Why Mixing Your Own Glaze Is Worth It
There is a particular moment, somewhere between the second and third bucket, when a grey slurry stops looking like a mistake and starts looking like a glaze. It settles into thin cream, you dip a test tile, and the kiln does the rest.
Most potters arrive here the same way. You have bought a few commercial glazes, loved two of them, and grown quietly tired of the price and the narrow palette.
Mixing your own changes both things at once. Raw materials are sold by weight, and a modest bag of frit, silica, and clay makes many litres of working glaze — far more volume than the same money buys in small jars.
A 500-gram batch, mixed to a dipping consistency, fills roughly a litre of working glaze. That is a season of small pots from one afternoon at the scale.
The control is the larger reward. Colour becomes a number you can turn up or down. Surface becomes a decision rather than a lottery: more clay for a soft matte, more flux for a glassy shine.
There is a cost, and it is honest. A glaze is a small recipe repeated exactly, so it rewards care and record-keeping more than inspiration.
That trade is the whole bargain. You give the bench an hour of attention; it gives you a surface that is genuinely yours.
What a Glaze Actually Is
A glaze is glass, thinned enough to melt at pottery temperatures and thick enough to stay where you put it. Four jobs have to be filled at once, and the balance between them is the recipe.
Silica, the glass former
Silica, usually quartz or flint, is the material that actually becomes glass. On its own it melts somewhere above 1,700°C, which is hotter than most studio kilns will comfortably reach.
So silica needs help. That help is the second job.
Flux, the melter
A flux lowers the melting point of silica into the range your kiln can manage. Borax-based frits are the beginner's friend: pre-melted at the factory, partly insoluble, and predictable in the bucket.
Feldspar, whiting, lithium, and zinc also flux, each in its own way and at its own temperature. Change the flux and you change the cone at which the glaze matures.
Alumina and clay, the anchor
Alumina raises the glaze's viscosity while molten, so it clings to a vertical wall instead of running to the shelf. Most of it arrives as clay — kaolin or ball clay — which also holds the powder in suspension.
Too little and the glaze runs off the pot. Too much and it sits stiff and dry, refusing to smooth out in the firing.
Colourants, the variable
Oxides and carbonates — cobalt, copper, iron, manganese, rutile — give depth and variation, and they shift with atmosphere and temperature. Commercial stains are pre-calculated blends that stay truer and repeat more easily.
Both work. Oxides are cheaper and more surprising; stains are steadier and kinder when you are chasing one specific colour.
Notice what is missing from that list: nothing here is decorative. Every ingredient is doing a structural job, and the colourant is the only one you can freely swap.
A Beginner's Base Recipe Structure
You do not need a famous recipe to begin. You need a proportion that holds together, and one colourant to test it with.
Here is that proportion in plain parts by weight:
- 50–60% frit or borax-based flux source
- 20–25% silica
- 15–25% clay, such as ball clay or kaolin
- 5–10% colourant, added on top of the base
The first three add up to 100%. The colourant is extra, counted as a percentage of the base. It is a small distinction that prevents a great deal of confusion later.
A 500-gram batch might be 275 g frit, 110 g silica, and 115 g ball clay. A 5% colourant addition would then be 25 g, weighed on its own dish.
Why frit rather than raw borax? Frit has already been melted and ground, so part of it resists dissolving in the bucket water. The slurry stays more consistent from one session to the next.
This is a starting point, not a promise. It sits in the low-fire region, around cone 04 to 06, and it still has to be tested on your clay with your kiln.
Measuring by Weight, Not Volume
Every glaze in every book is written in parts by weight, and for one reason: powders do not pack the same way.
A cup of silica and a cup of frit can differ by a third in actual mass. Clay settles and compacts in the bag. A humid week changes the scoop again.
Volume measuring turns a repeatable recipe into a hopeful guess, and the kiln is unforgiving about guesses.
