Zinc Sulphide Phosphor: Precipitated Sulphide Heated to Redness with a Flux (Thorpe 1913)

Precipitated zinc sulphide does not glow. Heated to redness together with an alkali chloride or the sulphide of another metal, it turns into the phosphorescent sulphide used for fluorescent screens. Source: Thorpe, Dictionary of Applied Chemistry vol. 5 (1913), Zinc. Unknown: which chloride or sulphide, how much, and for how long. Thorpe names only the class, so the additive is linked to an unknown head. Crucible and furnace are ours. Picture drawn by Youblob.