Glaze Batch Scaler: Parts, Percentages and Scale Modes with EPA Hazard Flags

A parts recipe uses relative numbers that sum to whatever they total. A recipe with 40 silica, 30 whiting, and 30 feldspar totals 100 parts, making the parts equal to percentages in this case. But a recipe with 80 silica, 60 whiting, and 60 feldspar totals 200 parts, and the percentage of silica is still 40 percent. The number in a parts recipe is meaningless except in relation to the total. A percentage recipe has already done the normalization: every ingredient is expressed as its fraction of 100 percent. Both formats contain the same information. This calculator accepts both and converts them correctly.

Many American glaze recipes list colorants as additions beyond the base 100 percent. For example, a recipe might say “EPK 20%, Silica 40%, Feldspar 30%, Whiting 10% PLUS Iron Oxide 5%.” The base recipe totals 100 percent. The iron oxide is an additional 5 percent calculated on top of that 100 percent. If you are making a 1,000-gram batch, the base ingredients total 1,000 grams, and you add 50 grams of iron oxide on top, making the final bucket 1,050 grams. This calculator handles additives correctly when you assign the “Additive” role to those ingredients.

Yes. In Percentage mode, this calculator normalizes any recipe where the base ingredients sum between 95 and 105 percent. It divides each ingredient’s percentage by the actual sum rather than by 100, ensuring the proportions are preserved even if a recipe copied from a book or database has a rounding error. If your total is far from 100 percent, say 78 percent or 120 percent, the calculator will show an error message because that likely indicates a data entry mistake rather than a rounding issue. Always verify that your base recipe sums close to 100 before any colorant additions.

Barium carbonate is regulated under the EPA’s Resource Conservation and Recovery Act (RCRA) as a hazardous waste because barium can leach from glazed ceramic surfaces and has been documented to reach hazardous concentrations in food and beverages. The Washington State Department of Health ceramics safety guide states explicitly that pottery containing barium from glazes must be disposed of as hazardous waste, not in regular trash. Unused barium carbonate powder is also treated as hazardous waste under these rules. Most contemporary US studio potters use strontium carbonate as a safer substitute when they need a similar flux effect.

The hazard is in the handling of dry cobalt carbonate during weighing and mixing, not in the fired glaze. OSHA’s permissible exposure limit for cobalt is 0.1 mg/m3 as an 8-hour time-weighted average, and NIOSH classifies cobalt as a potential carcinogen. When you open a bag of cobalt carbonate and measure 2.5 grams of it into your batch, you are handling a very fine blue powder that becomes airborne easily. Even a tiny amount of airborne cobalt dust can exceed OSHA limits in a small unventilated studio space. Wearing a properly fitted N95 or better respirator and working in a well-ventilated area eliminates virtually all the risk. The fired glaze, once the cobalt has fused into the glass matrix, does not leach at concentrations that present a health concern under normal use.

OSHA’s Respirable Crystalline Silica Standard (29 CFR 1926.1153 for construction and 1910.1153 for general industry) sets an action level of 25 micrograms per cubic meter of air and a permissible exposure limit of 50 micrograms per cubic meter as an 8-hour time-weighted average. Crystalline silica causes silicosis, an irreversible and sometimes fatal lung disease. Silica (SiO2) is the most common ingredient in most ceramic glazes. When you handle dry silica powder or flint without a respirator, you are inhaling silica dust. In a commercial studio, OSHA compliance is mandatory. In a home studio, the regulations technically apply to employees but not to the owner working alone. However, the lung disease risk is the same regardless of whether OSHA is inspecting. Always use a properly fitted N95 or P100 respirator when handling any dry silica-containing material, or use pre-wetted materials to eliminate the dust entirely.

The composition check uses the role you assign to each ingredient to track how much of your glaze by weight falls into each chemical category. It then compares those weight percentages against typical recommended ranges for the cone group you selected. A mid-fire cone 6 glaze that has 70 percent silica and only 5 percent flux is flagged because that silica-to-flux ratio is so imbalanced that the glaze will almost certainly be underfired and appear dry or sandy at cone 6. The check is a simplified assessment based on weight percentages, not a full Unity Molecular Formula analysis. Think of it as a sanity check for obvious imbalances, not a substitute for glaze chemistry software like Insight or Digitalfire for serious recipe development.

Yes. Select the “Low Fire (Cone 06 to 1)” option in the Orton Cone Range selector and the composition check adjusts its targets to low-fire chemistry, which typically requires more flux and less silica than mid or high-fire glazes. Raku glazes often have very high flux content to mature quickly in the raku firing process. The batch size calculation works identically across all temperature ranges. Note that many commercial low-fire glazes sold in the United States are proprietary premixed formulas and do not have published recipes in parts or percentages. This calculator is designed for recipes where you are mixing from individual raw materials.

