Glazecalc

Glazecalc

Free glaze chemistry for potters. Enter a glaze recipe and see its unity molecular formula (UMF): the fluxes, alumina and silica it becomes in the kiln, and their ratio. Keep your recipes, materials, colorants, firing logs and notes together in one private notebook.

[glazecalcapp.com](https://glazecalcapp.com): try it without an account. A non-profit project by Aaron Filson, in 57 languages, and usable from AI assistants through its MCP server.

What it does

• Recipe to unity formula, as you type. Build a glaze from your own materials or the standard ones and watch its oxides in unity, grouped as fluxes, stabilizers and glass formers, with the silica to alumina ratio. That is how glaze chemists compare recipes, fix faults and substitute materials. Change the scale to percent, to the smallest whole parts, or to a batch in grams or in pounds (each shown in pounds and ounces), with colorants as a percent of the base, in parts or in grams; save a recipe and keep working on it, or open a saved one to change it.
• Compare two recipes side by side, oxide by oxide and by calculated thermal expansion, and try an old recipe with the modern materials that replace its discontinued ones (Custer Spar to G-200 EU), compared with the original. Where a swap is not like for like, it works the amounts out again, changing as few as it can, from materials sold in your region or any you add, and says what each one does and what to watch for past a recommended limit.
• Match with what I have: make a recipe again from only the materials on hand, a list kept with your account.
• Analysis and limits: the unity formula set against Hesselberth & Roy's stable glaze limits or Glazecalc's own, for the firing saved with the recipe, and a Stull chart of silica against alumina with its matte, semi-matte and bright regions.
• Specific gravity and water: weigh a measured volume of the glaze to find its SG, then the water that brings the bucket to the SG you want, or the water for a new batch.
• Paste in recipes from a website, a spreadsheet or your notes: see how each line was read and which material it was taken for before anything is saved.
• Blends for test tiles: two, three or four of your recipes blended into numbered tiles, with what to weigh for each and the chemistry of each tile.
• Cost per batch from the prices you pay, kept private with your account in one currency, and a mix ticket to print for the glaze room, with the batch number, the target SG and the materials' hazards (prices left off unless you choose).
• Share a recipe with a read-only link that anyone can open without an account, with its unity formula and how it is worked out, step by step; stop sharing at any time.
• Sign in with Google, GitHub or Microsoft, or with a password, two-step sign-in or a passkey.
• Use it from your AI assistant: Claude, ChatGPT, GitHub Copilot, Cursor, Gemini and others can use the calculations through the Model Context Protocol (MCP) server at /mcp, and your own records once you connect them: apps sign in to Glazecalc's own OAuth server and you say yes (read only unless you also allow changes), or you make an access token for them. Connected apps shows what each one did, puts back what it moved to the Trash and revokes it; the Assistants page says how to connect one.
• Guides for new potters, sourced: glazing from first principles with a glossary, how to make a glaze, safe mixing and ventilation, pottery at home with children and pets, and firing a basic kiln with cones, kiln sitters and manual switches; and, in English, a companion to John Britt's free online Glaze Course that links his videos unit by unit with exercises to try; and, in English and Japanese, a six-session pack for teaching glaze calculation.
• Famous glazes, each a public page with its traditional recipe or historic analysis and a version from the materials sold where you live (İznik first, as history, with a lead-free version not yet test-fired).
• Specific gravity and water, with the dry materials' SG estimated from the recipe (or typed, or measured as the making-a-glaze guide shows).
• Lead off unless you choose it, and old lead glazes rebuilt without it: Replace lead keeps the glaze's silica and alumina and gives lead's work to boron and other fluxes, on a lead-free base frit sold in your region with up to four other materials chosen for it, or keeps the colour on a lead-free base.
• Print it for the glaze room: the whole recipe with its unity formula and analysis, or just a batch list to tick off while weighing, with a running total for weighing into one bucket. One page on Letter or A4; weights in grams, or in pounds and ounces as set in your account.
• Your region and your numbers: where you work sets numbers and dates as you write them (12,5 or 12.5 typed either way), °C or °F, Orton cones, SK cones (JIS R 8101) or firing by temperature, the standard materials sold there, and in the guides: who to call in an emergency for 72 countries, and for 41 of them shops that sell glaze materials, the closest materials sold there to those a recipe names and the workplace limit for silica dust, with food-contact limits for glazed ware for 42; each checked on an official or the shop's own page.
• Translated into 57 languages: an official language of every country of the EU (Bulgarian, Croatian, Czech, Danish, Dutch, English, Estonian, Finnish, French, German, Greek, Hungarian, Irish, Italian, Latvian, Lithuanian, Maltese, Polish, Portuguese, Romanian, Slovak, Slovenian, Spanish, and Swedish), Japanese, Turkish, Traditional Chinese, Korean, Simplified Chinese, Thai, Vietnamese, Indonesian, Arabic and Urdu (right to left), Hindi, Bengali, Tamil, Marathi, Kannada, Telugu, Gujarati, Malayalam, Punjabi, Odia, Nepali, Sinhala, Latin American Spanish, Brazilian Portuguese, Swahili, Amharic, Afrikaans, Hausa, Yoruba, Zulu, Igbo, Somali and Quechua, each at its own addresses (/de/recipe).

