N yellow dye| any yellow color; mud| clay| dirt

soil, dirt, mire, mud loam, clay

Lutum was a glutinous mixture of linseed oil and clay used in the chemical industry to make a gas tight seal around the anodes of mercury cells for the production of Chlorine gas and Caustic Soda liquor (NaOH) from brine (NaCl), also Caustic Potash (KOH) from Potassium brine (KCl).
It was superceded in the latter half of the 20th Century by a rubberised sealant that was more flexible when set and less prone to cracking as it set, where lutum required regular oiling to maintain gas tightness.