The chemistry of a Shino glaze and my path to a peach skin finish
For years I treated Shino glazes like a secret language whispered between kiln doors. The first time I opened a lid in my Barcelona studio and saw a soft, blushing surface staring back at me, I knew I had to learn the vocabulary. The peach skin finish I now chase across my decorative plates is the result of endless testing, a few spectacular failures, and a slow education in the mineral heart of clay.
Australian potters often ask me how I landed on this particular surface, especially after showing work at exhibitions in Sydney and Brisbane. The short answer is patience and a willingness to read chemistry like a recipe. The longer answer is what follows, from the volcanic ash traditions of Mino province to the precise ratios of feldspar and soda ash that I now rely on in my workshop just outside the Gothic Quarter.
The Mino tradition and why Shino still matters
Shino glazes were born in sixteenth-century Japan, where potters working in the Mino valley layered wood ash and feldspar-rich rock over a coarse stoneware body. The result was a tactile, often orange to grey surface that seemed to glow from within. When I first read about the carbon trapping that happens during early reduction firing, the technique felt like alchemy. Today, working with contemporary Shino variations means blending soda ash, nepheline syenite, and ball clay in proportions that would have made those original Mino masters raise an eyebrow.
What draws me back to Shino is the same thing that drew the Japanese tea masters: the glaze is alive during firing, shifting and pooling wherever the flame licks the pot. A teabowl can emerge looking like wet river stone on one side and dry desert earth on the other. That duality is something I try to honour in my own abstract pieces, where the peach skin finish needs to feel both ancient and immediate. The way a Shino breaks over a curved form has shaped my recent sculptural work, and I often return to my notes on wave symbolism when a piece feels too static.
The mineral cocktail: feldspar, soda, and a touch of iron
A traditional Shino is roughly seventy percent feldspar, twenty percent soda ash, and ten percent ball clay, though every studio in the world seems to have its own slight deviation. The feldspar acts as the flux, lowering the melting point and creating that glassy network across the surface. Soda ash, which is essentially sodium carbonate, helps the glaze climb up the pot rather than sliding off. The ball clay keeps everything suspended in the bucket, preventing the heavier minerals from settling.
The peach skin quality comes from a very specific addition: a small percentage of red iron oxide, usually around two to four percent. Iron in a reduction atmosphere turns into ferrous oxide, which migrates to the surface and forms a thin, crystalline skin. When the cooling is slow enough, that skin breaks into a texture that reminds me of the inside of a ripe peach. A studio assistant in Melbourne who had trained in Kyoto taught me part of this. The piece on negative space in typography discussed how empty surface area carries meaning, which clarified why a matte Shino sometimes says more than a glossy celadon.
Firing schedules and the carbon trap
The real magic of a Shino happens before the glaze even melts. Between 800 and 950 degrees Celsius, the soda ash begins to release carbon dioxide. If the kiln is starved of oxygen during this window, the carbon gets trapped in the forming glass and creates those signature grey, smoky patterns. This is what potters call a carbon trap, and it is the soul of the glaze.
In my gas kiln, I hold the temperature just below 900 for thirty minutes with the damper nearly closed, then crack it to let the atmosphere go neutral and the iron bloom. For electric kiln users in Australia, the trick is to add a piece of newspaper or sawdust to a closed saggar at the right moment, or, as Brisbane potters I know do, a teaspoon of crude sugar to the glaze bucket. Each method is a small rebellion against modern uniformity, a way of coaxing a wild, living surface out of a process that manufacturing would prefer to tame.
Troubleshooting the peach skin finish
The most common frustration with a Shino is crawling, where the glaze pulls away from the clay body during firing and leaves bald patches. This usually happens when the clay is too dusty or the glaze is applied too thick. I now wipe every pot with a damp sponge right before glazing, and I aim for a coat no thicker than a sheet of paper. Another problem is pinholing, which occurs when gases escape from the clay body too late in the firing. Bisquing to cone 06 and confirming the body is fully vitrified before the final glaze fire solves most of it.
The goldilocks zone for the peach skin finish is frustratingly narrow. Too much reduction and the surface goes matte and dry. Too little and the iron never gets a chance to migrate. I keep a notebook next to every kiln load, logging gas pressure, damper position, and the exact time of each adjustment. It is tedious work, but the only way to repeat a result is to record the conditions that produced it. When I shared some of these notes with a group in Adelaide last winter, one of the participants asked if the science was taking the romance out of the process. The honest answer is that it has deepened my respect for the clay.
Application techniques and practical notes for Australian ceramicists
How a Shino is applied matters as much as how it is mixed. Brushing leaves streaks of colour, which I love on sculptural pieces but avoid on tableware. Dipping gives the most even coat, but the dwell time must be consistent or the glaze thins near the rim. For the peach skin finish, I spray the first two layers and then dip the pot for a final ten seconds, building enough thickness for the iron to migrate without drowning the carbon trap. Readers interested in similar surface work on a smaller scale can see how I approached a recent toothbrush holder design.
Working with raw minerals in Australia has practical realities. The Department of Agriculture, Fisheries and Forestry requires permits for some specialty imports, and soda ash occasionally faces biosecurity scrutiny. Local suppliers in Sydney and Perth keep stock of nepheline syenite and ball clay, saving paperwork and waiting time.
A few recommendations for anyone starting out:
- Always bisque to cone 06 and confirm the clay body is fully vitrified before the final Shino fire.
- Keep a dedicated bucket and fine-mesh strainer for Shino glazes, and label every mix with the date and percentages.
- Photograph every test tile under consistent natural light so you can track how the peach skin finish develops over time.
- Join a local firing group or open studio night; the collective knowledge of potters in Brisbane and Melbourne is worth more than any textbook.
- Order your feldspar and soda ash from Australian suppliers where possible to avoid biosecurity paperwork on imported minerals.
If you would like to see the peach skin finish in person, my workshops in Barcelona and select dates in Australia offer hands-on time with these glazes. Mailing list subscribers receive firing schedules, recipes, and first notice of new pieces. For Australian readers looking for creative collaborators who understand experimental ceramic practice, the team at Gestalt Projects have long championed this kind of work. You can also follow along on Instagram where I share the messy, mid-process moments that never make it into a polished portfolio shot.