Testing Hard and Soft Enamels on Pre-Coated Steel Panels
With a bit of High Firing as well
The viscosity of different enamels fired at the same temperature and for the same time varies. Those which flow easily at lower temperatures are ‘soft’ and those with a higher flowing point are ‘hard’. (Think runny honey v. stiff jam.)
It is important to know about this in order to prevent, or encourage, a lower layer of softer enamels from breaking through an upper layer of harder enamel to give a spotted effect. Soft enamels on top of hard give the expected even result, but the opposite can be exciting or frustrating depending on the desired outcome. It is of particular importance when using opaque enamels or opaque and transparent together. Transparent on transparent does not normally show breakthrough.
Many enamellers use ‘high firing’ on copper as a technique. This is carried out at higher than normal temperatures, around 930°C, and encourages breakthrough, unexpected transparencies and colour changes.
Recommended top firing temperatures depend on the individual manufacturer from whom lists can be obtained. For example Soyer hard enamels can be fired at 840° to 900°C, their medium ones at 800° to 840°C and their soft ones at 750° to 800°C. Schauer generally suggest lower temperatures.