I gave one glance at the black scum on top of the water, and decided to go dirty for the day.

我瞥了一眼水面上漾着的那层发黑的泡沫，就打定主意这一天就脏着脸过了。

youdao

Floating on top of the greenish pool - a mixture of 70% water from the Dead Sea and 30% water from the Red Sea - is a white scum of algae.

绿色的池面(由70%的死海水和30%的红海水混合而成)上，漂浮着一团白色的藻类。

youdao

The circular movement of the cooking foods also meant that scum or skin formed neatly in the center, making it easier to skim the residue off the top.

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