Bog oak
As Mooreichen are oak logs ( Quercus spp. ) Over a period of centuries or millennia in designated bogs have been lying or wetlands. A reaction of iron tannins inside the trunk discolors and hardens the wood and changes its physical, chemical and structural properties.
description
Bog oaks are found when peat bogs are drained or bog cultivation and bog colonization measures . One speaks of sub-fossil oak ( Quercus spp. ). The tannic acid contained in the wood combines with the iron salts of the moor water over time, which leads to discoloration and hardening of the wood.
The discoloration varies from light gray to dark yellow, dark brown, blue-gray to deep black and is very irregular. Most of the trunks found are 3 to 20 m long and up to 1.3 m in diameter. The age of the subfossil oak trunks is between 600 and up to 8,500 years.
Emergence
Subfossil oak is produced from recent oak by long storage in the absence of oxygen in boggy or swampy areas. The change is a slow, protracted process of an iron tanning reaction of the tannic acid-containing wood and the iron-rich, moist soils and waters, as well as the ammoniacal swamp gases in the area. The prevailing storage conditions determine the degree of color change, intensity and other changes in the wood properties.
Chemical degradation is relatively insignificant during long storage and occurs predominantly with the polyoses of the wood. In the electron microscope image, the increase in the hydrolysis-resistant portion becomes clear due to the higher electron absorption of the cell wall . Only a slight breakdown of the cell wall can be seen at the edge of the lumen .
processing
Subfossil oak is found by chance. It is usually extracted from the ground using simple methods and then sold. Machining with mechanical methods still works well, all that needs to be considered are possible wood defects such as twisted growth, curvatures, out-of-roundness, core rot, hollow stem, ring peeling, non-core zones or uneven tree ring widths. These should be included in the marker planning.
The subsequent drying should be carried out extremely gently and slowly, otherwise cracks can form quickly.
Gluing the wood works well and can be carried out without any problems using common adhesives. A surface treatment is also easy to carry out and the wood can be painted.
Bog oak is easy to saw, plan, mill, drill, grind, turn or process into veneer. Common finishing methods are halving, quartering, upright and multiple division, but the bog oak is then usually processed into veneer wood, especially cut wood for face veneer for furniture, paneling, parquet or as special wood for turning. The wood utilization is around 95%.
Wood quality and properties
Difference between subfossil and recent oak
Subfossil oak / bog oak
The properties of subfossil oak do not differ significantly from those of recent oaks. The fermentation density according to DIN 52182 is a little higher on average and is around 0.58 to 0.73 g / cm³. The average density is also slightly higher than that of recent oak and is around 0.62 to 0.76g / cm³. Like recent oak, subfossils are only moderately dwindling.
The wood properties such as hardness, weight, machinability vary and depend on the location and the age of the respective piece.
Mechanical processing can be carried out well, only caution is required when screwing, because screws should be pre-drilled.
In order to prevent cracking, emphasis should be placed on slow, gentle drying. With regard to durability, it should be noted that bog oak is not weatherproof and only moderately resistant to fungal or insect attack.
Recent oak
The average kiln density according to DIN 52182 for recent oak is lower than for subfossil oak and is approx. 0.48 to 0.87g / cm³. The average density is also slightly lower than that of subfossil oak and is approx. 0.55 to 0.98g / cm³. Recent oak wood also only shrinks moderately.
In this case, wood properties such as hardness, weight and workability vary depending on the location and age. Recent oak is generally easy to work with, it can be knifed, peeled and split easily. However, it is difficult to plane due to its coarse grain. For installation with screws or nails, thin wood should be pre-drilled.
As with subfossil oak, recent oak also tends to crack and throw, so drying should be carried out gently and slowly even with recent oak.
Physical, chemical and structural properties
Bog oak / subfossil wood
Bog oak is a moderately shrinking wood. The properties of the pieces found, such as hardness, weight and machinability, depend on the location and age. Wagenführ (2007) gives the following parameters for oak (Quercus robur L.) subfossil wood.
- Density: 0.58 ... 0.63 ... 0.73 g / cm³
- Density (wood moisture 12%): 0.615 ... 0.665 ... 0.760 g / cm³
- Maximum rate of shrinkage lengthways: 0.2 ... 0.5 ... 0.7%
- Maximum shrinkage rate radial: 6.5 ... 8.0 ... 13.7%
- Maximum shrinkage rate tangential: 6.9 ... 11.9 ... 13.9%
When investigating subfossil oak wood, the ash content increases from the inside of the trunk to the outside; this is related to the transport of the mineral components via diffusion into the inside of the trunk. The ash content of bog oak is generally higher than that of recent wood. Wagenführ (2007) gives 0.8% to 1.5% ash content for bog oak. As the darkening increases, the modulus of elasticity of the subfossil wood decreases.
For comparison, recent oak wood
Even freshly felled oak shrinks only moderately and here, too, the properties such as hardness, weight and workability are clearly subject to fluctuations in terms of the location and age, Wagenführ (2007) gives the following parameters for oak (Quercusrobur L.) recent wood.
- Density: 0.39 ... 0.65 ... 0.93 g / cm³
- Density (wood moisture 12%): 0.43 ... 0.69 ... 0.96 g / cm³
- Maximum rate of shrinkage lengthways: 0.4%
- Maximum shrinkage rate radial: 4.50 ... 4.67%
- Maximum shrinkage rate tangential: 7, 8 ... 10.0%
Ash content for recent wood 0.3% to 0.6%
Trade and use
Due to its characteristic color and properties, the bog oak wood is in demand, for example for pipe makers who use it to build high-quality and high-priced pipes. Craftsmen also use bog oak to use it as veneer for furniture, musical instruments, paneling and other things. Bog oak is popular with artists who use subfossil oak in their work. Because of its rarity, bog oak is in demand and high prices are charged. The prices vary greatly, influenced by the age and condition of the piece.
literature
- R. Wagenführ: Types of wood information sheet on subfossil oak. In: wood technology. ( IHD ). Volume 48, No. 6, pp. 2-3.
- K. Kranitz, E. Baradit, E. Dobrowolska, M. Plötze, P. Niemz: Investigations on properties of bog oak . In: wood technology. (IHD). Volume 53, No. 1, pp. 11-17.
- K. Kranitz, E. Baradit, E. Dobrowolska, M. Plötze, P. Niemz: Physical, chemical and structural properties of recent and subfossil oak. In: WOOD as a raw material. No. 32, Springer Verlag 1974.
Web links
- Bog oak data sheet. Retrieved December 19, 2016 .
- Oak data sheet. Retrieved December 19, 2016 .
- Dealer for pipes made of bog oak. Retrieved December 19, 2016 .
Individual evidence
- ↑ a b c Bog oak data sheet. Retrieved December 19, 2016 .
- ↑ a b Species of wood information sheet on subfossil oak. In: R. Wagenführ: Wood technology. (IHD). Volume 48, No. 6, pp. 2-3.
- ↑ K. Kranitz, E. Baradit, E. Dobrowolska, M. Plötze, P. Niemz: Investigations on properties of bog oak . In: wood technology. Volume 53, No. 1, pp. 11-17.
- ↑ a b c K. Kranitz, E. Baradit, E. Dobrowolska, M. Plötze, P. Niemz: Physical, chemical and structural properties of recent and sub-fossil oak. In: WOOD as a raw material. Volume 32, Springer Verlag 1974.
- ↑ Oak data sheet. Retrieved December 19, 2016 .
- ↑ Dealer for pipes made of bog oak. Retrieved December 19, 2016 .