It's a neuter noun, so how is it not "schoon bord"?
If an adjective comes before a noun with a definite article ("de" or "het"), it gets the ending -e.
[definite article] - [adjective]+[-e ending] - [noun]
That rule only applies to indefinite "het" words: those with an indefinite article, and those without an article or other determiner. "Een schoon bord" but "Het schone bord".
should not be "schoon bord" because it is het bord or is it because is not explicit the "het" at the beginning of the sentence