|Monthly Tech-Tip |
Both are low fire transparents. In a melt fluidity test they flow in a similar fashion. But here, where a 10 gram ball has melted down onto the tile, differences in surface tension are clearly evident by the angle at which the edge of the glaze meets the tile.
Low-fire glazes must be able to pass the bubbles they and the underlying bodies generate (or clouds of micro-bubbles will turn them white). This cone 04 flow tester makes it evident that 3825B has a higher melt fluidity (A has not even dripped onto the tile). And its higher surface tension is demonstrated by how the flow meets the runway at a perpendicular angle (it is also full of entrained micro-bubbles). Notice that A, by contrast, meanders down the runway, a broad, flat and relatively clear river. Low-fire glazes must pass many more bubbles than their high-temperature counterparts, the low surface tension of A aids that. A is Amaco LG-10. B is Crysanthos SG213 (Spectrum 700 behaves similarly, although flowing less). These two represent very different chemistry approaches to making a clear glaze. Which is better? Both have advantages and disadvantages.
In ceramics, glazes melt to produce a liquid glass. That glass exhibits surface tension and it is important to understand the consequences of that.