# What is a Recipe?
Recipes are combinations of one or more ceramic materials. Recipes specify the proportion of one material to another. When mixed together, the recipe's materials form a new type of material- a clay suitable for throwing, a beautiful, shiny glaze, or a colorful underglaze.
The recipe below is a classic recipe called "Leach 4321". Leach 4321 is often used as an example because its recipe is very simple and it works well:
# Leach 4321
Because the recipe lists the proportion of ingredients, you can think of the amounts as percentages. Leach 4321 is a recipe made up of:
- 40% Potash Feldspar,
- 30% Silica,
- 20% Whiting, and
- 10% Kaolin,
For a combined total of 100%.
It is not unusual to see recipes that do not total to 100. Often, recipes in workshops are written down as batches rather than 100% proportions. For example, Leach 4321 can also be written as:
- 4000g Potash Feldspar,
- 3000g Silica,
- 2000g Whiting, and
- 1000g Kaolin,
For a combined total of 10,000g.
It's important to realize that this is the same recipe as listed above, just multiplied by 100 and specifying a unit of measurement. Potters often write down recipes in batch sizes that they work with to make mixing glazes easier. A batch size of 10,000g (like the one above) is often used when making up a large bucket of glaze or clay.
Note: All recipes are measured by weight, not volume!
# Recipe Basics
Learn how to bookmark, print, export, and make batches of recipes:
# Create a Recipe
Please see the Calculator section
- A quantity required for or produced as the result of one operation: made a batch of cookie dough; mixed a batch of cement. link (opens new window)
Because recipes list proportions of ingredients, no units of measurement are used. To make this recipe, you can measure in ounces or grams, even kilograms or tons!
For convenience ceramicists usually stick to the Metric System (opens new window). Batches of recipes are measured in grams and kilograms. Small test batches are usually only 100 or 200 grams, while batches for daily studio use can be 10 or 20 kilograms.
More information about mixing up batches: Mixing Test Recipes
# The Batch Calculator
Underneath each recipe listing is a Calculate Batch input box. After entering a number into this box, Glazy will calculate the total amount for each ingredient.
Here we calculate a batch size of 100:
And here we calculate a batch size of 200:
# Base Recipes & Additional Ingredients
Recipes are often divided into two sections: the base recipe and additional ingredients.
Imagine a recipe for pizza. The base recipe would include the ingredients for making the dough and sauce, while toppings like mushrooms and sausage would be listed as additional ingredients.
For glaze recipes, the base recipe is usually a plain glaze without any color. Additional ingredients like colorants and opacifiers can be added to change the look and character of the original base recipe.
Below is the same Leach 4321 recipe, but with an additional ingredient of 1% Red Iron Oxide:
# Leach 4321 Celadon
Notice that the name of this recipe has changed. Because this version includes 1% additive Red Iron Oxide, the type of glaze changes to a celadon.
Also notice that when calculating a batch, additional ingredients are added in addition to the batch amount. (The batch amount is actually the base batch amount.) So the total batch amount for this batch is 101, not 100.
# Recipe Information
Each Recipe has descriptive information, or metadata, that describes it.
In general, the more metadata is added to a recipe, the easier it is to categorize, compare, and search recipes.
Glazy uses highly structured data, meaning that instead of allowing users to define descriptive "tags" for recipes (like hashtags in Instagram), users are only allowed to select from a pre-defined, finite list of categories. Unfortunately, the names of these categories are currently only available in the English language. If you do not agree with a category, please contact Glazy and we can discuss changing it.
# Type and Subtype
Defining a useful, universal taxonomy for glazes is very difficult. Some of the recipe types and subtypes in Glazy were originally imported from old databases, while other types were inspired by John Britt's High-Fire Glazes (opens new window).
Glazy's recipe types are constantly being refined. If you have ideas to improve the system, please contact us.
Regardless of whether or not Glazy's system of types is adequate, when creating a recipe please specify a type and subtype. If glazes are categorized more specifically with subtypes like "Blue Celadon", "Black", and "Clear" then it is much easier for both the Glazy software and users to navigate the recipes.
There are currently only three status levels:
- Testing: A recipe that is not actively being used in the studio.
- Production: A recipe that is actively used in the studio.
- Discontinued: A recipe that is no longer used for some reason, for example an ingredient is no longer available or the glaze did not fit a clay body.
Only recipes with a status of Production are displayed in the default Glazy search page.
