The phrase "a scum of" is correct and usable in written English.
It is typically used to describe a contemptible or despicable person or group, often in a derogatory context.
Example: "He was considered a scum of society for his unethical actions."
Alternatives: "a lowlife of" or "the dregs of".
A trike lay tipped over in the rutted grass, and a plastic pool of water held a scum of leaves.
They're an unavoidable by-product of power, a scum of pure ego that forms on the surface of society and imitates the appearance of leadership.
In the open gutters a tide of the same unearthly blue slowly pushes through a scum of animal hair, bits of skin and rubbish.
In the corner of the harbour, away from the fancier boat-palaces, are the smaller vessels bobbing up and down in a scum of Evian bottles and patisserie paper, the wrappings of croissants, long-consumed, swirling around in an endless eddy.
That meant four prisoners per square metre: night and day, the prisoners had to stand, or to sit between the legs of those who stood, and even in the dry season a scum of dampness, urine, and bits of dropped food covered the floor.
And they are suggesting that a scum of iron-rich mineral is now frozen around the rest of the core, which is still liquid.
Hands down the most noxious character in "Tropic Thunder" is Les Grossman, the producer of the movie-within-a-movie, who's played by an almost unrecognizable Tom Cruise under a thick scum of makeup and latex.
There, Georgie sees him in bright light after mistakenly climbing into bed with him: "The whiteness of his face was shadowed by a gray scum of unshaven whiskers.
They ordered beers, and when the beers arrived the big man in the hat drank deeply and then leaned toward Sid, a pale scum of suds covering his upper lip.
Though waterbirds, including moorhens and gulls, live on the margins, and a thin scum of litter is visible at the shore, the reservoir is not intended as a home to wildlife, and any fish living here are accidental visitors.
That means they have greater potential to be exposed". As large marine mammals, they also broke through the surface of water coated with a thick scum of oil and they inhaled the fumes from the giant fires used to burn off the oil.
