Learn with John Britt's free glaze course

A companion to John Britt's free online Glaze Course on YouTube, unit by unit: his videos to watch, the Glazecalc guide sections to read, and exercises to try in Glazecalc.

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About this companion

John Britt is a potter and teacher who has made a free online Glaze Course: more than fifty videos on YouTube, from the unity formula to test tiles, clay and firing. The videos are his. They are free to watch on his YouTube channel, in the course's playlist. His website, johnbrittpottery.com, has his books and glaze notes, including two books published by Lark Books, now part of Hachette Book Group: The Complete Guide to High-Fire Glazes: Glazing & Firing at Cone 10 and The Complete Guide to Mid-Range Glazes: Glazing and Firing at Cones 4-7.

Glazecalc is not part of his course, and is not connected with him. This page only links to his videos, by the titles he gave them. It says nothing about what he says in them: watch them for that. What this page adds is what Glazecalc offers beside each unit: the sections of our guides that cover the same ground, and exercises to try with Glazecalc's calculator, or with an AI assistant connected to Glazecalc (how to connect one).

How to use it

  • Take the units in order, or pick the one you need. Some of his videos are numbered out of order; here they are grouped by subject.
  • Watch the videos first. They open on YouTube, and they are in English.
  • Then read the guide sections, and try the exercises. You need an account for the exercises that save a recipe, a blend or a firing log.
  • The exercises name the tools an assistant can use, such as analyze_recipe. In an assistant, the prompt glaze_course_lesson sets up a lesson for a unit.

Several units are lab work: weighing and mixing dry materials, and firing. Before you mix anything, read the safe mixing guide: dry glaze dust is the main hazard, and a fitted respirator, wet cleaning and lids on containers are the habits that matter most.

Unit 1: The unity formula

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  1. Start a recipe with a simple glaze you have, and watch its unity formula change as you add each material.
  2. Open How the unity formula is worked out on the recipe page and follow each step with your recipe's numbers. Then work one material out by hand and compare.
  3. With an assistant: ask it to run analyze_recipe on the same recipe and explain each group of oxides in the answer.

Unit 2: Limits and the Stull chart

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  1. On the recipe page, set the recipe's firing, then look at the limits panel and the Stull chart. Where does your glaze sit, and does the line at the top say its chemistry fits its firing?
  2. Change the silica a little at a time and watch the point move on the Stull chart.
  3. With an assistant: ask it to run check_limits with the recipe and its cone, and explain each caution and the coneFit verdict.

Unit 3: The oxides and what they do

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  1. Open three materials in the library, such as whiting, a feldspar and a kaolin, and note which oxides each brings to a glaze.
  2. With an assistant: ask it to run get_material for each and sort their oxides into fluxes, glass formers and stabilizers.

Unit 4: Color in different base glazes

Colorants such as copper, chrome and manganese need the most care when mixing. Read Materials that need most care before you weigh them.

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  1. Save two base glazes as recipes, then copy each and add the same colorant to the copies. Compare their unity formulas: what differs in the bases (boron, zinc, magnesium, alkali) that might change the color?
  2. On Blends, make a line blend from a base to the same base with a colorant, and print what to weigh for each tile.
  3. With an assistant: ask it to run blend_recipes from the base to the colored base, or analyze_recipe on both, and compare.

Unit 5: Blending and testing methods

Lab work. Read the safe mixing guide first, above all Habits that matter most.

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  1. On Blends, set up a triaxial blend from three of your recipes, choose the number of rows, and print what to weigh for each tile.
  2. Fire the tiles, then save the ones you like as recipes from the drawing of the tiles.
  3. With an assistant: ask it to run blend_recipes with two or three recipes as the corners, and to say which tiles pass check_limits and which look off for the firing.

Unit 6: Test tiles and melt tests

Lab work. Read the safe mixing guide first. Set test tiles on a dish or a scrap of bisque, since a melt test is meant to run.

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  1. Give each tile a code, and write it in a note with the recipe, the clay body and the firing.
  2. After the firing, write what each tile showed in the same note, and record the firing in a firing log.
  3. With an assistant: ask it to run search_guides for "test tiles" and summarise what to write down for each tile.

Unit 7: Glaze slurry and application

Lab work. Read the safe mixing guide first, above all Cleaning, clothes and hands.

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  1. Weigh 100 mL of a glaze you have, then use Specific gravity and water on its recipe page to see how much water brings it to the SG you want.
  2. Save that SG as the recipe's target, so it is there the next time you mix it.
  3. With an assistant: ask it to run search_guides for "specific gravity" and explain the steps for your bucket.

Unit 8: Where recipes come from, and substitutes

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  1. Enter a recipe that uses Gerstley Borate on the recipe page and choose Try modern materials and compare. Compare the two unity formulas.
  2. Add the materials you have on hand, then use Make it from what you have to remake a recipe from only those.
  3. With an assistant: ask it to run suggest_substitutes on the recipe, then match_from_materials with the materials you have, and compare both with analyze_recipe.

Unit 9: Special surfaces

Some of these surfaces use larger amounts of colorants, or reduction firing. Read Materials that need most care and Venting the kiln first.

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  1. Enter a special-surface recipe on the recipe page and read its limits panel. Which cautions are the point of the surface, and which still matter? A surface for sculpture is not one for a mug.
  2. With an assistant: ask it to run check_limits with the firing and explain why the coneFit check may say it cannot judge some of these glazes.

Unit 10: Raw materials and geology

Digging and grinding rocks makes dust. Read The main hazard: dust and Respirators first.

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  1. If you have an analysis of a local rock or clay, add it as one of your own materials and use it in a test recipe.
  2. With an assistant: ask it to run get_material for a feldspar and a kaolin and compare their analyses with your own material's.

Unit 11: Clay and slip

These videos are about clay bodies and slips. Glazecalc works out glazes, not clay bodies, so this unit is for watching.

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Try

  1. Write down the clay bodies you use, with their firing range, in a note, and test every glaze on each of them.

Unit 12: Firing

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Try

  1. Start a firing log for your next firing, with columns for time, temperature and cones. A gas kiln's log can add columns such as Ox Probe, Damper and Primary Air.
  2. With an assistant: ask it to run convert_cone_temperature for the cones you fire to, in both scales.

One more video

John Britt's course also has a video on a subject some potters come to for personal reasons:

Sources