Viscosity - Flow Cup

The viscosity, or thickness, of a dipping glaze is very important. If the glaze is too thin or too thick, the glaze layer on the clay body will also be too thin or too thick. This can affect the colour or cause the glaze to run during firing.

Viscosity is not a fixed value. It changes under the influence of environmental factors such as the temperature in your studio. A glaze may be fluid and runny one day, then thick and viscous again a few weeks later. Always check the viscosity before dipping or pouring, and only do it after you measured and adjusted specific gravity.

Stir the glaze thoroughly. It should be perfectly mixed. Then fill a flow cup with a 4 mm opening completely with glaze. Lift the cup in one smooth motion so the glaze can flow through the opening and start a stopwatch at exactly that moment. Stop the timer as soon as the flow is interrupted for the first time. Repeat this several times and calculate the average of the measured times in seconds.

Compare your result with the target value indicated on the SOGO glaze label. Is your flow time longer? Then the glaze is too thick and will need to be thinned, either by adding water or by deflocculating it with Dolapix. Is the flow time shorter? Then the glaze is too fluid and needs to be thickened, or flocculated, with Epsom salts.