Which glass releases alkali as described in the material?

• A. Flint glass (soda-lime glass)
• B. Soft glass (boron-free)
• C. High silica glass
• D. Low actinic glass

Answer: (A)

Alkali release from glass depends on its composition, specifically the presence of alkali oxides that can leach out. Flint glass, or soda-lime glass, contains significant sodium oxide (and other alkalis) used as a flux to lower its melting temperature. When this glass comes into contact with fluids, these alkali ions readily dissolve and migrate into the surrounding medium, so it is the one that releases alkali. High silica glass is dominated by SiO2 with little alkali, making it much more resistant to leaching. Soft glass described as boron-free may lack boron but can still contain alkalis, and low actinic glass is chosen for optical filtering rather than chemical durability. The material with the inherent alkali content that leads to release is the soda-lime (flint) glass.