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The Online Glaze Calculator (short 'OGC') is free but requires login. It consists of four pages:

Calculator: The old version with utilities.

Calculator+: New version with Stull-Map, Recipe Upload and 'Designer'.

Batch: Version for Handy or small screen.
Calculates glaze properties for a recipe.

Formula: Version for Handy or small screen.
Calculates glaze properties for a formula.

The following description mainly refers to page Calculator+.

Enter Recipe

Select a material in the material selection field and accept it with Use selected. You may edit the material formula or enter a material directly. To do this, enter the name in the input field My Material and the Weight of the material to the right. The weight is given in grams, but you can use any other unit of measurement. Enter the molar formula in the table of oxides. If you don't know the molar formula, the OGC also takes analysis and automatically recognizes the data format!

Also enter LOI%. This is the Loss On Ignition, i.e. the weight proportion that escapes in gaseous form during fire. These are decomposition products such as CO2 and the crystalline bound water. LOI% reduces the effective weight of the material. As in the case of CaCO3, this can be quite a lot. If you entered the material as a molar formula, the Molecular Weight MW is also calculated immediately. The MW contains all the oxides of a material, including the volatile ones. In old recipes, the MG is sometimes given without LOI%.

Maybe you don't know LOI%, but have the volatile oxides. Then enter these values. The OGC always takes them into account first and uses them to calculate LOI%. So if you entered the volatile oxides explicitely, the value in the LOI% field will not be taken into account.

Are you looking for a specific material? Do it with Material Search.
Using the table Material Search you can search for:
- Material Names: It's useful if you don't know the exact spelling, because you just have to enter a short string of characters from the name.
- Regions, Types
- Substances with certain oxides or without certain oxides or both.
- Substances that are similar. You can use this to search for substitutes.
All the materials you use will remain in Last Used for a few months.
Last Used is your private database.

On page Material you can permanently upload material data and a description. This data is available to all users. In order to make spam or advertising more difficult, the upload feature is for new users released not until some time.

Once you've found the right material, click Enter Material to enter it into your recipe. Now the recipe display My Recipe opens. Here you can still change the amount of materials or normalize the batch amount to 100. You often bring the batch total to 100 because that's more convenient. But it is not necessary.

To calculate the glaze formula and Glaze Properties click Calculate Formula. The result is displayed in the table Formula.
Besides, the recipe is also shown in the Stull-Map. If you like the result, give the recipe a name and save it with Upload Recipe.
Upload Recipe is your private recipe collection. The OGC may delete recipes automatically if not used for a long time. If you want to store recipes durable upload them at site My Recipe.

Enter Formula

If you don't want to enter a recipe but want to start with a glaze formula instead, use the table Formula.
You can enter the glaze formula directly as Mol, Unity or Analysis and calculate the glaze properties. Here, too, the OGC automatically recognizes the data format.

Now click Calculate to calculate the Glaze Properties:
Cone, Cone Range °C, Cone Range °F, COE, Si/Al, Acids/ Bases, Mol%
The formula is also immediately positioned in the Stull-Map.

You can determine the temperature influence of the Additives. It is customary to state the weight of the additives as weight percentage compared to the batch weight with no additives.
Example: 5% additives for a batch of 100 grams gives a total of 105 grams.


The Stull-Map positions recipes according to their SiO2 and Al2O3 content, because these oxides are particularly important for the glaze properties. You can see right away whether the glaze is bright or matte, whether it cracks or doesn't run at all. You can change SiO2 and Al2O3 and immediately see how this affects the Glaze Properties.

All your saved recipes are shown numbered in the Stull-Map.
You can Recall or Delete them in the My Recipe selection field. To make things easier to understand, I have already uploaded two Test-Glazes. You can delete them.

You can also experiment with a De Montmollin-Fuse. Initially, it is positioned in the middle of the map and surrounded by a 3 x 3 grid. The grid is like a cursor that you can move with clicks on SiO2+- or Al2O3+-.
The 3 x 3 cursor actually contains 7 x 7 fields for 49 test-glazes.

Following 5 fields of the grid are particularly important:
The blue field is your current glaze, the 4 red fields I name Cornerglaze. Using the Cornerglaze you make line blends (test mixes). In the Stull-Map with Al2O3 on the x-axis is Cornerglaze 'A' top left where SiO2 is maximum and Al2O3 minimum. In the Stull-Map with SiO2 on the x-axis is Cornerglaze 'A' top left where SiO2 is minimum and Al2O3 maximum. And the three other Cornerglaze... well, yeah, you can guess.

The 4 Cornerglaze contain combinations of minimum or maximum amounts of SiO2 and Al2O3. Fine. Then you can mix all samples in between with different amounts of the 4 Cornerglaze.

