An Introduction to Bilinga (Opepe)
Bilinga, commonly known in the timber trade as Opepe, refers to African timber predominantly derived from Nauclea diderrichii (along with recognized botanical synonyms including Sarcocephalus diderrichii, Nauclea trillesii, Nauclea gilletii, Nauclea xanthoxylon, and Sarcocephalus xanthoxylon). Documented extensively by the French research institute CIRAD Tropix, this species originates from tropical Africa and provides substantial log diameters ranging from 60 to 90 cm. For custom furniture builders and epoxy river table craftsmen, Bilinga offers an intense visual presence paired with dense, heavy-duty mechanical performance.
Visual Character, Grain, and Figure
The heartwood of Bilinga is recognized by its vibrant orange-yellow or golden-yellow coloration, which frequently exhibits a slightly moiré optical effect. The sapwood is clearly demarcated from the heartwood, displaying a thickness of 3 to 5 cm. In terms of texture, the wood is medium, but its defining working characteristic is a marked interlocked grain. This ribbon-like interlocking creates dynamic light reflection across the slab face, though it also introduces specific behavioral challenges during prep and surfacing.
Density, Weight, and Hardness
Bilinga is a dense hardwood with a standard specific gravity of 0.76 at 12% moisture content. In working shop terms, this translates to a density of approximately 47.4 lb/ft³. A surfaced 2-inch-thick river table slab weighs roughly 7.9 lb per square foot before accounting for the epoxy channel.
On the French Monnin hardness scale, Bilinga registers at 5.3 at 12% moisture content. The Monnin scale is a standard European test where higher numbers indicate harder timber; it should not be confused with or converted into a Janka hardness rating. Mechanically, Bilinga provides exceptional rigidity and crush resistance, recording a crushing strength of 63 MPa (about 9,140 psi), a static bending strength of 95 MPa (about 13,780 psi), and a modulus of elasticity of 14,660 MPa (about 2,126,000 psi).
| Property | CIRAD Tropix value | What it means / US units |
|---|---|---|
| Botanical name(s) | Nauclea diderrichii, Sarcocephalus diderrichii (synonymous), Nauclea trillesii (synonymous), Nauclea gilletii, Nauclea xanthoxylon, Sarcocephalus xanthoxylon (synonymous) | |
| Colour / texture / grain | Orange yellow; texture medium; grain interlocked; interlocked grain marked | |
| Specific gravity (12% MC) | 0.76 | about 47.4 lb/ft³; a 2-inch-thick slab weighs about 7.9 lb per sq ft |
| Monnin hardness (12% MC) | 5.3 | French hardness scale; higher = harder (not a Janka value) |
| Total tangential shrinkage | 7.5 % | green to oven-dry |
| Total radial shrinkage | 4.5 % | green to oven-dry |
| Ratio St/Sr | 1.7 | closer to 1 = less cupping tendency |
| Coefficient of volumetric shrinkage | 0.55 % per % MC | volume change per 1% change in moisture content |
| Fibre saturation point | 25 % | |
| Thermal conductivity | 0.25 W/(m·K) | |
| Crushing strength (12% MC) | 63 MPa | about 9,140 psi |
| Static bending strength (12% MC) | 95 MPa | about 13,780 psi |
| Modulus of elasticity (12% MC) | 14,660 MPa | about 2,126,000 psi |
| Decay (fungi) resistance | Durability class 1 – very durable | |
| Termite resistance | Class D – durable | |
| Dry-wood borer resistance | Class D – durable (sapwood demarcated, risk limited | |
| Heartwood treatability | Class 2 – moderately permeable | |
| Use class from natural durability | Class 4 – in ground or fresh water contact | |
| Drying | rate slow; distortion: slight risk; checking: risk of surface splitting in outdoor uses in dry, hot environments; collapse: no known specific risk; casehardening: no known specific risk | |
| Suggested kiln program temperatures | 53–65 °C | about 127–149 °F |
| Machining | blunting normal; saw teeth: ordinary or alloy steel; cutting tools: ordinary | |
| Nailing and screwing | Good but pre-boring necessary | |
| CITES status | This species is not listed in the CITES Appendices (Washington Convention 2025). Notes. * Common commercial name |
Values from the CIRAD Tropix technical sheet (average values for mature wood, 12% moisture content where noted). US-unit conversions are calculated by BigEpoxy (1 MPa = 145.04 psi; density = specific gravity × 62.43 lb/ft³).