FDA 21 CFR Part 109.16 establishes limits on lead extraction from ceramic food-contact surfaces into food and beverages. For flatware (plates), the limit is 3 parts per million. For small bowls and cups with volumes under 1.1 liters, the limit is 2 ppm. For large containers, it is 1 ppm. For mugs specifically, the limit is 0.5 ppm. These limits were developed based on health risk assessments and are enforced by the FDA. Any studio potter in the United States selling glazed functional ware should not use any lead-containing glaze material for pieces intended for food or beverage contact. Lead frits, sometimes marketed as “safer” than raw lead compounds, have been shown in acid leach tests to release lead at concentrations exceeding FDA limits. The only safe approach is to avoid lead compounds entirely in functional pottery.

Yes, that is exactly what Scale Existing Batch mode is designed for. Enter 1,000 as your original batch size, enter each ingredient’s gram weight in the amount field, and set the target batch size to 5,000g. The scale factor is 5.0, and every ingredient weight is multiplied by 5 automatically. This avoids any potential for math errors when scaling a large batch, and since it uses Big.js precision arithmetic, there are no floating-point rounding issues that could compound across 10 or 12 ingredients.

Chrome oxide (Cr2O3) in its green form is relatively stable and is regulated under OSHA’s Chromium VI Standard (29 CFR 1910.1026) primarily because of concerns about hexavalent chromium (Cr6+), which is a known human carcinogen. In most studio ceramics applications, chrome oxide presents a modest inhalation hazard during dry mixing that is managed with a respirator. The specific warning in this calculator applies to an additional concern: chrome oxide and tin oxide should never be fired in the same kiln load. When both materials are present in the kiln atmosphere at high temperature, they can produce chrome-tin vapors that affect nearby tin-glazed pieces, turning white tin glazes pink or gray. This is a glaze defect problem as much as a health issue, but both are real concerns worth flagging.

The calculator supports batches from 1 gram to 10,000 grams. However, very small batches below about 50 grams make it practically difficult to weigh small colorant additions accurately. If you are making a 50-gram test batch and your recipe calls for 1 percent cobalt carbonate, that is 0.5 grams of cobalt. A standard kitchen scale cannot reliably distinguish 0.5 grams. A jeweler’s scale accurate to 0.01 grams can. Glazy.org recommends a minimum of 100 grams for initial glaze tests, with 500 grams to 1,000 grams being more practical for testing application behavior on tiles. Once you have a confirmed working recipe from tests, scale up to a 5,000-gram production bucket using Scale mode.

The ingredient name field uses an HTML5 datalist containing over 50 common glaze materials used in US ceramic studios. As you type, your browser suggests matching materials from the list. When you select a matching material, the calculator automatically fills in the recommended role for that ingredient and triggers the hazard check. The autocomplete is helpful for common materials like “EPK Kaolin” or “Custer Feldspar,” but it is not an exhaustive database of every ceramic material available. If you are using a material that is not in the list, simply type its name and select its role manually. The hazard detection also runs keyword checks for common hazardous material names even if the exact name is not in the library.

Yes. After calculating, click “PDF Recipe Card” to generate a fully formatted PDF containing your recipe name, batch size, ingredient gram weights by type, the composition breakdown, any hazard warnings with specific regulatory citations, and the data source attribution. The PDF is formatted on standard letter-size paper and can be printed and laminated for the studio wall or stored in a recipe binder. Many studio managers in the US use this to document each batch with the date and source materials, building a production history that helps trace quality changes over time.

No. Commercial premixed glazes sold by Amaco, Spectrum, Coyote, and other manufacturers are proprietary formulas sold ready to apply after dilution with water if needed. They do not have published recipes in parts or percentages because the formulas are trade secrets. This calculator is designed for glaze recipes where you mix from individual raw materials like silica, feldspar, whiting, kaolin, and colorants. If you are using a commercial concentrate that is sold as a liquid or powder already formulated, follow the manufacturer’s mixing instructions and do not attempt to recalculate it through this tool.

Glazy.org and Digitalfire are glaze chemistry databases and Unity Molecular Formula (UMF) analysis tools. They calculate the oxide chemistry of your glaze at a molecular level, showing you the exact ratio of fluxes, glass formers, and stabilizers in molar terms. This is sophisticated ceramic chemistry software aimed at potters who want to develop new glazes from scratch or understand why a glaze works chemically. This calculator is a production batch tool: it converts recipes to gram weights, tracks EPA and OSHA hazard flags, checks approximate composition balance, and generates PDF recipe cards. You might use Glazy.org to develop a recipe and this calculator to mix every production batch of that recipe reliably.