Wudu Over Henna That Forms A Thin Layer
Whether this layer prevents water from reaching the skin is a technical matter best determined by experts. If it forms a barrier, it would be similar to nail polish in its implications for purification. There are three main scholarly views: If the layer blocks water, Wudu and Ghusl are invalid unless it is removed beforehand. Nail polish is considered part of the hand once applied, so washing the hand with it on still fulfills the requirement. Analogy with Masah on Socks: One may perform Wudu or Ghusl before applying the polish. For subsequent Wudus, washing over the polish would be sufficient—similar to wiping over socks.