Cremation is a method of final disposition that uses heat to reduce a human body. Many people imagine the process results in a soft, fine powder of ash, similar to what remains after wood burns. However, the physical and chemical reality is more complex, particularly concerning the skeletal structure. Bones do not combust like other tissues, leaving behind durable fragments that require further processing.
The Mechanics of Cremation
The reduction of the body occurs inside a furnace, often called a retort or cremation chamber. This chamber is lined with heat-resistant bricks and operates at high temperatures, typically ranging from 1,400 to 1,800 degrees Fahrenheit. The body, usually placed within a combustible container, is exposed to this environment for two to three hours.
Exposure to heat rapidly causes the vaporization of the body’s high water content. Following this, thermal energy reduces the soft tissue, including fat, muscle, and organs, through oxidation. This organic matter converts into gases like carbon dioxide and water vapor, which are vented through the furnace’s exhaust system. This phase efficiently reduces the majority of the body’s mass, leaving behind the heat-resistant skeletal structure.
The Transformation of Bone
Unlike soft tissues, bone does not burn because its chemical composition resists flame. Human bone is a composite material, with its strength derived from a mineral component called bioapatite, a form of calcium phosphate. The heat causes the bone to undergo a physical and chemical change known as calcination.
During calcination, high temperatures remove all remaining organic components, such as collagen, and any bound water within the bone matrix. This leaves behind a sterile, brittle mineral residue, which is essentially the pure calcium phosphate structure. The resulting material is not true ash, but rather a collection of lightweight, fragile bone fragments. This calcified residue changes color from its natural state to a pale gray or white, indicating the complete loss of organic material.
Processing the Cremated Remains
Once the thermal reduction phase is complete, the cremation chamber must cool before the operator collects the remaining calcified material. The fragments are then swept from the retort and placed into a collection pan for final preparation. At this stage, the remains are still coarse and recognizable as bone fragments, not the fine substance families expect to receive.
Before processing, foreign, non-bone material must be removed, typically using a powerful magnet. This separates surgical implants, such as hip pins, screws, dental fillings, or other medical hardware that resisted the heat. The remaining bone fragments are then transferred into a cremulator or processor. This device uses rotating blades or grinding elements to mechanically reduce the coarse, brittle fragments into a uniform, fine powder. The final product, commonly referred to as “ashes” or “cremains,” is this fine, sand-like material returned to the family.