Bones can blacken due to several factors, not just one single cause. The discoloration isn't inherently a sign of decay or disease, though it can sometimes be associated with these processes. Let's explore the main reasons why bones may turn black:
Causes of Bone Blackening
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Burning: High temperatures, such as those from a fire, can significantly alter bone structure, leading to a black coloration. This is a result of the charring process that occurs at elevated temperatures (over 645°C), changing the bone's mineralogy. (Marin Arroyo et al., 2008; Shahack-Gross et al., 1997; Stathopoulou et al., 2013)
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Mineral Staining: The surrounding environment can play a significant role. Minerals present in soil or water can leach into the bone, causing staining. This staining can range in color, with black being a possible outcome. (Marin Arroyo et al., 2008; Shahack-Gross et al., 1997; Stathopoulou et al., 2013)
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Decomposition of Organic Components: As bones decompose, the organic components within them break down. This process can lead to discoloration, including blackening, through a combination of bacterial activity and chemical changes. (Marin Arroyo et al., 2008; Shahack-Gross et al., 1997; Stathopoulou et al., 2013)
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Bacterial Activity During Degreasing: In the process of degreasing bones (e.g., in bone collecting), active bacteria can cause black discoloration. This is particularly true if the bones are still greasy or haven't been properly cleaned. Continuing the degreasing process with appropriate methods such as ammonia and water can often resolve this issue. (Reddit r/bonecollecting and r/vultureculture threads)
Examples and Practical Insights
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Archaeological Finds: Blackened bones found in archaeological contexts often result from a combination of factors, including burning, mineral staining from the surrounding soil, and long-term decomposition.
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Bone Collection: Bone collectors often encounter blackening during the cleaning and degreasing process. Proper cleaning techniques are crucial to prevent unwanted discoloration.
The blackening of bones isn't always a cause for concern, as it's often a natural process or a result of environmental factors. However, understanding the potential causes can be helpful in interpreting the history and condition of the bones.