Translated by AI with a glossary per language from suppliers' catalogues, reviewed, and the safety text checked by translating it back; every translated page says so and links to a form to suggest a better wording.

Every piece of text is a message (Transloco with ICU plurals), and the guides are Markdown per language (how translations are made).

• Your own colors: light, dark or as the device is set, and six palettes named for glazes, each readable in both.
• A standard library of 182 materials and 37 colorants and additives, from manufacturers' data sheets (and, for ashes and historical native materials, published research), for the US, UK, EU, Australia, New Zealand and the other regions, each with its source and other names, and hazards where the data sheet gives them, each with its own public page in every language. Discontinued materials stay for old recipes, each pointing to its modern replacement. Count colorants in the unity formula or leave them out, to compare with other calculators.
• Your own materials, from a chemical formula or a supplier's analysis, and colorants and opacifiers on top of a base glaze.
• A studio notebook: firing logs (times, temperatures, cones), notes, and plain-language advice on mixing, glazing and firing.
• Try it now: the whole app works as a trial with a generated name such as "speckled quiet kilns". Creating an account keeps everything; trials are removed after 14 days.
• Light and dark mode, from phone to desktop. Free and open source.

Highlights

For anyone reading the code:

• A 2017 AngularJS app rebuilt as Angular 22 (standalone components, signals, no zone.js, strict templates) and a TypeScript server on Express 5, Mongoose 9 and Node 24, which runs the .ts files directly with no build step (ADR 8), and put back online. The case study tells how.
• Tested at three levels, in CI on every pull request and push to master: about 1,000 server tests (98% of statements) run against the app in-process; over 700 Angular unit tests (92%); about 175 Playwright browser tests, including axe accessibility checks of every page in light and dark mode, every page in a pseudo-locale to find text not marked for translation, and every page in each language at a phone's width.
• One glaze chemistry library for the browser and the tests, checked against values worked out by hand (ADR 4).
• Keyless deploys with approval: GitHub Actions gets short-lived AWS credentials through OIDC, for a role that can only run one SSM command document on this app's instance. There is no SSH, there are no stored AWS keys, and a failed health check rolls back (ADR 2).
• Production for about $13 a month: one Graviton EC2 instance with Docker Compose, nginx and Let's Encrypt, a content security policy with subresource integrity, nightly backups to S3, snapshots and alarms (ADR 1, ADR 3).
• Careful accounts: bcrypt; HS256 tokens with a version, so changing the password signs out every device, kept in an httpOnly, SameSite=Strict cookie with a cross-site request check; hashed single-use reset links sent through Amazon SES with DKIM, SPF and DMARC; rate limits; ownership checks on every query; the current password to change the email or delete the account (ADR 5, ADR 6).
• Two-step sign-in and outside providers: passkeys, authenticator apps and recovery codes (ADR 14); Google and GitHub linked by the provider's id, never silently by email (ADR 15); Microsoft by tenant and subject (ADR 23).
• AI assistants as first-class clients: a stateless MCP endpoint sharing the app's recipe tools (ADR 17, ADR 19), Glazecalc's own OAuth authorization server (ADR 24), and changes from an app that wait for the person's yes (ADR 25).
• A translation pipeline for 57 languages: Transloco with ICU messages and the language in the URL (ADR 13); per-language glossaries sourced from suppliers' catalogues, staged reviews, blind back-translation of the safety text, and a plain notice for languages AI translates less well (process); `npm run check:i1