Molten Aura Labs Introduces SANDCRAFTED® Borosilicate Colors
Our unique process begins with crystalline quartz silica. That silica gets combined with high-purity chemicals, then melted into glass at temperatures exceeding 3000 degrees Fahrenheit. Samples of each formula are tested at The Orton Materials Testing and Research Center for exact strain point, annealing point, and CTE (Coefficient of Thermal Expansion).
Every element we use in the glass affects it’s working characteristics in some way. Having complete control over the composition allows us to minimize undesirable traits while maximizing color saturation and usability. No color is ever going to work exactly like clear. However, we go to great lengths to ensure that the balance of CTE and viscosity ensures compatibility with the NIST Borosilicate standard (3.3 x 10-60).
Why make SANDCRAFTED® colors?
Simply put, we wanted stronger colors without sacrificing compatibility. To us, the industry standard process of buying clear glass, grinding it into powder, and adding small amounts of colorants seems outdated and inflexible. Clear borosilicate is essentially 81% Silica, 13% Boron, 4% Alkali, 2% Alumina. As soon as you add anything to the clear cullet to colorize it, you alter the ratio, changing its workability. With few exceptions, you cannot develop strongly colored, perfectly compatible glass using this method. And now we are seeing that even those few exceptions are being “watered down” to minimize their own inherent issues such as boiling, excessive air content, or color burnout.
The obvious question is, “why not make colored borosilicate from scratch?”. It didn’t take us long to figure why it wasn’t already being done. It’s hard. There’s no easy way to melt 81% silica and produce pristine, strongly colored, flame-workable glass that clocks in at exactly 33CTE.
But our desire to push the boundaries of glass and technology to create deep, vibrant colors for the borosilicate palette, drove us to persist. If you are familiar with painting and the process of mixing colors, then you know that a color can never get any more saturated than it is “straight from the tube”, so to speak. As soon as you mix a color with any other color, it loses intensity. A painter has the luxury of starting with extremely saturated colors, allowing for the maximum range of hue, saturation, and value in the final work. In a similar way, we want to give glass artists a deeper toolset to choose from.
Our vision is to propel a new generation of borosilicate artwork forward with the richness and optical clarity that has been a staple in soft glass for centuries. We see SANDCRAFTED® glass as the logical next frontier for discerning borosilicate artists.
Moonstone has been tested by Orton Materials Testing and Research Center for exact strain point, annealing point, and CTE (Coefficient of Thermal Expansion). Moonstone is 33CTE (3.3 × 10-6 (1-300°C)) and is fully compatible with clear borosilicate. It has an annealing point of 1150°F and a strain point of 1035°F. Look for this data on all of our new colors moving forward in addition to any reformulations of existing colors.
This is a photo of a simple paddle under a polariscope. Left image shows the strain before annealing, and the right image shows all strain being relieved after 15 minutes at the upper end of the annealing range.
We know that CTE doesn’t tell the full story about compatibility, but it is a good starting point. The viscosity of the glass, particularly within it’s cooling temperature range, is a huge factor as well. This is where a polariscope becomes an essential tool for the modern glassmaker (and glassblower!). You can use a small piece of polarized film and use your cellphone’s white screen as the light source (most phone displays emit polarized light). This will work for you in a pinch if you don’t have access to a laboratory grade polariscope.