soiling vs spotting

soiling and spotting both are nouns.

Word	Noun	Adjective	Verb	Adverb
soiling	Yes	No	No	No
spotting	Yes	No	No	No

As nouns, spotting is a hyponym of soiling; that is, spotting is a word with a more specific, narrower meaning than soiling:

Other hyponyms of soiling include maculation, staining, contamination, pollution.

soiling (noun)	spotting (noun)
the act of soiling something	the act of detecting something; catching sight of something
	the act of spotting or staining something