It can be useful to associate a recipe with a Country if the ingredients and firing are specific to a location.
For example, many traditional Chinese materials are tied to specific mine and kiln locations.
# The Unity Molecular Formula (UMF) Chart
# See Also: Unity Molecular Formula (UMF)
Each Glazy Search and Recipe page contains a Unity Molecular Formula (UMF) Chart. This chart shows the recipes closest to the current recipe. The current recipe is represented by a star symbol, while neighboring recipes are represented by a circle.
The UMF Chart defaults to a Silica (x-axis) and Alumina (y-axis) chart, which is the most commonly used type of chart when looking at glaze chemistry. But you can easily change the two axes to any combination of oxides.
# The Stull Chart
Overlayed on top of the UMF Chart is the Stull Chart. Here is the original Stull Chart, first published by R. T. Stull in Transactions of the American Ceramic Society, Volume 14, pages 62-70 (opens new window).
This is a slightly updated version of the Stull Chart which is a little more readable:
The Stull Chart has six regions:
- Unfused & Under-fired: Glazes in this region have either too much Alumina (Unfused) or too much Silica (Under-fired) are not fired to maturity.
- Matte: Glazes in this high-Alumina region are typically "true" matte glazes.
- Bright: In this middle-region, glazes are typically glossy glazes. Most of the recipes in Glazy, especially clear glazes, can be found in the Bright region.
- Crazed: Glazes in this region tend to have a crazed surface.
- The Stull chart was created for glazes with a flux ratio 0.3 R2O: 0.7 RO and fired to cone 11. There may be variations in the chart for glazes with different flux ratios fired at different temperatures.
- The Stull chart does not show or predict firing temperature. So, just because a recipe point lies in the "Bright" region does not mean it will be a glossy glaze at your firing temperature.
- Because crazing is a function of both the glaze and clay body, the Stull Crazing Region is highly dependent upon not only the glaze chemistry but also that of the clay body. So the Crazing Region will be quite different depending upon these factors.
- In spite of all these limitations, the Stull Chart Regions of Unfused & Under-fired, Matte, Semi-matte, and Bright still hold true at a number of different temperatures with a range of flux ratios and flux types. For futher information about how to apply the Stull Chart, please see the work of Matt Katz (some articles linked below).
Some of Matt Katz's research of the Stull: Introduction to Glaze Formulation Online (opens new window), Robust Mid-Temperature Glazes (opens new window) and How Glazes Melt (opens new window).
# Glazy Stull Chart
Due to space limitations in the website, the Glazy Stull Chart looks slightly different than the above chart, lacking the region names and color codings, but otherwise is the same. Each point on the chart represents a recipe. In this example you can see that most of the recipes fall within the Stull "Bright" region.
Each point representing a recipe has two color codings. The inner color of the point represents the R2O:RO Ratio, while the point outline represents the amount of Boron.
# R2O:RO Ratio
The R2O:RO Ratio Scale shown in the Stull Chart.
The color of each recipe point denotes its R2O:RO ratio. Recipes high in R2O are redder, while recipes low in R2O are bluer.
The ratio of R2O to RO oxides has implications for glaze stability and expansion.
Matt Katz has demonstrated that a 0.3 R2O: 0.7 RO ratio produces the most robust glazes at a range of temperatures.
# Boron Level
The outline of each recipe point represents the amount of boron. Recipes containing boron have an orange outline, and the thickness of the outline represents the amount of boron. Typically, glazes lower in temperature will contain more boron.
# UMF Chart Trends
The following charts show all public Glazy recipes for Low-Fire, Mid-Fire, and High-Fire. Three trends stand out:
- The vast majority of recipes fall within the Stull "Bright" region.
- As recipes increase in temperature, so do their Silica and Alumina levels (points are located higher in the chart).
- As recipes decrease in temperature, Boron increases (orange outline thickens).
# Stull Al/Si chart showing Leach 4321 analysis using different feldspars.
The following Stull chart shows the Leach 4321 recipe with different feldspar and kaolin analyses. You can see that by varying the types of ingredients (or the analyses of ingredients), the recipe will fall at different locations on the Stull Chart. It's good practice to use actual ingredients with the most accurate analyses possible, for example using "Custer Feldspar" instead of the generic "Potash Feldspar" or "Feldspar".
