Ashing
Definition
The terminal stage of heat damage, above approximately 400 degrees Celsius, in which carbon oxidises to carbon dioxide and only inorganic mineral residue (calcium carbonate, silica) survives; writing is generally destroyed at this stage.
- Temperature threshold
- Above roughly 400 degrees Celsius
- Process
- Carbon oxidises to carbon dioxide
- Residue
- Inorganic mineral, e.g. calcium carbonate, silica
- Document effect
- Writing generally destroyed
Common questions
If writing is destroyed at the ashing stage, why do examiners still recover text from burnt documents?+
Recoverable text usually comes from paper that charred but stopped short of full ashing, where carbonisation preserved the ink-substrate contrast; once true ashing occurs the mineral residue is too fragile and undifferentiated to hold legible marks.
How can an examiner tell whether a burnt page reached the ashing stage or stopped at charring?+
Ashed material is typically pale grey or white, brittle, and crumbles rather than holding sheet form, while charred but unashed paper stays black, retains some structural integrity, and can sometimes still be handled and imaged.
Related terms
- Charring
- The stage of heat damage at approximately 200 to 400 degrees Celsius at which paper cellulose converts to amorphous carbon; the sheet...
- Consolidant
- A dilute polymer solution (Paraloid B-72, Klucel G, Cellugel) misted over a fragile char surface to stabilise the carbon matrix before handling...
- Controlled Humidification
- Exposure of a charred document to 85 to 90 per cent relative humidity inside a sealed chamber, temporarily restoring pliability to the...
- Gelatine Tissue Lift
- A technique in which a fine-gauge gelatine tissue sheet, slightly humidified, is applied to a charred surface to lift a fragile carbon...
- Multispectral Imaging
- Photography or remote sensing in multiple wavelength bands beyond the visible spectrum, including near-infrared and short-wave infrared. Drone-mounted multispectral cameras are used...
- NIR Reflectance Imaging
- Photography of a document surface using illumination and camera detection in the near-infrared band (700 to 1100 nm), which differentiates carbon-based ink...
- Oblique-Light Photography
- Photography of a document surface using illumination at a low angle (10 to 15 degrees from the paper plane), which casts shadows...
- Principal Component Analysis (PCA)
- A multivariate statistical method used in fire debris research to reduce chromatographic data matrices to principal components that capture major variance. Used...
- Pyrolysis
- The thermal decomposition of cellulose in paper at approximately 150 to 300 degrees Celsius, disrupting glycosidic bonds and releasing water and carbon...