per saltire

To add variety and interest to the arms, heraldic artists began to divide the background of the shield into two parts, giving each a different colour. They were named for the ordinary that they most resembled, so the division of the shield by opposing diagonal lines, similar to the ordinary known as the saltire came to be called per saltire Understanding Signs & Symbols – Heraldry, S. Oliver & G. Croton, Quantum, London, 2013, P63. Visually rather striking, it became popular and artists added decorative effects to the partition line to distinguish otherwise very similar coats of arms. A Glossary of Terms used in British Heraldry, J.H. Parker, Oxford, 1894, Entry:Party.