There's an amazing amount of information in this thread. Thanks so much.
Further to the rate of firing/slow cooling concept, I have been surprised at the amount of glaze alteration that can occur on refiring Cone 6 glaze fired ware to lower temperatures. For example to mature china paint or attach decals. I have seen noticeable permanent visual change in glazes when refired to as low as 1450F which must be below glaze softening temperature. This has been most noticeable in titania containing glazes. (Thank you Joseph for alerting me to that.)
To guide exploration of glaze manipulation at such very low temperatures I'm interested in further information and concepts regarding
Lowest temperatures at which permanent glaze appearance alterations can occur?
Glaze ingredients and combinations which may react at these lower temperatures?