# Using the Glazy Stull Chart
This video shows the basics of how to use the Stull Chart in Glazy:
# Filtering the Chart
The chart can be filtered by using the form on the right. The recipe category can be changed (in the above screenshot, the category is Iron - Celadon - Blue), or the temperature can be filtered, or the axes of the graph can be modified.
The chart always loads as a plot of the oxides SiO2 and Al2O3
Because the Stull Chart is based on SiO2:Al2O3, it will disappear if you choose a different oxide pair.
# Show Images
By clicking the "Show Images" checkbox you can display the thumbnail photos for each recipe in the graph. Please note that many recipes do not have photos and will only display as a greyed-out square.
# Zooming in the chart
While the UMF Chart in the search can automatically be Pinched & Zoomed, the UMF Chart on the recipe page initially has Pinch & Zoom disabled in order to avoid accidental zooming.
Just click the "Allow Zoom" button to start zooming.
# Similar Recipes & Analyses
Introduction to similar recipes and analyses in Glazy:
# Similar Base Recipes
If two recipes consist of the same base materials (not including additional materials) in the same amounts (within 1%), then they are considered similar.
- Two Leach 4321 glazes (40% Feldspar, 30% Silica, 20% Whiting, 10% Kaolin) may be similar even if their additional oxides differ. For instance, Leach White is a 4321 glaze with added Zircopax, while Leach Celadon is a 4321 glaze with added iron. These two glazes are considered similar by Glazy.
- A Leach 4321 glaze recipe with 40% Potash Feldspar is similar to the same glaze recipe with 40% Custer Feldspar because the materials or their parent materials are the same.
- A Leach 4321 glaze recipe with 40% Potash Feldspar is not similar to the same glaze recipe with 40% Soda Feldspar because the materials (and their parent materials) are different.
- A Leach 4321 glaze recipe with 39.5% Feldspar and a Leach 4321 glaze with 40% Feldspar are considered similar because the material amounts only vary by %1.
# Similar Analyses
Two recipes are considered to have similar unity formulas if their oxides do not differ more than .05 For this comparison, K2O and Na2O are combined (KNaO).
Note: Recipes that have similar unity formulas do not necessarily exhibit similar fired characterisitics.
# Oxide Coloring
Oxides are colored by their role in the UMF. The role of an oxide may change depending upon whether you are viewing Traditional UMF or Extended UMF.
# Traditional UMF Coloring
R2O Group: Na2O, K2O, Li2O
RO Group: PbO, SrO, BaO, ZnO, CaO, MgO, MnO
R2O3 Group: Al2O3
B2O3 (Special Case)
RO2 Group: SiO2, ZrO2, SnO2, TiO2
Other Oxides: FeO, Fe2O3, MnO2, P2O5, F, CoO, Cr2O3, Cu2O, CuO, NiO, V2O5, ZrO, HfO2, Nb2O5, Ta2O5, MoO3, WO3, OsO2, IrO2, PtO2, Ag2O, Au2O3, GeO2, As2O3, Sb2O3, Bi2O3, SeO2, La2O3, CeO2, PrO2, Pr2O3, Nd2O3, U3O8, Sm2O3, Eu2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3
# Extended UMF Coloring
R2O Group: Na2O, K2O, Li2O, Bi2O3, CuO, SnO2
RO Group: PbO, SrO, BaO, ZnO, CaO, MgO, MnO, Fe2O3, MnO2, CoO
R2O3 Group: Al2O3, TiO2, NiO
B2O3 (Special Case)
RO2 Group: SiO2, ZrO2
Other Oxides: FeO, P2O5, F, Cr2O3, Cu2O, V2O5, ZrO, HfO2, Nb2O5, Ta2O5, MoO3, WO3, OsO2, IrO2, PtO2, Ag2O, Au2O3, GeO2, As2O3, Sb2O3, SeO2, La2O3, CeO2, PrO2, Pr2O3, Nd2O3, U3O8, Sm2O3, Eu2O3, Tb2O3, Dy2O3, Ho2O3, Er2O3, Tm2O3, Yb2O3, Lu2O3
# Exporting Recipes
Recipes can be exported as a Recipe Card- an image containing the recipe photograph, name, and recipe details.
Recipes can be exported to your favorite glaze calculation software. Currently, only Insight and GlazeChem are supported, but hopefully more export formats will be added in the future.
To export a recipe, simply select "Export" from the menu on the recipe page. The Recipe Card image can be saved on your computer or shared with others online. The downloaded glaze calculation software text file can be imported into your program.