From Brush to Kiln: The Complete Process Behind Pottery Painting Explained
You've painted your mug. You've handed it over to the studio team. And then.. nothing, for two to four weeks, until an email arrives telling you it's ready to collect.
What actually happens in between?
Most people who try pottery painting for the first time have no idea what the kiln process involves, why the colours look so different after firing, or what the difference is between glaze, bisqueware and slip. This post covers all of it, the full journey from raw clay to finished ceramic, explained properly. Not because you need a degree in ceramics to enjoy a session at pHresh, but because understanding the process makes the whole experience more satisfying. And honestly, the science of what happens inside a kiln is genuinely fascinating.
🏺 It starts long before you pick up a brush. What is bisqueware?
When you arrive at pHresh Pottery and browse the selection of pieces to paint, everything on the shelves is what's known as bisqueware, ceramic pieces that have already been through their first firing in a kiln, but haven't yet been glazed or decorated.
This first firing is called the bisque fire (sometimes spelled biscuit fire), and it typically takes place at around 900–1000°C. At this stage, the clay has been transformed from its raw, fragile state into something hard and porous, solid enough to handle and paint, but still absorbent enough to take on glaze paints properly.
The porosity is important. Raw bisqueware drinks up glaze paint in a way that fired, glazed ceramic never would. That's what makes painting on it feel slightly different to painting on paper or canvas, the surface pulls the paint in almost immediately, which is why your brushstrokes feel a little different and why building up layers of colour works so well.
The pieces you choose at pHresh have been through this bisque fire before they ever reach the studio shelves. All you're doing is the decorating stage, which is, admittedly, the most enjoyable part.
🎨 The paints you're using aren't really paints
This is the thing that surprises most people: the coloured liquids you're painting with aren't paint in the conventional sense. They're underglazes or glaze stains, essentially, metalite oxides and minerals suspended in a liquid medium.
At room temperature they look like poster paint. They behave a bit like watercolour. And they look nothing like what they'll become after firing.
What's actually in a glaze paint?
Glaze paints are made up of three basic components:
Colourants: metal oxides that produce specific colours when heated. Cobalt produces blue. Iron oxide produces browns and reds. Copper produces greens and sometimes turquoise. Manganese produces purples and browns. Chrome produces greens. These aren't dyes — they're minerals that literally change structure at high temperature.
A flux: a material that lowers the melting point of the glaze so it fuses to the ceramic at kiln temperature rather than requiring temperatures that would destroy the piece.
A carrier: the liquid base that keeps everything suspended and makes it paintable.
When you apply these colours to your bisqueware piece, you're essentially laying down a coating of minerals that will, under heat, melt, fuse together, and vitrify into a glassy surface. The colour you see on the brush is almost irrelevant, what matters is what those minerals do at 1000°C.
This is why the colours look so different after firing. You're not just "baking in" the colours you painted. You're creating an entirely new surface through a chemical and physical transformation.
🖌️ Why technique matters more than artistic talent
Because of the way underglazes behave, the techniques that produce great results in pottery painting are quite different from conventional painting.
Layering Unlike watercolour or acrylic, glaze paints reward multiple thin coats more than a single thick application. Two or three thin layers of the same colour will produce a more vibrant, even result than one thick coat, which can crack or bubble during firing. At pHresh, the team will often suggest going back over areas you've already painted, this isn't inefficiency, it's the right technique.
Colour mixing You can mix underglazes directly on your piece to create new colours, just as you would with conventional paint. However, be aware that mixed colours don't always fire in the way you'd expect, some combinations interact in surprising ways at high temperature. Blues and greens tend to be the most predictable. Reds and pinks can shift. If you're attempting a specific mixed colour for the first time, ask the pHresh team, they've seen most combinations come out of the kiln and can tell you roughly what to expect.
Contrast and detail Dark underglazes on light bisqueware produce sharp, clear detail. Light colours on darker backgrounds are harder to achieve and often require more layers. If you want fine detail work, lettering, outlines, intricate patterns, a liner brush and a steady hand are your best tools. Stencils are also available at pHresh if you want crisp, repeatable shapes without freehand stress.
Leaving space One technique that beginners often overlook: leaving areas of the bisqueware unpainted, or painting them with a clear glaze, can produce beautiful results. Not everything needs to be covered. White space, or in this case, raw bisque space, is a legitimate design choice.
🔥 What happens in the kiln
This is where it gets genuinely interesting.
After your session, the pHresh team takes your painted piece through a two-stage finishing process before it goes into the kiln.
Stage 1: Clear glaze application Once your underglaze decoration is dry, a clear glaze is applied over the entire piece. This is typically done by dipping, spraying or brushing, depending on the shape of the piece. The clear glaze is what produces the glossy, smooth surface of a finished ceramic. Without it, the fired piece would be matte, slightly rough, and not food-safe. The clear glaze also amplifies and deepens the colours underneath, which is a large part of why the finished piece looks so different from how it looked when you left.
Stage 2: The glaze fire The piece then goes into the kiln for its second firing, the glaze fire. This happens at a higher temperature than the bisque fire, typically between 1000°C and 1220°C depending on the type of clay and glaze being used.
