|Monthly Tech-Tip |
These two glazes have the same chemistry but different recipes. The F gets its boron from Ulexite, and Ulexite has a high LOI (it generates gases during firing, notice that these gases have affected the downward flow during melting). The frit-based version on the right flows cleanly and contains almost no bubbles. At high and medium temperatures potters seldom have bubble issues with glazes. This is not because they do not occur, it is because the appearance of typical glaze types are not affected by bubbles (and infact are often enhanced by them). But at low temperatures potters usually want to achieve good clarity in transparents and brilliance in a colors, so they find themselves in the same territory as the ceramic industry. An important way to do this is by using more frits (and the right firing schedules).
Loss on Ignition is a number that appears on the data sheets of ceramic materials. It refers to the amount of weight the material loses as it decomposes to release water vapor and various gases during firing.
Frits are used in ceramic glazes for a wide range of reasons. They are man-made glass powders of controlled chemistry with many advantages over raw materials.
Suspended micro-bubbles in ceramic glazes affect their transparency and depth. Sometimes they add to to aesthetics. Often not. What causes them and what to do to remove them.
Glaze Melt Flow - Runway Test
A method of comparing the melt fluidity of two ceramic materials or glazes by racing them down an inclined runway.