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Use of colorimetry for the distinction and classification of 24 species of rosewood and palisander (Dalbergia spp.) from Madagascar

This study demonstrates that colorimetry serves as an effective, low-cost, and objective tool for distinguishing and classifying 24 valuable *Dalbergia* species from Madagascar by analyzing significant variations in color parameters and clustering them into distinct groups based on their visual characteristics.

Original authors: Andry Clarel Raobelina, Ndrianarisoa Manalinarivo Raoby, Gérard Janin, Tahiana Ramananantoandro

Published 2026-08-07

📖 5 min read🧠 Deep dive

CC BY 4.0

Original authors: Andry Clarel Raobelina, Ndrianarisoa Manalinarivo Raoby, Gérard Janin, Tahiana Ramananantoandro

Original paper licensed under CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

Imagine you are a detective trying to solve a mystery, but instead of fingerprints or footprints, your clues are colors. In the world of wood science, this is exactly what researchers do when they try to tell different types of trees apart. For centuries, people have looked at wood and guessed its identity based on whether it looks "reddish," "brown," or "yellow." But human eyes are tricky; one person's "dark red" might be another person's "purple-brown," and our brains can be fooled by lighting or fatigue. To fix this, scientists use a tool called colorimetry. Think of it as a high-tech color camera that doesn't just "see" a color, but measures it with laser precision using a universal language called CIELab. In this system, every color gets a set of three numbers: L (how light or dark it is), a (how red or green it is), and b (how yellow or blue it is). This turns a subjective feeling into an objective fact, like turning a vague description of a sunset into a specific GPS coordinate. This matters because some of the most beautiful and valuable woods in the world are being stolen and sold illegally. If we can't tell them apart quickly and accurately, we can't stop the thieves or protect the trees.

This paper is about a team of scientists in Madagascar who decided to put this color-matching detective work to the test on 24 different species of Dalbergia trees. These trees are famous for producing "rosewood" and "palisander," two types of timber so precious that they are often smuggled out of the country to be made into fancy furniture and musical instruments. The problem is that the names "rosewood" and "palisander" have been used loosely for years, based on old, subjective guesses about what the wood looks like. The researchers wanted to see if they could use a color-measuring machine to create a strict, scientific rulebook to sort these 24 species into their proper groups.

The scientists took tiny, non-destructive samples from 143 individual trees across Madagascar. They sanded the wood smooth and used a special machine to measure the color of the heartwood (the inner, valuable part of the tree) on three different angles: the cross-section, the side, and the end grain. They didn't just look at the wood; they fed the numbers into a computer to see if the colors could sort the species into distinct families.

What they found was a colorful map of the forest. The 24 species didn't all look the same; in fact, their colors varied wildly. The researchers discovered that the wood could be sorted into three main "color families" based on the machine's data:

The Yellowish Group: These woods were lighter and brighter, with a strong yellow tone.
The Brownish Group: These were medium in darkness, leaning toward a reddish-brown hue.
The Reddish Group: These were the darkest woods, with a deep, rich red tone.

This sorting was a big deal because it challenged the old, messy way of naming these woods. For example, some trees that were traditionally called "rosewood" (which implies a specific red color) actually turned out to be in the "yellowish" or "brownish" groups according to the machine. The study suggests that the traditional labels might be wrong for some species. Specifically, the researchers found that four species—D. bathiei, D. maritima, D. normandii, and D. occulta—had colors so close to the famous reference rosewood (D. louvelii) that they could likely be classified as true rosewoods. However, other species that were previously thought to be rosewood actually looked more like "palisander" (the brownish type) when measured objectively.

The study also peeked under the hood to see why the wood was colored the way it was. They looked at the chemical "extractives" inside the wood, which are like the natural dyes trees produce. They found a clear link: the more extractives a tree had, the darker the wood became. However, they ruled out one common suspect: phenols (a type of chemical compound). Even though people often think phenols make wood dark, the data showed that the amount of phenols didn't actually change the color in a predictable way for these trees. It was the total mix of extractives that mattered.

So, what does this mean for the future? The paper suggests that colorimetry is a powerful, low-cost tool that can act as a first line of defense against illegal logging. Instead of relying on a human's guess, customs officers or forest rangers could use a handheld color scanner to quickly sort a piece of wood into one of the three color groups. If a piece of wood is supposed to be a specific type of rosewood but the scanner says it's a "yellowish brown," that's a red flag. While the study admits that more research is needed to cover every single tree and account for differences in soil or climate, it proves that we can move from guessing to knowing. By turning wood color into hard numbers, we can finally give these precious trees the protection they deserve.