Inside the kiln, several things happen simultaneously:
The clear glaze melts and flows across the surface, encasing your decoration in a layer of glass
The underglaze colours fuse permanently into the ceramic body
The metal oxides in your colours undergo chemical reactions that produce their final hue, this is the moment cobalt becomes brilliant blue, copper becomes deep green, iron becomes warm amber
The entire piece vitrifies, meaning the clay body itself densifies and hardens to its final, permanent state
The kiln is then cooled slowly, too fast and the thermal shock can crack or shatter the piece. This cooling process alone can take many hours.
What comes out of the kiln is fundamentally different from what went in. The surface is glassy and smooth. The colours are deeper and more saturated. The piece is now durable, food-safe, dishwasher-safe, and permanent. What was a chalky, painted bisque piece is now a finished ceramic object that will last, with reasonable care, essentially forever.
🌈 Why do my colours look so different after firing?
This is the question we get asked most often, and it deserves a proper answer.
The short version: because you weren't painting with colour. You were painting with minerals that become colour under heat.
The longer version:
Blues and purples: cobalt-based colours tend to intensify dramatically after firing. A pale, slightly grey-blue underglaze often fires to a deep, rich cobalt. If you painted something that looked a bit washed out and it comes back vivid and saturated, this is why.
Greens: copper and chrome-based greens also tend to intensify and sometimes shift slightly in hue. Copper glazes in particular can produce beautiful variations, from pale celadon to deep teal depending on the firing atmosphere inside the kiln.
Reds and pinks: these are the most unpredictable. Iron-based reds can shift toward orange or brown. Some pink underglazes fire beautifully; others can become more muted. If a specific red or pink result matters to you, it's worth asking the pHresh team for guidance before you paint.
Browns and blacks: manganese and iron-based colours tend to be relatively stable and predictable. Browns often deepen; blacks stay strong.
Yellows: can sometimes appear slightly different after firing, often becoming warmer and more golden.
Whites and creams: relatively stable, though the clear glaze over the top adds a slight warmth that can make stark white appear more ivory.
The practical takeaway: if your piece looks a little flat or dull when you leave the studio, don't worry. The kiln is doing something remarkable to it. Trust the process.
⏱️ Why does it take two to four weeks?
Understandably, a lot of people want their piece back immediately. Two to four weeks can feel like a long time when you've just painted something you're excited about.
The timeline exists for a few reasons:
Drying time: after painting, pieces need to dry completely before the clear glaze is applied. Rushing this stage can cause the glaze to apply unevenly or the piece to crack during firing.
Kiln batching: running a kiln for a single piece is neither practical nor energy-efficient. Studios typically batch pieces together to fire a full kiln load, which means waiting until enough pieces are ready to justify a firing cycle.
Firing and cooling: a full glaze fire, including the slow cooling phase, can take anywhere from 12 to 24 hours. This isn't something that can be rushed without risking the pieces inside.
Quality checking: after firing, pieces are checked before being made available for collection.
The wait is worth it. Almost everyone who collects their piece is surprised by how much better it looks than they expected.
🧪 A quick glossary
For anyone who wants the terminology straight:
Bisqueware: ceramic that has been fired once but not yet glazed. The stage at which you paint at pHresh.
Underglaze: the coloured paint used to decorate bisqueware. Made from metal oxides, flux and a liquid carrier.
Glaze: a glassy coating applied over underglaze decoration before the final firing. Produces the smooth, glossy surface of finished ceramics.
Bisque fire: the first kiln firing that transforms raw clay into bisqueware. Typically 900–1000°C.
Glaze fire: the second kiln firing that melts the glaze and fuses it permanently to the ceramic. Typically 1000–1220°C.
Vitrification : the process by which clay densifies and hardens during high-temperature firing, becoming non-porous and permanent.
Flux: a material in the glaze that lowers its melting point, allowing it to fuse to the ceramic at achievable kiln temperatures.
Metal oxides: the minerals that produce colour in glaze paints. Cobalt for blue, copper for green, iron for red/brown, manganese for purple/brown.
🏛️ A brief note on why any of this matters
Pottery is one of the oldest human technologies. The earliest known fired ceramics date back over 20,000 years. The basic chemistry happening in a kiln today, metal oxides transforming under heat, clay vitrifying, glaze melting into glass, is fundamentally the same process that was used in ancient China, ancient Greece, and medieval Europe to produce the ceramics that now sit in museums.
When you paint a mug at pHresh on a Tuesday evening and hand it over to be fired, you're participating in a process that connects directly to the very beginning of human craft. The technology has been refined over millennia, but the essential act, shaping and decorating clay, then using fire to make it permanent, hasn't changed.
That's a lot to carry in a mug. But it's worth knowing.
📍 Come and try it yourself
Understanding the process is one thing. Experiencing it is better.
pHresh Pottery is on Lavender Hill in Battersea, SW11 — ten minutes from Clapham Junction on foot. Midweek evening slots are available Tuesday through Thursday. BYO alcohol is welcome. Over 50 ceramics to choose from.
Book your slot at letsbookfor.com/phresh-pottery
Or find out more at phresh.london/homestudio
pHresh Pottery · 103F Lavender Hill · Battersea · SW11 5QL
