According to Genesis, pitch was placed around Noah's Ark to make it watertight.
Genesis 6:14 tells Noah to cover the ark with pitch inside and outside. Pitch is a thick, waterproofing substance traditionally made from tar-like or resinous materials. The biblical Hebrew word is related to a term for covering or atonement, which has led to discussion about its linguistic background as well as its practical function.
The instruction matters because the vessel is described as a wooden structure intended to survive floodwaters. Pitch would seal gaps in the timber and reduce water entering through joints. Genesis does not give a recipe, source, or precise application technique.
Modern depictions sometimes show the ark as painted or coated with ordinary black tar, but that is an artistic approximation. The text specifically names pitch and says it was applied both inside and outside, a detail distinct from the wood used to build the ark.