Blowing Colors and Kilncast Compatibility

edit:  This post was originally written back in 2014, long before the environmental issues of Bullseye Glass and Uroboros Glass arose in the media.  Readers may find this post more relevant in light of current events.

A variety of Reichenbach and Gaffer colors (rods) were tested for compatibility and color durability with glass from my batch formulation in kilncast glass slabs.

Generally, most colors are compatible.  In particular, colors with lead bases are quite compatible.  Typically, the opaque reds, oranges, yellows, and some greens show significant incompatibility.  Test samples with compatibility issues readily develop fissures at the interface between glass and color, sometimes quickly and sometimes over a period of a couple of weeks.  A few colors exhibit “crazing” at the interface, but did not develop fissures of a more structural nature.  Some colors exhibit greater incompatibility with increasing thickness.  A superficial study color variation (from rod to rod) did not indicate a high degree of variation, however I plan to continue to spot check new rods of “compatible” colors until I get a better feel for the variation between different rods of the same color.

Many of the colors show a high degree of durability, meaning that they do not tend to change significantly due to the high temperatures and long firing times of kilncasting applications.  Some color groups do show significant change however.  Opaques tend to become transparent, but retain their color.  Copper reds tend to burn out to a liver color.  Some gold-based reds, oranges, and yellows tend to become pink in tone.  Overall, the changes are usually interesting and typically reproducible; I’ve developed a sample set to reference for future casting projects.


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