The difference is a slow-cool firing. Both mugs are Plainsman M340 and have a black engobe inside and partway down on the outside. Both were dip-glazed with the GA6-B amber transparent and fired to cone 6. The one on the right was fired using the PLC6DS drop-and-hold schedule. That eliminated any blisters, but some pinholes remained. The one on the left was fired using the C6DHSC slow-cool schedule. That differs in one way: It cools at 150F/hr from 2100F to 1400F (as opposed to a free-fall). It is amazing how much this improves the brilliance and surface quality (not fully indicated by this photo, the mug on the left is much better).
Firing Schedules |
Plainsman Cone 6 Slow Cool (Reactive glazes)
|
---|---|
Firing Schedules |
Cone 6 Drop-and-Soak Firing Schedule
|
Recipes |
GA6-B - Alberta Slip Cone 6 Amber Base 2
An amber-colored glaze that produces a clean, micro-bubble-free transparent glass. Works well on brown and red burning stonewares. |
Troubles |
Glaze Pinholes, Pitting
Analyze the causes of ceramic glaze pinholing and pitting so your fix is dealing with the real issues, not a symptom. |
Glossary |
Pinholing
Pinholing is a common surface defect that occurs with ceramic glazes. The problem emerges from the kiln and can occur erratically in production. |