🏺 Ceramic Glaze Calculator
Calculate glaze recipes using Unity Molecular Formula (UMF). Convert batch recipes to molecular formulas, analyze glaze chemistry, and adjust for different firing temperatures.
Glaze Recipe Builder
Materials (% by weight)
📊 Firing Cone Guide
Cone 06 (1830°F)
Use: Earthenware, low-fire
Flux: High (borax, frit)
Alumina: 0.2-0.3
Silica: 2.0-3.0
Common: Bright colors, frits
Cone 04 (1940°F)
Use: Earthenware, majolica
Flux: Moderate-high
Alumina: 0.25-0.35
Silica: 2.5-3.5
Common: Underglazes, decals
Cone 6 (2232°F)
Use: Mid-fire, stoneware
Flux: Balanced
Alumina: 0.4-0.6
Silica: 3.0-4.5
Common: Most hobbyist work
Cone 10 (2381°F)
Use: High-fire, porcelain
Flux: Lower, more refractory
Alumina: 0.5-0.7
Silica: 4.0-6.0
Common: Reduction firings
💡 Expert Tips from a Ceramic Artist
Test every glaze on tiles before applying to ware—one firing is cheaper than one ruined piece. Mix 100g test batch, apply to 3 tiles at thin/medium/thick application. Fire, observe gloss, color, texture, running. Thick application reveals if glaze runs; thin shows if it's too dry. I learned this after a "perfect" studio test glaze ran off 12 yunomi onto my kiln shelf at Cone 6, fusing them permanently. Chiseled them out, ruined the pots and shelf. Lost $250 in pottery and $80 shelf. Now I test everything on vertical tiles—if it runs at 35° angle, it'll destroy pots at 90°.
Glaze chemistry is more important than recipe percentages—different materials can produce identical results. A Cone 6 glaze with 0.3 K2O : 0.7 CaO : 0.5 Al2O3 : 4.0 SiO2 (UMF) will fire the same whether you use Custer Feldspar or G200 Feldspar, as long as final UMF matches. I've reformulated 20+ glazes replacing discontinued materials by targeting same UMF—fired identically. One student insisted they needed "this exact recipe" with Albany Slip (no longer mined). I calculated a substitute blend hitting same UMF using available materials—student couldn't tell the difference in fired results. Learn UMF and you're free from recipe slavery.
Alumina controls mattness—too much = dry/scratchy, too little = glassy/runny. For Cone 6: 0.4-0.5 Al2O3 = glossy, 0.5-0.6 = satin, 0.6-0.8 = matte. Beyond 0.8 gets chalky/underfired-looking. For Cone 10, add 0.1-0.15 to those ranges (higher temp needs more alumina). I formulated a "super matte" Cone 6 at 0.9 Al2O3—looked amazing on test tiles. Applied to actual bowls, it was so rough you couldn't eat from them without lip scraping. Reduced to 0.65 Al2O3, got beautiful soft matte that's food-safe. Always consider functional use when chasing aesthetics.
Silica ratio determines glaze durability—too low = soft glaze that crazes, too high = underfired. Cone 6 needs 3.0-4.5 SiO2, Cone 10 needs 4.0-6.0 SiO2. Below minimum, glaze has weak glass network (crazes, scratches easily, may leach). Above maximum, glaze doesn't fully melt (matte when you wanted glossy, or worse—dry patches). I had a Cone 6 glaze with 2.5 SiO2 that looked perfect but crazed within 24 hours every time. Bumped to 3.8 SiO2, all crazing stopped. For functional ware (dinnerware, mugs), err on higher silica side for durability.
Batch size matters—mix minimum 500g for tests, 2000g+ for production runs. Small batches (100-200g) magnify measurement errors. If you're off by 0.5g out of 100g, that's 0.5% error. In a 2000g batch, 0.5g is 0.025%—negligible. Also, small batches don't mix well—powder clumps differently. I mixed a beautiful turquoise at 150g test batch, scaling to 2kg for production yielded different color (less saturated). Turns out my 150g batch had uneven colorant distribution. Remixed 2kg batch more thoroughly, matched the test. For production, minimum 2kg gives consistent results and enough for 20-30 pots.
⚠️ Common Glaze Calculation Mistakes
❌ Not testing recipe totals add to 100%
The Problem: Materials add to 95% or 105% instead of exactly 100%, throwing off all chemistry.
Real Example: A potter wrote a Cone 6 recipe: 40% Custer Feldspar, 30% Silica, 20% Whiting, 15% EPK (total = 105%). They mixed it as-written, fired it, glaze was massively underfired and curdled-looking. Couldn't understand why—the UMF ratios looked right. Problem: they added 5% extra material, diluting everything. Recalculated to 38/28.6/19/14.4 (totals 100%), refired, perfect result. That 5% error changed Al2O3 from 0.52 to 0.55 and SiO2 from 3.9 to 4.1—enough to wreck the glaze.
