How to Mix a Glaze From Scratch
So you have a glaze recipe. You've weighed out the ingredients, you have a bucket and some water. Now what?
Mixing a glaze from scratch sounds straightforward, and in most ways it is — but there are a handful of steps that experienced potters do without thinking about them, and that beginners often skip or get wrong. This guide covers the complete process: safety, equipment, mixing, sieving, and getting the consistency right before you ever dip a pot.
Safety First — and This Is Non-Negotiable
Before anything else: you need a proper dust mask for this. Not a paper dust mask. An N95 respirator (or better, a P100 half-mask) rated for fine particulate dust.
Many glaze materials — including silica, flint, and clay minerals — release fine particles when dry-handled. Crystalline silica (quartz and cristobalite) is present in silica and flint specifically, and is the primary lung hazard: inhaled over time, it causes silicosis, a serious and irreversible lung disease. Fine alumino-silicate dust from clays also carries risk. The safe habit is to treat all dry glaze materials as hazardous. The risk isn't from a single session; it's cumulative. Silica particles are microscopic and stay suspended in air long after you've stopped disturbing the materials. Ventilation alone isn't enough.
Every time you handle dry glaze materials, wear your respirator. Put it on before you open the bags. Don't take it off until everything is sealed and you've cleared the workspace.
Everything else in this guide is optional to do perfectly. This isn't.
A few more things worth noting:
- Work in a ventilated area — outdoors or with airflow. A garage with the door open is fine; a closed studio with no airflow is not.
- Clean up wet, not dry — wipe surfaces with a damp sponge; never dry-sweep glaze dust. Dry sweeping resuspends silica particles.
- Don't eat, drink, or touch your face in the glaze area. Wash hands thoroughly when done.
- Gloves are a sensible habit, particularly with colorant oxides like manganese dioxide, barium carbonate, and chromium oxide, which carry additional hazards beyond silica.
What You'll Need
You don't need much, but a few specific things make the process significantly easier:
- Digital kitchen scale — accurate to at least 1g. For test batches under 200g, 0.1g accuracy is worth having.
- Plastic bucket with a lid — size depends on batch; a 5-litre bucket handles up to about 2kg of dry material comfortably.
- Mixing tool — a sturdy stick works for small batches. For anything over 500g, a drill with a paint-mixing whisk attachment saves real effort and mixes more thoroughly.
- Sieves — a 60-mesh sieve handles most glazes. An 80-mesh sieve is useful for fine-detail or brushing work where a very smooth slip matters. You'll need a bucket to sieve into, not just a sieve sitting over nothing.
- Graduated cylinder (100ml) and a scale for checking specific gravity — see Glazes 101 for the full explanation of SG and why it matters.
- Marker and labels — you will forget which bucket is which.
- N95 respirator — as above.
Step 1: Decide Your Batch Size
Before weighing anything, decide how much glaze you're making. The batch size determines how much water you'll add and gives you a check on your weighing (everything should add up to your target dry weight).
Some sensible starting points:
| Batch purpose | Dry weight |
|---|---|
| Test tile — new recipe or colorant | 100–200g |
| Small test batch — one or two pots | 300–500g |
| Working batch — a full glazing session | 1,000–3,000g |
For a first test of any recipe, 100–200g is plenty. You'll learn what the glaze looks like, whether it applies well, and whether it's worth scaling up — without wasting materials or kiln space on a glaze you don't love.
To calculate the gram weight for each ingredient, multiply each percentage in the recipe by your batch weight, then divide by 100. A recipe ingredient listed as 40% in a 500g batch = 200g. The Reading a Glaze Recipe post covers this in full detail.
Step 2: Weigh Each Ingredient
This is the step that most affects your results. Glaze chemistry is sensitive — even small deviations from the recipe ratios can shift a glaze's surface, melt behaviour, or colour noticeably. Weigh carefully.
A few practical habits:
- Tare the scale between each ingredient. If you're adding directly to the bucket, zero the scale with the bucket on it, add one material, note the weight, zero again, add the next.
- Keep bags sealed when not in use — both to prevent moisture absorption and to contain dust.
- Note the total weight of dry materials before adding water. This is your check: if your recipe says 40 + 18 + 17 + 13 + 12 = 100, your 500g batch should yield 500g of dry material on the scale. Discrepancies over 2–3g suggest a weighing error.
For fine-grained materials that tend to clump — Gerstley Borate and Gillespie Borate are the common culprits — break up any lumps in the bag before weighing. Large lumps don't disperse reliably in mixing.
Colorant oxides and stains (cobalt carbonate, copper carbonate, iron oxide, manganese dioxide) are best weighed separately into a small cup before adding to the batch — not directly into the main bucket. These are typically the smallest quantities in a recipe, often 0.5–5%, so any spill or scale error affects only the colorant rather than the whole batch. Add the cup's contents to the water along with the other materials.
Step 3: Add Water — the Right Way
Add the dry materials to water, not water to dry materials.
This matters because adding water to a pile of dry glaze creates a cloud of airborne dust. Adding dry materials to a bucket of water (with you wearing your respirator and adding slowly, close to the surface) contains the dust and reduces the amount that goes airborne.
How much water to start with: a useful starting estimate is around 50–60% of the dry weight. For a 1,000g dry batch, start with roughly 500–600ml of water in the bucket, then add your dry materials to it. You'll adjust from there.
This is a starting point, not a precise formula — the right amount of water depends on the specific materials in the recipe, and you'll dial it in when you check the specific gravity in step 5.
Add materials slowly, distributing them across the surface rather than dumping them all in at once. Let each addition begin to absorb before adding the next.
Step 4: Mix Thoroughly
Once all dry materials are in, mix until there are no dry clumps visible. Then let it rest for five minutes and mix again. This allows absorbent materials (clays, bentonite, CMC gum if you've added it) to fully hydrate before you assess the consistency.
