The glass industry is pursuing two important pathways to reduce emissions. One is the use of more efficient raw materials, such as anhydrous borax as a boron source. The other is the adoption of cold-top electric furnaces as glassmakers continue their electrification journey.
However, these two sustainability trends do not always align perfectly. While anhydrous borax offers well-known melting and energy advantages, its use as the sole boron source in cold-top electric furnaces can contribute to temperature hot spots and "volcano" behavior on the batch blanket.
A collaboration between U.S. Borax and CelSian , “Optimizing Boron Sources and Hydroxides for Cold-Top Furnaces to Prevent Hot Spots and Volcano Effect” published in Glass Europe , explored exactly that question. The findings point to a more nuanced answer. Rather than eliminating crystal water entirely, the key may be retaining just enough crystal water to maintain stable operation in cold-top electric furnaces while preserving most of the benefits of anhydrous borax.
A practical finding
To better understand the phenomenon, our study evaluated different borate formulations in a laboratory-scale, cold-top electric furnace. The key finding was straightforward: As little as 20% borax pentahydrate was sufficient to significantly reduce the temperature surges observed when using 100% anhydrous borax. Similar benefits were also observed when crystal water was introduced through hydroxide-containing raw materials.
The results suggest that glassmakers may not need to choose between anhydrous borax and stable electric melting. Instead, a relatively small amount of crystal water can have a disproportionate impact on melting stability, while allowing the majority of the boron input to remain in anhydrous form.
Why crystal water matters
Infrared measurements showed that batches containing 100% anhydrous borax in a cold-top furnace experienced temperature spikes up to 150-200 °C higher than the alternative formulations shortly after batch addition.
The proposed explanation is surprisingly simple.
Crystal water released at lower temperatures appears to help create a more permeable batch structure. Rather than allowing gases to accumulate beneath a dense layer and escape suddenly, the early release of water vapor helps create pathways for gradual gas release and pressure relief. This reduces the likelihood of hot spots and volcano-type behavior.
Perhaps more importantly, the study suggests that the source of the crystal water may be less important than its presence. Whether supplied through hydrated borates or other hydroxide-containing raw materials, a similar stabilizing effect was observed.
A practical lesson for electrified glass melting
The broader lesson is not about a specific percentage. It is about understanding how a relatively small amount of crystal water can improve batch behavior and stabilize cold-top electric furnaces while allowing most of the boron source to remain anhydrous.
The 20% borax pentahydrate addition should not be viewed as a fixed requirement. It was simply the lowest level evaluated in this study that effectively mitigated temperature surges.
The optimal level will vary by glass composition, batch recipe, cullet content, pull rate, and contribution from other raw materials. Some glassmakers may achieve similar results with even lower additions.
Read the full paper: "Optimizing Boron Sources and Hydroxides for Cold-Top Furnaces to Prevent Hot Spots and Volcano Effect" in Glass Europe.
Please reach out to our technical team if you have any questions or would like to discuss the research further.