Click Blend Table and look at the blends. If you want to mix sample 10, you take 20 parts 'A', 10 parts 'B', 4 parts 'C' and 2 parts 'D'. The amount of SiO2 and Al2O3 is thus continuously changed in the samples. Of course you want to be able to determine how big the differences are between the individual mixtures. That's what the Al2O3 Increment-+ and SiO2 Increment-+ buttons are for. Be sure to check out how Increment-+ affects SiO2 and Al2O3 in the Unity Formulas (UMF) of the samples. To do this press More. This expands the table to 7 x 7 and displays data from all 49 samples.

By the way, you can change the orientation of the Stull-Map by
clicking SiO2 <-> Al2O3.


A glaze formula is like the blueprint for a house. Once you have the plan, you can get the material and make it fit. That's exactly what you do with the Designer. This part of the program looks for substances that are suitable for your recipe or formula and helps with assembly.

You won't always want to make an entirely new recipe. You may want to reuse some substances and replace (substitute) others. Maybe you've changed the Molecular Formula slightly and want to adjust the recipe. Or you still have a large amount of a material that you finally want to use up. There are many uses for the Designer.

All the materials that the Designer has found are shown in the Analysis format in the material table. Materials that are in your private material collection Last Used are highlighted in red.

There is also an oxide highlighted in red in the material list. The red oxide completely fills up the corresponding batch oxide, limiting the usable amount of a material.
Observe the filling process in the bar chart. If the input field Material Usage contains 100, the red oxide is completely filled and disappears in the chart. All substances that also contain the red oxide are no longer available. If you don't want that, you can enter a smaller value in the input field Material Usage.
Example: A value of 50 means that a substance only fills the red oxide by 50%. Other substances that also contain the red oxide are then still available.
Because the materials that contain the most oxides are the first to fall off, it's a good idea to apply them first.

It may happen that the database does not contain enough material to fill up all the oxides. You can then enter your own material in the input field My Material. You can later upload the ingredient to the material database or save it in Last Used. The format of your material, Mol or Analysis, is also automatically recognized here.

The Designer gets SiO2 min./ SiO2 max. and Al2O3 min. / Al2O3 max. at startup from the Stull-Map. This data is displayed in the table Line Blends and you can edit it.

Maybe SiO2 and Al2O3 are not the reason for your investigations and you are interested in other oxides. Then you select other oxides in the 1. Oxide and 2. Oxide selection fields and change the minimum and maximum. If you don't need Cornerglaze at all but just want to calculate your batch (My Recipe), simply delete the oxides with a click on Delete. Then the program finds more useful substances, because of course more materials are suitable for a single batch than for 49 different ones. Don't choose min. and max. larger than necessary, because the further apart the limits are, the fewer suitable substances are found in the database. This is because all 49 batches are to be made of the same components because of the Cornerglaze. Only the amounts of the recipe ingredients are different. This saves you work.

There is no point in calculating more precisely than the available material data. It's also useless to fill up all the oxides with an accuracy of +/- 0.001 Mol. This only leads to an unnecessarily complex and expensive recipe.

But a good glaze should also be a simple and inexpensive glaze. Don't worry about the accuracy of the data. Later you will do a series of tests anyway and choose the most beautiful glaze. Then you will also get the optimal recipe with the optimal formula. In order to keep the calculation accuracy within reasonable limits, the input fields Material Tolerance and Clear Oxide if less minimum values ​​specified. For Material Tolerance the minimum value is 2%, that's pretty little. If your recipe contains many natural ingredients that you buy from different suppliers the differences will be much greater. Clear Oxide if less contains a minimum value of 0.001 Mol by default. Below this limit, the calculation is terminated. Assess the accuracy of your material data and set the limits as high as possible.

The OGC combines the oxides Na2O and K2O by default because they have similar properties. So instead of Na2O can K2O be used and vice versa. As a result, more usable substances are available. If you want to know exactly how the OGC calculates, you have to uncheck Na2O and K2O combined.

Calculated Batch

Now it's ready, the new recipe, it's standardized to 100 grams. But maybe you want exactly 1234 grams of dry matter in the glaze? Then enter 1234 in the input field and press Change Total. This will adjust the raw material weights to the desired batch weight.

Below the recipe you will also see the Unity (UMF) of the new recipe. Compare it to the Unity of the old recipe. Small differences are not important, but if there are large differences, you should investigate the reason.

Did the guide help you? Do you have any questions? Write it! Questions and suggestions from users help to improve the OGC. I'm also happy if you take the time to fill out the Survey form.

One more request: The Online Glaze Calculator is free and ad-free. It would be a small thank you if you help to make it better known and share it with your friends.



Choose a Montmollin-Fuse or Recipe


My Recipe



Cone       °C      °F      Si/Al        COE  
Unity (UMF)


   Al2O3 Increment

Al2O3: min. -0.03 max. 0.03

   SiO2 Increment

SiO2: min. -0.3 max. 0.3