Notes on applying and
firing shino glazes.
Shino glazes are high in both alumina and silica and therefore tend to be rather stiff in the fire.
That is, they do not flow when molten like most other glazes. Therefore,
the glaze application is less forgiving. The mode of application,
including drips and flaws, will be evident when the pot emerges
from the kiln. Generally, shinos are applied by pouring or dipping.
Because shino glazes generally contain a soluble
component (usually sodium carbonate, "soda ash") , the
fired look of the glaze can be influenced by such factors as drying
time. Simple brushwork of wax resist over the freshly glazed pot
will show up as subtle marks on the fired glaze. Finger painting on the surface of the freshly applied, wet glaze can leave lovely, getural marks in the fired glaze. Sgraffito ("scratching through) techniques can be effective and remain as such in the stiff glaze surface. The soluble components of the glaze leave a dark sheen in the clay surface left exposed in this technique.
Shino glazes are extremely sensitive to atmospheric
conditions in the kiln during firing. Consequently, wood or gas
firings are necessary. Shinos fired in oxidation usually have a
rather uninteresting appearence. Reduction in a gas kiln should
commence early (generally by ^012) and maintained throughout the firing.
Heavy (smoky) reduction at the early stages favors the appearance
of carbon trapping. Some potters find an oxidizing soak at peak
temperature enhances fire coloring of this glaze. I provide a two-hour
oxidizing soak at the end of my shino firings. -BB