According to Genesis, Noah coated the Ark with pitch inside and outside.
Genesis 6:14 tells Noah to cover the ark with pitch, using the same instruction for its interior and exterior surfaces. Pitch is a waterproofing substance made from tar-like or resinous material, so the command fits the practical need to keep water out of a wooden vessel.
The Hebrew word translated as “pitch” is related to the language of covering or atonement in some interpretations, but the immediate construction context concerns sealing the ark. English Bibles may differ slightly in wording while retaining the idea of waterproof coating.
The passage does not specify the exact source, recipe, or quantity of the pitch. It also does not say that the ark was painted a particular color. Those details belong to later artistic reconstructions, while Genesis provides the concise instruction to coat both sides.