate to 107 the coloring oxide amounts are going to change. The solution is to first mark the three lines with static status. Static lines are ignored during retotal. Notice the new status characters.
Defining colorants as Added materials
I have chosen retotal from the Calc menu and specified 100 and then used Round Amounts in the Calc menu.
Here is the new total and the recipe. I should mention that the static status is not remembered with the recipe.
However added status is. I am going to set each of them as added using this checkbox, thus when I print the recipe they will be separated as such.
Fired samples: Improvements still needed
Take another look at the chemistry.
This glaze is very high in sodium and potassium and its calculated thermal expansion is likewise very high, that means crazing. However the high boron content appears to counteract this somewhat in practice. You can use INSIGHT to substitute some of the KNaO for another flux, but that might affect gloss.
Here are the fired samples. The Ulexite version has the same character, it just needs a cobalt/iron change for a little more color and a flow test to see if fluidity needs adjustment. The glaze slurry seems to work well also.
This is yet another example of a problem that can only be effectively dealt with on the chemistry level.
Many people have struggled with this problem but doing it this way was quite simple, dont you agree?
That is the end of this lesson.
Out Bound Links
In Bound Links
An example of how a glaze that contains too much plastic clay can shrink and crack during drying. This is raw Alberta Slip applied to non-bisqued samples.