in solvent extraction
A deposit or emulsion
at the interface
between two partially settled phases.
The phenomenon of crud formation arises from many causes and this definition does
not imply any single one.
Other terms -- some unprintable -- have been used but crud is the generally accepted
PAC, 1993, 65, 2373
(Nomenclature for liquid-liquid distribution (solvent extraction) (IUPAC Recommendations
on page 2387