Panels that utilize what are known as "back slats" — cross members that are dovetailed into the back of the boards that make up the panel to prevent warping during the drying process and to ensure structural integrity over time — are usually older than 1880/1890. Subsequent to 1880/1890, advances in materials negated the need for these cross members, thus, are seen either on icons painted after this time period when the intent of the artist was to deceive by creating an "older looking" icon, or on icons which are rendered according to traditional means as a way of honoring the old processes. Back slats are sometimes necessary on newer icons of large size for the same reasons (warping and stability) as existed pre-1900.