Glaze firing ranges

[chrisclay]

can someone please clarify for me what exactly is implied when a glaze manufacturer states that a glaze has a range of from, say, 850 deg C to 1050 deg C...what is the precise (if such a thing exists in ceramics) significance of the 850 deg C figure, and of the 1050 deg C figure ?

[lockettpots]

It shows the range of temperatures at which acceptable results could be obtained.

Below the lower temperature (underfired) the glaze would not properly melt often giving rise to a dry, powdery looking surface.

Above the upper temperature (overfired) the glaze would become too fluid and could well run off the pottery on to your kiln shelves or other pieces.

Of course 'acceptable results' are very subjective and one potter may well prefer to fire near the lower temperature while another may prefer to fire the same glaze towards the higher temperature.

As you have realized pottery and particularly glazing and firing is not an exact science. More of an art;).

When using a new glaze potters will nearly always do some test firings at different temperatures and then choose from the results.

John

[chrisclay]

thanks, John, for clarifying that...i'd guessed that that was the case but i was not sure because it seemed such a wide range from low to high end of possible acceptable results

chris