This 1 gallon heavy crock was fired to cone 6 (at 108F/hr during the final 200 degrees) and soaked 20 minutes (in a electric kiln). The bare clay base should be the color of the top test bar (which has gone to cone 6). Yet, it is the color of the bottom bar (which has gone to cone 4)! That means the base only made it to cone 4. The vertical walls are the right color (so they made cone 6). It may seem that this problem could be solved by simply firing with a longer hold at cone 6. But electric kilns heat by radiation, that base will never reach the same temperature as the sidewalls!
The term vitrified refers to the fired state of a piece of porcelain or stoneware. Vitrified ware has been fired high enough to make it very strong, hard and dense.
The process of holding a kiln at the final temperature (or at other temperatures) to enable the heat to penetrate the ware or to effect or complete a glaze or body reaction
Designing a good kiln firing schedule for your ware is a very important, and often overlooked factor for obtained successful firings.
Electric Hobby Kilns: What You Need to Know
Electric hobby kilns are certainly not up to the quality and capability of small industrial electric kilns, but if you are aware of the limitations and take precautions they are workable.