BRIEF ORIGINAL Comparing two internal check measurement methods for wood drying quality assessment Khamtan Phonetip 1,3 • Barbara Ozarska 1 • Graham Ian Brodie 2 Received: 2 June 2016 / Published online: 25 October 2016 Ó Springer-Verlag Berlin Heidelberg 2016 Abstract Internal checks that are created in the interior of lumber during or after timber drying seriously affect the quality and value of timber used for the production of high value wood products. This study compared two different methods of assessing wood drying quality, by using either an image analysis ImageJ or Digital Calliper technique, to determine the percentage loss of cross section due to internal checking. The study revealed that there was a significant difference in the total area of internal checks, but the overall timber quality classes determined from both techniques were identical based on the Australian and New Zealand standard for timber quality assessment. 1 Introduction Internal checks or honeycomb are only formed when the internal tension stress during seasoning exceeds the tensile strength perpendicular to fibre direction. It occurs when the core moisture content is high and the applied drying temperature is relatively high (Simpson 2001). Internal checking is one of the most important parameters for determining timber grading classes, as described in the Australian and New Zealand standard of timber quality AS/ NZS 4787 (2001). Internal checks can result in losses of timber volume during the manufacturing of wood products because this defect usually cannot be readily seen as it does not appear on the surface of boards (Simpson 2001). Affected timber often needs to be discarded due to the manufacturing process revealing internal checks. Internal checks have been assessed and studied by many researchers by using varied methods of determining the check area (Mekhtiev and Torgovnikov 2004; Harris et al. 2008; Yuniarti et al. 2015). There are many software options available for determining wood defects. Harris et al. (2008) used Image-Pro Plus version 6 software to identify the surface checks from the perimeter of wood samples. Mekhtiev and Torgovnikov (2004) used ImageJ software for analysing the check area of wood samples, which were treated by microwave, through analysis of scanned images with 1200 dpi resolution. However, the most common method used by researchers (Yuniarti et al. 2015) and industries for measuring the area of internal checks was based on the width and length of checks using the Digital Calliper method. This method is used for grading the timber according to the standard for drying quality class. It is important to highlight that grading of timber is vital for the wood processing industries because the price of timber is based on the grade to which the boards are assigned. For example, internal checking was one issue listed in complaints that led to product replacement from 41 mills in Victoria and Tasmania in 2009. It is believed & Khamtan Phonetip khamtanfof@gmail.com 1 School of Ecosystem and Forest Sciences, Faculty of Science, The University of Melbourne, Burnley Campus, 500 Yarra Boulevard, Richmond, VIC, Australia 2 Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Nalinga Rd, Nalinga Rd, Dookie, VIC 3647, Australia 3 Department of Forest Economics and Wood Technology, Faculty of Forestry Science, The National University of Laos, DongDok Campus, Xaythany District, Vientiane, Lao People’s Democratic Republic 123 Eur. J. Wood Prod. (2017) 75:139–142 DOI 10.1007/s00107-016-1115-1