The liquid glass was just a syrupy solution of sodium silicate. It rinsed off readily. If I remember right it was called water glass.

PS from my dictionary, water glass, definition 4:

sodium silicate or, sometimes, potassium silicate, occurring as a stony powder, usually dissolved in water to form a colorless, syrupy liquid used as an adhesive, as a protective or waterproofing coat, as a preservative for eggs, etc.