This sample shows technical grade sodium sulfide of composition Na₂S·xH₂O, with x approximately equal to 3. Reagent grade sodium sulfide is the nonahydrate Na₂S·9H₂O, which is a white transparent crystalline solid. The technical grade compound is yellow. The yellow color may be due to imperfections in the crystal lattice. Solutions of this yellow compound are colorless, but become yellow on standing in contact with air.

The white color, seen at some scales is due to aerial oxidation. Sodium sulfide is quite air-sensitive. It is easily oxidized to a mixture of sodium sulfite, sodium thiosulfate and sodium sulfate. This mixture is the white powder on some scales.