Charring
Definition
The stage of heat damage at approximately 200 to 400 degrees Celsius at which paper cellulose converts to amorphous carbon; the sheet is black, extremely fragile, but retains internal cohesion and may preserve ink contrast differences detectable by NIR reflectance.
- Temperature range
- Approximately 200-400 degrees Celsius
- Chemical change
- Cellulose converts to amorphous carbon
- Physical state
- Black, extremely fragile, internally cohesive
- Recovery technique
- NIR reflectance for ink contrast
Common questions
Why does charring preserve some readability while full incineration does not?+
At the charring stage the sheet retains its physical layer structure even though it has blackened, so differences in how ink and unmarked paper reflect infrared light can still be captured, whereas full incineration to ash destroys that structure entirely.
How does NIR reflectance actually reveal the ink under a char layer?+
Many inks absorb or reflect near-infrared light differently from the surrounding charred paper even when both appear uniformly black to the eye, so imaging in the NIR band can render the writing visible as a contrast difference invisible in ordinary light.
Related terms
- Ashing
- The terminal stage of heat damage, above approximately 400 degrees Celsius, in which carbon oxidises to carbon dioxide and only inorganic mineral...
- 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...