Using ''de / d' '' instead of 'des' in front of adjectives preceding nouns (partitive article)

Look at these sentences:

Note that when the adjective is placed BEFORE a plural noun, the partitive article des (some) becomes de (or d' in front of a vowel or mute h). 

ATTENTION:
This rule doesn't apply when des is the contraction of "de + les" (= of/from/to the) :

BUT

Not sure which adjectives tend to go BEFORE the noun?

Then see Short and common adjectives that go BEFORE nouns (adjective position) and Other adjectives that go BEFORE nouns