Use a digital scale that reads to 0.1 g and has a tare button. Set the empty bucket on it, press tare, and add each material in turn, taring between additions.
Weigh the colourant last, into its own small dish. Strong colourants such as cobalt are easy to over-add and impossible to remove once they are in.
Work over a shallow tray so spills stay contained, and clean with a damp cloth rather than a dry brush.
Water and the Specific Gravity Test
Powder plus water is not yet a glaze. The proportion of water decides how much material stays on the pot in one dip, which is why potters measure it instead of eyeballing the bucket.
Add water slowly and stir until the glaze looks like thin cream. Then test its specific gravity — the weight of a set volume of glaze compared with the same volume of water.
Here is the method:
- Weigh a small cup empty. Say it reads 12 g.
- Fill it to a marked 100 ml with water and weigh again. At 112 g, the water weighs 100 g.
- Empty and dry the cup, then fill to the same mark with well-stirred glaze.
- Weigh. At 157 g, the glaze weighs 145 g.
- Divide: 145 ÷ 100 gives 1.45.
Aim for roughly 1.4 to 1.5 for dipping. Below that the glaze is watery and the coat too thin; above it the coat builds fast and may crawl or pinhole.
Thin with a little water, thicken by leaving the lid off or stirring in dry base, and always stir properly before measuring. Glaze settles — the top of the bucket is not what you dipped yesterday.
Write the number in the notebook. It is the single most useful measurement in the whole process.
Sieving and Slaking
Once the powders are weighed and wet, let the bucket stand overnight. This is slaking: the clay particles hydrate fully and the mixture becomes uniform.
In the morning, stir well, then pour the glaze through an 80-mesh sieve into a second bucket. Work it through with a soft brush rather than forcing it with the stirrer.
Sieving catches the lumps that would otherwise pop in the kiln and leave pinholes, along with grit and stray material from the bag.
Rinse the sieve back into the bucket, never into the sink. A second pass is worth the five minutes for glazes with a high clay content.
Label the bucket now, while you still remember exactly what went into it.
Test Tiles and the Line Blend
Never glaze a real pot with an untested recipe. Make tiles instead, from the same clay body, rolled to an even thickness, and bisque fired as usual.
Write a number on the underside of each tile in pencil or underglaze pencil before you start. Without numbers, five brown tiles become five anonymous brown tiles.
A line blend is the simplest test that teaches you something. Mix one base, then add increasing amounts of a single colourant:
- Tile 1: base, no colourant
- Tile 2: 1% colourant
- Tile 3: 2%
- Tile 4: 3%
- Tile 5: 5%
For strong colourants such as cobalt or chrome, halve those numbers. For iron or rutile you can comfortably double them.
Fire all the tiles in the same firing, on the same shelf, as the work they are meant to predict.
A flat tile tells you what a glaze looks like; a textured one tells you how it behaves. A tile pressed with lace or coarse cloth — the same principle as slab lace imprinting — shows exactly where glaze pools in the hollows and breaks thin over the ridges.
That is the information you actually need before committing a bowl to it.
Thickness is its own variable. Make a second set and dip twice, and you will see how much of the colour came from the coat rather than the percentage.
Firing Temperature and Cone Ranges
Potters talk in cones because a cone measures heat work — temperature held over time — rather than one thermometer reading at one moment.
Roughly: cone 06 to 04 is low fire, near 1,000 to 1,060°C. Cone 5 to 6 is mid fire, around 1,200 to 1,240°C. Cone 9 to 10 is high fire, near 1,280 to 1,305°C.
A glaze is balanced for one of those ranges. Fired too low it stays dry and under-melted; fired too high the flux keeps working and it runs off the pot.
So follow one rule above all others: do not mix recipes across cone ranges. A cone 6 recipe with a handful of low-fire frit stirred in is no longer a cone 6 recipe.
Witness cones on each shelf tell you what your kiln actually did, rather than what the controller believed. Place them where you can see them through the peephole.
