|Monthly Tech-Tip |
The L4655 floating blue recipe is on the outside of the mug. It adds titanium to the GA6-A base. We wanted to reduce the thermal expansion to minimize the likelihood of crazing. So the obvious question was: Could we substitute the Ferro Frit 3134 for Frit 3195 in the base (effectively using GA6-B instead of GA6-A)? The calculation showed that the thermal expansion should drop from 7.6 to 7.2. Unfortunately, it did not work. The two tiles in the front show that (the one on the right adds 2% iron, we thought that might enhance the rutile blue effect). Why did this fail? Likely the raising of the Al2O3 makes the melt stiffer, that is preventing the freedom of movement needed to form the crystalline phases.
These two mugs have the Alberta Slip base cone 6 GA6-A glaze on the inside and GA6-C on the outside (it just adds rutile to GA6-A). The left one was cooled normally (kiln off at cone 6 after soak). For the mug on the right, the kiln was soaked for half an hour at 1800F on the way down to develop the rutile blue glaze on the outside. But during this period crystallization occurred on the inside also. This provides an insight into my this GA6-A base hosts floating blue effects but GA6-B does not: The amount of Al2O3 is much lower, that improves melt fluidity and acts as a catalyst for crystallization.