Shrinkage, Wood Movement, and the Epoxy River Interface
The CIRAD Tropix technical sheet classifies Bilinga as a moderately stable wood. Understanding its dimensional movement is critical when casting rigid polymer resins directly against a live edge:
- Total tangential shrinkage (St): 7.5%
- Total radial shrinkage (Sr): 4.5%
- Tangential to radial ratio (St/Sr): 1.7
- Coefficient of volumetric shrinkage: 0.55% per 1% change in moisture content
- Fibre saturation point (FSP): 25%
A shrinkage ratio of 1.7 indicates a moderate risk of cupping across wide flat-sawn planks. When building an epoxy river table, any dimensional expansion or contraction puts sheer stress on the epoxy-to-wood bond line. Because the volumetric shrinkage rate is 0.55% per percent of moisture variation, the slab must be properly conditioned to the target indoor equilibrium moisture content prior to pouring resin. If thick boards are cast while carrying residual moisture, subsequent drying inside an air-conditioned or heated home can induce stress checks or jeopardize the river seam.
Drying Behavior and Shop Risks
CIRAD notes that Bilinga has a slow drying rate and is explicitly difficult to dry due to its marked interlocked grain. While there is only a slight risk of distortion and no known specific risk of collapse or casehardening, the wood exhibits a risk of surface splitting in outdoor settings subjected to dry, hot environments. For kiln operations, suggested drying schedules utilize mild to moderate temperatures starting around 50 to 53 °C and topping out at 65 °C (approximately 127 to 149 °F).
Machining, Fastening, Gluing, and Finishing
Working Bilinga in the shop presents a balanced set of machining attributes:
- Tooling: The blunting effect on cutters is rated as normal, and the species can be worked using ordinary cutting tools as well as ordinary or alloy steel saw teeth.
- Fasteners: Nailing and screwing hold well, but pre-boring is necessary due to a slight tendency for the timber to split under fasteners.
- Gluing considerations: CIRAD notes that Bilinga wood is acidic, which must be taken into account when selecting adhesives and preparing bonding faces. Surface prep must ensure clean, sound wood fibers along the river interface.
- Finishing: CIRAD explicitly notes that Bilinga needs pore filling before polishing to achieve a smooth, high-sheen furniture surface.
Natural Durability and CITES Status
Bilinga exhibits natural durability. Its heartwood achieves Durability Class 1 (very durable) against wood-decay fungi and Class D (durable) against dry-wood borers and termites. Naturally meeting Use Class 4 (in ground or fresh water contact) and European standards for Use Class 5 (marine water exposure), the species resists biological breakdown. Commercial end-uses cited in the data sheet range from high-class cabinetwork and furniture components to flooring, interior joinery, heavy carpentry, and sliced veneer. Furthermore, Bilinga is not listed in the CITES Appendices (Washington Convention 2025).
Is It a Good Epoxy Table Wood?
Bilinga makes a striking, durable tabletop material for epoxy river builds, provided the woodworker respects its physical constraints. Its golden-to-orange-yellow coloration and moiré figure yield a visual result rarely matched by domestic species, while its 5.3 Monnin hardness provides superior dent resistance. However, builders must account for its marked interlocked grain during surfacing, use pore filler before final clear coating, and accommodate its natural wood acidity during adhesive and resin prep.
Sources
Published October 30, 2026. Sources are linked in the text.
Header image: original graphic by BigEpoxy.com.
Staff note: According to the CIRAD sheet, Bilinga heartwood is classified as Class 2 (moderately permeable) for preservative treatability, and the logs do not float in water, which underscores the material’s sheer bulk when unloading whole slabs. (Source: CIRAD Tropix 7 technical sheet: Bilinga / Opepe*.)