This article aims to explain why a pottery glaze, when melted to a certain temperature, exhibits variegations
We suggest that specific gravity (SG) of the new overlay pottery glaze falls within a desired range, maintaining it within that range ensures proper consistency and application of the glaze
Refer to recently posted Part 1 reel for detailed instructions on how to measure specific gravity and how to perform dip tests on test tiles
When a non-variegating glaze is layered over another non-variegating glaze the overlay glaze melts into the underlying glaze
For instance, if a matte glaze is applied as an overlay glaze over a gloss glaze, the final outcome will be predominantly matte. On the other hand, if a gloss glaze is applied as an overlay glaze over a matte glaze, the final result will be mainly glossy. In both cases, the chemistries of the two glazes do not mix or create a new third glaze. Instead, the overlay glaze retains its own characteristics
However, when certain compounds, such as titanium dioxide, are included in the overlay glaze, a phenomenon called phase separation can occur.
What is Phase separation?
Phase separation refers to the separation of different components of the overlay glaze, resulting in the formation of two separate glazes, each with its own distinct chemistry. This separation leads to variegation in the final appearance of the glaze
This phenomenon is also known as variegation, these variegations result in a visually interesting surface. Variegations range from subtle breakouts to a more pronounce patterns. Adjusting concentrations of those compounds will influence the extent of variegation
It is worth, noting that achieving consistent, predictable variegations can be challenging the outcome may vary, depending on factors, such as final firing temperature, cooling cycle, and the specific compounds used and therefore experimentation is necessary
Happy potting to you! 😀