For small batches, a sturdy stick or an old spoon works fine. For anything over 500g, a drill with a mixing whisk is significantly better — it reaches the bottom of the bucket and creates a vortex that pulls unmixed material up from below. Hand mixing tends to miss the bottom layer.
After the second mix, the glaze should look uniformly opaque and move like slightly thick paint. If there are still dry-looking patches or visible unmixed powder at the bottom, keep mixing.
Step 5: Sieve the Glaze
This step gets skipped more than it should. Sieve every batch, every time.
Sieving removes:
- Lumps of partially hydrated material
- Unmixed clumps of fine clay (bentonite is particularly prone to balling up)
- Debris from the bags or workspace
- Large particles from materials like Gerstley Borate that don't disperse cleanly
Use a 60-mesh sieve for most glazes. Hold it over a second bucket and pour the glaze through, working it through with your gloved hand or a soft brush. For glazes with materials that clump badly, pass the batch through twice.
A few materials need special attention:
- Gerstley Borate and Gillespie Borate tend to form lumps that won't fully dissolve by stirring alone. For recipes heavy in these materials, break up lumps before weighing and use the 60-mesh sieve (not a finer mesh — the coarser weave is easier to push lumpy material through). A useful trick for particularly bad batches: pre-soak the Borate in a portion of the water overnight before adding the remaining materials.
- CMC gum (if you're adding it as a binder) should be pre-dissolved in hot water and added to the batch separately — adding the dry powder directly causes persistent gel clumps.
After sieving, give the bucket a final stir and you're ready to check specific gravity.
Step 6: Check and Adjust Specific Gravity
Specific gravity (SG) is the density of your glaze relative to water and is the standard way to measure and communicate glaze consistency. The full explanation — how to measure it and what the target ranges mean — is in Glazes 101. The short version:
| Application method | Typical SG target |
|---|---|
| Dipping | 1.40–1.50 |
| Pouring | 1.38–1.45 |
| Spraying | 1.35–1.42 |
| Brushing | 1.40–1.50 |
To measure: fill a 100ml graduated cylinder with glaze, weigh it, subtract the weight of the empty cylinder, divide by 100.
If your SG is too high (glaze too thick): add a small amount of water — a tablespoon at a time for small batches — stir thoroughly and measure again. Repeat until you hit your target. It's easy to overshoot, so go slowly.
If your SG is too low (glaze too thin): you've added too much water. The safest recovery is to leave the bucket uncovered and let some water evaporate — this can take hours or overnight depending on your batch size. Adding more dry material is tempting but disrupts your recipe ratios, so avoid it if you can.
This is the main reason to start with less water than you think you need and add more gradually: it's much easier to add water than to remove it.
Step 7: Label Your Bucket
Write directly on the bucket with a permanent marker, or stick a label on:
- Recipe name
- Date mixed
- Batch weight (dry)
- SG target
This sounds like unnecessary fuss until you have three similar-looking white buckets and can't remember which is the clear satin, which is the iron amber, and which is something you mixed eight months ago that you can no longer identify. Label everything, every time.
A Note on Wastewater
Don't pour glaze rinse water down a domestic sink or drain. Many glaze materials — barium carbonate, cobalt, copper carbonate, manganese dioxide — are environmental contaminants that shouldn't enter the water system.
The studio standard: rinse your sieve, bucket, and tools into a dedicated settle bucket. Let it sit until the solids sink, decant the clear water carefully (this can go down a utility sink or floor drain in most cases), and let the settled solids dry out. Dried glaze waste goes in the regular bin, or can be fired as test glaze if you want to see what it does.
It's also worth discarding sieve residue — the lumps left in the sieve after straining — rather than returning them to the batch. They represent undispersed material that may not behave the same as the rest of the glaze.
Storing Your Glaze
A properly stored glaze keeps for months, sometimes longer. A few habits that help:
Always keep the lid on between sessions. This slows water evaporation and keeps debris out.
Stir thoroughly before every use — dense minerals (barium carbonate, zircopax, tin oxide) settle to the bottom and can form a hard cake if left long enough. Always re-check SG after stirring — water evaporates slowly even through a lid, and a glaze that's been sitting may have drifted higher than your target SG since you last used it.
Add a deflocculant to reduce settling. A few drops of sodium silicate solution, or 0.1–0.2% Darvan 7 by dry weight, helps keep materials in suspension longer without affecting the fired result. Start at the lower end — too much deflocculant can make a glaze feel thinner than its SG suggests, leading to thinner-than-expected application. This is particularly worth doing for glazes you won't be using frequently.
Glaze can go off — moulds can grow in buckets left for extended periods, particularly in warm conditions. If a glaze develops a foul smell or visible growth, it usually still fires correctly (organic matter burns off), but the glaze suspension itself may have been affected. When in doubt, sieve again before use.
Common Mistakes (and How to Avoid Them)
Mixing without a respirator. The consequences aren't immediate, so it's easy to skip — until it becomes a habit. Put the respirator on first.
Not sieving. The results: uneven application, blobs, and small crawling patches around lumps that melt differently from the rest of the glaze. It takes two minutes. Do it.
Over-watering, then adding dry material to compensate. If you add dry material back to a too-thin batch, your recipe ratios are off. The better fix is to let the water evaporate.
Not labelling. Every potter does this exactly once and regrets it.
Skipping the second mix. The five-minute rest and second stir matter. Clays and bentonite absorb water slowly — a glaze that looks mixed after the first stir often reveals unmixed lumps on the second.
Ready to apply? See Glazes 101 for how specific gravity relates to coat thickness, and Common Glaze Defects for what to do when something goes wrong in the kiln.