Shino is a high-feldspar glaze family known for a thick, milky white surface with orange and grey markings, and for carbon trapping: soot forced into the glaze early in the firing and sealed there as it melts. It is one of the least predictable glazes in common use and that is precisely why potters keep firing it.
What carbon trapping is
If the kiln is reduced early, while the glaze is still porous, carbon from the incomplete combustion is drawn into the glaze layer. As the glaze melts it seals that carbon in, giving grey to almost black markings under a white surface. The timing is what controls it, which is why the same glaze in the same kiln can vary from pot to pot in one firing.
Why shinos crawl and pinhole
They are applied thickly and carry a lot of feldspar and often soda ash, so they shrink considerably as they dry on the pot. That shrinkage can pull the raw glaze away from the surface, which becomes a crawl in the firing. Pinholes come from gas escaping late. Both are characteristic rather than exceptional, and heavy shino users learn to apply thinly where they do not want them.
The colour comes from the body as much as the glaze
Iron in the clay migrates into a shino during firing and produces the orange and rust markings the glaze is loved for. On a white body a shino reads much plainer. That is a rare case where the answer to a glaze problem is to change the clay: an iron-bearing body will do more for a shino than any adjustment to the recipe.
Whether to start here
Not as a first glaze. Shinos need reduction to do the interesting things, are unpredictable by nature, and are applied thickly enough to run if misjudged. As a second or third glaze in a studio that fires reduction regularly, they are among the most rewarding surfaces available.
Questions people ask about shino glaze
What is carbon trapping?
Soot drawn into a porous glaze during early reduction and sealed in as the glaze melts, giving grey to black markings under the surface.
Why does my shino crawl?
Shinos are applied thickly and shrink as they dry, which can pull them from the surface. Thinner application in problem areas is the usual fix.
Can shino be fired in an electric kiln?
It will melt, and without reduction it will not carbon trap or develop the same markings. The character comes from the atmosphere.