What is the criterion for determining whether paint prevents water from reaching the skin during ablution (wudu'), and are olive oil or petroleum jelly considered to have a substance that prevents this?

For the validity of purification, it is a condition to remove anything that prevents water from reaching the limbs of ablution in the minor ritual impurity, and from reaching the entire body in the major ritual impurity, unless its removal is difficult or causes harm. So, if wax, dough, or henna prevents water from reaching a limb, the purification is not valid, whether the obstructing substance is little or much. However, if only the trace and color of henna remain without its substance, or the trace of a fluid oil such that water touches the skin and flows over it, then the purification is valid. The consideration is for water reaching and penetrating the body, not for its permanence and stability on the limb.