Is ink considered a barrier to water during Wudu, and what should be done if its removal is difficult?

The impediment that prevents the validity of ablution is that which has a physical body (jirm) preventing water from reaching the skin. Ink is not like that; rather, it is merely a color that does not prevent the validity of ablution because it has no physical body. The determining factor is whether something prevents water from reaching the skin. If it does not prevent, then ablution is permissible; but if it does prevent, then it is not permissible.