Steaming and holding before preservative treatment by the Bethell process greatly improved the treatment of radiata pine heartwood. Maximum penetration of preservative for the shortest holding period was obtained by the use of steam vacuum but the difference between this and steam venting was small when compared with the standard of treatment of air dried samples. A holding period of one day was sufficient to obtain virtually complete penetration of preservative during subsequent treatment of samples which had been steam vacuum seasoned. To obtain similar penetration in steam vented samples holding period would have had to be in excess of four days.

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