All glass, with the exception of fuzed quartz, has sodium and silica as a significant part of their formulation. The sodium content ranges from under 1% for E-Glass, to 4% for type 33 borosilicate, and up to 15% for some container and plate glasses. The net effect of the sodium content, coupled with the low but measurable solubility of glass, causes elevated pH in 10% solids solution with water. The pH ranges from 9-11, and will drift higher over time as additional glass solubilizes. This phenomena can cause rheology problems in water based systems such as coatings and glazes.
Neutral pH glass is a proprietary treatment developed by Vitro Minerals to take any composition of glass of any particle size and adjust pH to levels of 5-8, with those pH values staying relatively stable in water based systems for indefinite periods of time.