Keep low-fire and mid-fire materials on separate shelves, in separate buckets, with the cone written on every label.
If your kiln fires to cone 6, choose cone 6 recipes and test them there. A frit-based low-fire base is the gentler starting point when your kiln is small.
Safety at the Bench
The real hazard in glaze mixing is not the finished glaze. It is the dust.
Silica powder, breathed in repeatedly over years, damages lungs. The practical answer is simple and unglamorous: keep it out of the air.
- Wear a fitted respirator when handling dry materials — a proper P2 or P100 mask, not a loose paper dust mask.
- Mix in a ventilated space, away from the kitchen, and away from children and pets while powders are open.
- Clean up wet. A damp cloth or wet paper towel beats a dry brush that lifts dust back into the air.
- Never pour glaze or rinse water down a household drain. Let the bucket settle, pour off the clear water, and dry the sludge for solid waste.
- Label every bucket with recipe, colourant percentage, cone, and date. An unlabelled bucket is an unknown, and unknowns get treated carelessly.
- Keep food and drink out of the glaze area, and wash your hands before you leave it.
None of this is exotic. These are ordinary studio habits, and they become automatic within a week.
Glaze on skin dries to a fine dust and then flakes onto the bench. Wash hands and forearms before they dry, and never let a child handle a dripping glaze brush.
Store powders sealed and out of reach, and keep a small brush and dustpan that never go back to the kitchen.
If you are mixing while small children are awake, do it in a closed room and clean before they come in. Powder on a floor is the part that gets missed.
Record-Keeping, the Quiet Skill
A glaze you cannot repeat is a happy accident, not a recipe.
Keep one notebook and write the same things every time: date, base recipe in grams, colourant and percentage, water added, specific gravity, sieve size, clay body, bisque cone, firing cone, and the result.
Tape the tile to the page, or photograph it in daylight. A note saying "nice blue" will not help you in six months.
Record the failures just as carefully. A crawling tile with its numbers attached is more useful than a pretty one with none.
This is the part beginners skip and later regret. It is also the part that turns a hobby into a body of work.
Troubleshooting Common Faults
Most glaze faults come from four things: thickness, dust, firing, and proportion. Work through them in that order before you change the recipe.
Crawling
Crawling shows as bare islands of clay where the glaze pulled back into beads. The usual cause is a coat applied too thickly, or a dusty, oily bisque the glaze could not grip.
Wipe bisque with a damp sponge and let it dry. Thin the glaze slightly, dip once rather than twice, and fire more slowly through the early stages.
Pinholing
Small craters that never heal over. Often the glaze is too thick, the bisque still holds dust, or the kiln climbed too fast and trapped gas beneath a surface that sealed early.
Try a thinner coat and a slower start to the firing. Sieving again rarely hurts anything.
Running off the pot
A glaze that flows past the foot is over-fluxed, over-thick, or over-fired. Check the cone first, then the specific gravity, then the recipe.
Wipe the foot clean, leave a margin above it, and fire on a catch tile so a run does not weld the pot to the shelf.
Muddy or dull colour
More colourant is not more colour. Past a certain point cobalt goes grey-blue, copper goes flat, and iron goes dense and dark.
Contamination is the other suspect: a bucket used for iron will tint every pale glaze afterwards. Keep separate buckets for iron-rich and pale glazes.
Then check the firing. A colour developed in reduction looks entirely different in oxidation, and no amount of mixing will change that.
Your First Successful Batch
The first batch that comes out right is quieter than you expect. No drama — just a tile with an even coat and a colour that reads the way the notebook said it would.
Keep that tile. Keep the page. The next batch is easier because you know what the numbers mean now.
From there, change one thing at a time: a little more clay for a softer surface, a different colourant, a second dip.
That is how a palette gets built. Not in one inspired afternoon, but in a season of small, recorded tests. Start with one base and five tiles, and let the rest follow.