Technical Summary: Use of Colorimetry for the Distinction and Classification of 24 Species of Rosewood and Palisander (Dalbergia spp.) from Madagascar

Problem Statement
Madagascar is a primary source of precious timber from the Dalbergia genus, including species commercially designated as "rosewood" and "palisander." These designations are historically based on subjective visual assessments of wood color, which has led to inconsistencies in identification. This subjectivity poses a significant challenge for the enforcement of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES), as "rosewood" commands significantly higher market values than "palisander," driving illegal trafficking. While spectrophotometry has been applied to wood science globally, there is a lack of objective, quantitative databases specifically for the diverse Dalbergia species of Madagascar. Existing studies have focused on consumer aesthetic preferences rather than systematic taxonomic discrimination required for regulatory compliance.

Methodology
The study analyzed 143 wood block samples (2 cm × 2 cm × 2 cm) representing 24 distinct Dalbergia species collected from 143 individual trees across Madagascar. To minimize ecological impact on endangered species, non-destructive sampling was employed.

Sample Preparation: Three wood planes (transverse, radial, and tangential) were sanded to remove machining marks and oxidized layers.
Colorimetric Measurement: A CM-5 spectrophotometer was used to measure color in the CIELab* space under D65 illuminant with a 10° observer angle. Parameters measured included lightness ( $L^*$ ), red-green coordinate ( $a^*$ ), yellow-blue coordinate ( $b^*$ ), chroma ( $C^*$ ), and hue angle ( $h$ ). Six measurements were taken per plane, totaling 18 per block.
Statistical Analysis:
- Two-way ANOVA assessed the effects of species and wood plane on color.
- Pearson and Spearman correlations analyzed relationships between color parameters.
- Classification was performed using three methods: (1) Camargos and Gonçalez (2001) color table; (2) Color difference ( $\Delta E^*_{ab}$ ) calculations against reference species (D. louvelii for rosewood and D. chlorocarpa for palisander); and (3) Hierarchical Ascending Clustering (HAC).
- Correlation analysis was conducted between color parameters and chemical data (extractive and phenol content) from a previous study (Razafimahatratra et al., 2019).

Key Results

Color Variability: Significant differences in colorimetric coordinates were observed across the 24 species ( $p < 0.05$ ). Luminance ( $L^*$ ) ranged from 28.08 to 58.43, with most species exhibiting dark heartwood ( $L^* < 56$ ). The radial plane generally exhibited higher luminance and saturation compared to tangential and transverse planes.
Species Homogeneity: Dalbergia normandii was the only species showing no significant colorimetric variation across the three wood planes.
Correlations: A strong positive correlation was found between luminance ( $L^*$ ) and the yellow coordinate ( $b^*$ ), indicating that lighter woods tend toward yellow hues. Extractive content showed a negative correlation with luminance ( $L^*$ ), suggesting that higher extractive content results in darker wood. Phenol content did not significantly correlate with color parameters.
Classification Outcomes:
- Camargos and Gonçalez Table: Grouped species into four categories: reddish-brown (1 species), dark-brown (11 species), purplish-brown (5 species), and reddish-black (5 species), with 2 species remaining unclassified.
- Reference Comparison: Using $\Delta E^*_{ab}$ against D. louvelii, four species (D. bathiei, D. maritima, D. normandii, D. occulta) showed close resemblance, supporting their classification as rosewoods.
- Hierarchical Clustering (HAC): Successfully divided the 24 species into three distinct groups based on color dominance:
  1. Yellowish: High $L^*$ , high $C^*$ , $h > 45^\circ$ (e.g., D. orientalis, D. monticola).
  2. Brownish: Moderate $L^*$ , high $a^*$ , $35^\circ < h < 38.52^\circ$ (e.g., D. lemurica, D. suaresensis).
  3. Reddish: Low $L^*$ ( $31 < L^* < 33.2$ ), low $C^*$ , $35^\circ < h < 36.8^\circ$ (e.g., D. louvelii, D. bathiei, D. normandii).

Significance and Claims
The authors claim that colorimetry serves as a promising, low-cost, and objective tool for distinguishing Dalbergia species, offering a scientific alternative to traditional subjective visual assessments. The study establishes the first objective database for the wood color of Malagasy Dalbergia species, which is critical for CITES enforcement. By enabling the initial clustering of species into color-based groups (yellowish, brownish, reddish), the method facilitates a preliminary screening process before more complex identification techniques are applied. The findings suggest that while some species traditionally labeled as rosewood (e.g., D. baronii) may be more accurately classified as palisander based on their yellowish hues, others (e.g., D. occulta) align closely with the reddish characteristics of true rosewood. The authors conclude that this approach lays the groundwork for integrating colorimetry into regulatory frameworks to combat illegal timber trade, while acknowledging limitations regarding sample size and the need for future chemical analysis to fully understand the phytochemical drivers of color.

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