Structure and properties of balsawood of a Slovenian trader

Na vzorcih lesa s trgovskim imenom balza izbranega slovenskega trgovca smo proučili zgradbo in določili izbrane lastnosti, da bi ugotovili ali res kupujemo les balze (Ochroma lagopus Sw.). Opravili smo makroskopsko in mikroskopsko identifikacijo ter določili osnovno gostoto lesa, delež celičnih sten in volumske skrčke. Iz lesa smo izdelali trajne preparate, ki smo jih preučili pod svetlobnim mikroskopom in identificirali s pomočjo identifikacijskih ključev. Osnovno gostoto, definirano kot maso absolutno suhega lesa na maksimalni volumen, smo določili s pomočjo tehtanja ter volumetriranja. Delež celičnih sten smo izmerili na preparatih prečnih prerezov s pomočjo mikroskopa in programa NIS Elements BR 3.0. Za določitev totalnih volumenskih skrčkov smo določili maksimalni volumen in volumen v absolutno suhem stanju. Identifikacija lesa je potrdila, da so vsi preizkušanci pripadali lesu balze (Ochroma lagopus Sw.). Osnovna gostota je variirala od 62 kg/m3 do 328 kg/m3. Delež lumnov je znašal od 28 % do 52 %. Volumenski skrčki so bili od 7,4 % do 28,8 %, medtem ko je 60 % preizkušancev pri sušenju do absolutno suhega stanja kolabiralo.The samples of wood with the trade name balsa obtained from a Slovenian trader were used to investigate the structure and to determine selected properties of wood. We wanted to find out if we are really buying the wood of balsa (Ochroma lagopus Sw.) On the selected samples, we made macroscopic and microscopic wood identification, and determined basic density, proportion of cell walls and volume shrinkage. To identify wood we made permanent slides, which were examined under a light microscope, and identified by using microscopic wood identification keys. We set the basic density, defined as the mass of oven dry wood per its maximal volume. Proportion of cell walls was measured on cross-sections observed under the light microscope using the programme NIS Elements BR 3.0. To determine the total volume shrinkage, we measured the volume of wood having moisture content above the fibre saturation point and oven dry wood. Identification has revealed that all the samples belonged to wood of balsa (Ochroma lagopus Sw.). The basic density varied from 62 kg/m3 to 328 kg/m3. The proportion of lumens was from 28 % to 52 %. The volume shrinkage was 7.4 % to 28.8 %, while 60 % of the samples collapsed during drying