Treatment of hardwood articles with copper and/or zinc wood preservatives

A method of treating tyloses-containing hardwood railroad crossties and tyloses-containing hardwood railroad switch ties containing mixed tyloses-containing hardwoods including white oak heartwood;

• said method comprising
• placing the tyloses-containing hardwood railroad crossties or tyloses-containing hardwood railroad switch ties, both including white oak heartwood, in a treating vessel comprising a pressure vessel;
• subjecting the tyloses-containing hardwood railroad crossties or tyloses-containing hardwood railroad switch ties, both including white oak heartwood to steam for a period of time,
• subjecting the tyloses-containing hardwood railroad crossties or tyloses-containing hardwood railroad switch ties, both including white oak heartwood, to a vacuum for a period of time,
• supplying a preservative composition comprising an ammoniacal compound including ammoniacal copper zinc arsenate to the treating vessel so that the preservative composition will contact a least one surface of the tyloses-containing hardwood railroad crossties or tyloses-containing hardwood railroad switch ties, both including white oak heartwood, and
• penetrating the preservative composition below the surface of the tyloses-containing hardwood railroad crossties or tyloses-containing hardwood railroad switch ties, both including white oak heartwood, in an amount sufficient to inhibit insect and fungal attacks at an average depth of at least 0.5 inches as determined following American Wood Protection Association M2-07 Standard,
• wherein penetrating the preservative composition into the tyloses-containing hardwood railroad crossties or tyloses-containing hardwood railroad switch ties, both including white oak heartwood, comprises applying pressure to the treating vessel containing the tyloses-containing hardwood railroad crossties or hardwood railroad switch ties, both including white oak heartwood, and the preservative composition for a period of time.