Flotation
Definition
Passing grave fill through water to separate organic material that floats (seeds, plant fragments, insect remains, charcoal) from heavier inorganic material that sinks and is retained on a fine mesh.
- Purpose
- Recovers organic macro-remains (seeds, charcoal, insect parts) from grave fill
- Method
- Fill submerged or agitated in water; light fraction floats off
- Retention
- Fine mesh, typically 250-500 micron, catches the floating fraction
- Common use
- Buried remains, arson debris and mass grave excavation
Common questions
Why not just hand-pick material from the soil instead of flotation?+
Small carbonised seeds, charcoal fragments and insect exoskeletons are easy to miss by eye against soil, especially in dark or clay-rich fill. Water separation exploits the density difference so light organic material rises reliably, giving far more complete recovery than visual sorting alone.
Does flotation damage fragile evidence like insect remains?+
Gentle agitation is used rather than vigorous washing, and the light fraction is dried carefully afterward. Fragile items such as puparia can still fracture, so entomologists often prefer hand-collection at the scene when timing evidence is the priority, reserving flotation for bulk fill processed later.
What happens to the heavy fraction that sinks?+
It is retained on the mesh along with any inorganic material of interest, such as small bone fragments, artefacts or gravel, and is examined separately from the floated organic fraction rather than discarded.
Related terms
- Half-Sectioning
- Dividing the grave along its long axis and excavating one half as a section face before opening the other half. Provides a...
- In-Situ Recovery
- The documentation and removal of evidence from its original position before any surrounding material is shifted. Requires that position, orientation, and associations...
- Sequential Pedestal Method
- An excavation technique where the grave fill is removed in spits around the body, leaving the remains elevated on undisturbed matrix until...
- Taphonomy
- The systematic modification of bone by environmental processes after death, operating over the burial or exposure interval. Includes weathering, soil staining, sun...
- Wet Sieving
- The process of washing material through a mesh with water to separate and recover small fragments. Preferred for fire debris that has...