Many believe human bones completely vanish into fine ash during cremation, similar to wood burning. However, the transformation of bone structure under intense heat is a more nuanced scientific process. This process yields a substance different from the ash produced by burning organic materials.
The Building Blocks of Bone
Bones have a complex composition, providing both strength and flexibility. They are a composite material, made of organic and inorganic components. The organic phase primarily consists of collagen, a protein forming a flexible framework, similar to rebar in concrete. Collagen makes up about 30-40% of bone, contributing to its tensile strength and elasticity.
The inorganic component, accounting for roughly 60-65% of bone’s dry weight, is predominantly calcium phosphate. This mineral phase provides bones with their characteristic hardness and rigidity. This dual nature—a flexible protein matrix infused with a hard mineral—is fundamental to understanding its behavior during cremation.
Bone Transformation During Cremation
When a body undergoes cremation, it is placed in a specialized chamber where temperatures typically range between 1,400 to 1,800 degrees Fahrenheit (760 to 982°C). At these extreme temperatures, the organic components of the body, including soft tissues, organs, water, and the collagen within the bones, vaporize. This process removes all combustible materials, leaving behind only the skeletal structure.
The remaining inorganic mineral structure then undergoes calcination. During this process, intense heat dehydrates and decomposes the bone, transforming calcium phosphate into a more stable form. This high-temperature exposure makes the bones very brittle and susceptible to fragmentation. The bone’s color also changes; organic components carbonize, turning bones brown or black, before converting to a light gray or white appearance at higher temperatures.
Understanding Cremated Remains
The material returned to families after cremation is not a fine, powdery ash like that from burnt wood. Instead, these are primarily bone fragments that have been processed to a consistent texture. After the cremation chamber cools, the remaining bone pieces, which are now very fragile, are collected. Any non-consumed items, such as certain metal implants, are separated from the bone fragments.
These brittle bone fragments are then placed into a machine called a cremulator, which grinds them into a uniform substance. The resulting material resembles coarse sand or fine gravel. The color of these cremated remains is typically light gray or white, though variations to off-white, beige, or darker gray can occur depending on factors like cremation temperature and bone density. Chemically, these remains consist mostly of dry calcium phosphates, along with trace amounts of other minerals like sodium and potassium salts.