The Fix: Always verify total = 100.0%. Use spreadsheet with auto-sum. If tweaking a recipe and materials total 98%, proportionally scale all percentages up. If 102%, scale down. Never fire a recipe that doesn't sum to 100.
❌ Substituting materials without recalculating UMF
The Problem: Swapping one feldspar for another 1:1 without checking molecular differences.
Real Example: A studio ran out of Custer Feldspar mid-production run, substituted G200 Feldspar at same 40% in recipe. G200 has more Na2O and less K2O than Custer. The glaze went from stable cone 6 to running off pots—Na2O has lower melting point than K2O, making glaze more fluid. They lost 18 bowls to kiln shelf fusion before catching the error. Difference: Custer has K2O:0.3/Na2O:0.07, G200 has K2O:0.1/Na2O:0.3—massively different chemistry despite both being "feldspar."
The Fix: When substituting, calculate UMF with new material, adjust percentages to match original UMF, test on tiles. Never assume "similar materials" are interchangeable without checking chemistry.
❌ Ignoring molecular weight in calculations
The Problem: Thinking weight percentage equals molecular importance in glaze formula.
Real Example: A beginner wanted to add "just a bit more calcium" to fix crazing, increased whiting from 20% to 25% (+5% by weight). Calculated impact: whiting is CaCO3 (100g/mol), while silica is SiO2 (60g/mol). That +5% whiting added proportionally more CaO molecules than equivalent silica would add SiO2, shifting UMF from 0.7 CaO to 0.95 CaO. Glaze went from satin to ultra-gloss runny mess. They thought "5% is small" but molecularly it was massive. Glaze ran off 8 mugs onto shelf.
The Fix: Always calculate molecular formula when adjusting recipes. Small weight changes in low-molecular-weight materials (ZnO=81, MgO=40) have huge molecular impact. Use glaze calc software or spreadsheets that track UMF as you adjust percentages.
❌ Testing glazes only at target temperature
The Problem: Firing test tiles only at Cone 6 (or target temp), missing how glaze behaves ±1 cone.
Real Example: A production potter perfected 12 glazes at exactly Cone 6 (2232°F). Kiln controller failed mid-fire, reached Cone 7 (2269°F) before shutting off. 140 pieces in the kiln: 6 glaze types ran off pots and fused to shelves (30+ pieces unsalvageable), 3 developed pinholes from boiling, 2 blistered, 1 looked same (only success). Total loss: $2400 in work plus $600 in shelf/post damage. If they'd tested each glaze at Cone 5, 6, and 7, they'd know which were temperature-sensitive and how to salvage firing accidents.
The Fix: Test every glaze at -1, target, and +1 cone. Note which have narrow melting range (dangerous) vs. wide tolerance (forgiving). For critical production glazes, test at ±2 cones to understand full behavior range. Temperature accidents happen—know your glazes' limits.
❌ Assuming colorants don't affect base glaze chemistry
The Problem: Adding 5-10% oxides/stains without considering they're also fluxes or stabilizers.
Real Example: A glaze base (Cone 6 clear) was perfect. Potter added 8% copper carbonate for turquoise. Copper is a strong flux—that 8% copper carbonate shifted the glaze's melting point down significantly. The "perfect" clear became a runny mess in turquoise, running into foot rings and fusing lids. Lost 12 lidded jars ($450 wholesale value). Base glaze had 0.52 Al2O3 : 3.9 SiO2. Adding 8% copper dropped effective Al2O3:SiO2 ratio by acting as flux. Should've reduced silica or added alumina to compensate for copper's flux effect.
The Fix: Calculate colorants into UMF, especially strong fluxes (copper, cobalt, manganese, iron). For >5% colorant, test on vertical tiles. Some colorants (chrome, tin) are refractory and stiffen glaze—adjust opposite direction. Track colorant effects in your glaze journal for future reference.
📖 How to Use This Calculator
- Select target cone: Choose firing temperature (06, 04, 6, or 10)
- Choose surface: Glossy, satin, or matte finish desired
- Add materials: Enter each material and its percentage by weight
- Verify 100%: Make sure all percentages add to exactly 100.0%
- Calculate: Get UMF analysis, chemistry breakdown, and recommendations
- Test on tiles: Always fire test tiles before applying to ware
- Adjust: Use UMF ratios to fine-tune glaze for desired result
Important: This calculator provides molecular analysis, but actual fired results depend on application thickness, clay body, kiln atmosphere, and cooling rate. Always test!
"Glaze chemistry separates potters who understand their materials from those who follow recipes blindly and panic when something goes wrong. Unity Molecular Formula is the Rosetta Stone of ceramics—once you learn to think in molecular ratios instead of weight percentages, you can reformulate any glaze, substitute unavailable materials, and troubleshoot problems systematically instead of guessing. I've seen too many potters waste years tweaking recipes by trial and error when a 10-minute UMF calculation would reveal exactly what's wrong. This calculator helps bridge that gap, but remember: chemistry predicts behavior, but testing confirms reality. Never skip test tiles."