Liquid sodium silicate (water glass) is classified under 283919, which covers sodium silicates other than sodium metasilicate. Sodium metasilicate—a distinct crystalline compound with a specific Si:Na ratio—falls under 283911. The ratio of SiO₂ to Na₂O and the physical form (solution vs. anhydrous solid) are key classification indicators.

Potassium silicates, lithium silicates, and other non-sodium alkali metal silicates are captured under the residual subheading 283990. Importers should confirm the specific 10-digit HTS line with a customs broker, as the precise alkali metal and form can affect duty treatment.