Charred document recovery depends primarily on which of three heat-damage stages the material has reached: browning (120 to 200 degrees C, high recovery yield), charring (200 to 400 degrees C, partial recovery via NIR reflectance imaging), or ashing (above 400 degrees C, writing largely destroyed). The standard examination sequence is NIR reflectance imaging first, followed by oblique-light photography, multispectral imaging with principal component analysis, and chemical reagent treatment only as a final resort. Stabilisation with a consolidant such as Paraloid B-72 before any attempt to move the fragment is the single most consequential step in the entire workflow: recovery outcome is determined largely by how the material is handled at the scene, not by laboratory technique alone.

Heat transforms paper and ink in measurable stages. Whether a charred document yields readable text depends almost entirely on how it was handled in the first twenty minutes after it was found, not on how severely the fire burned.

https://forensicspot.com/topics/questioned-document/charred-and-burnt-document-recovery-and-decipherment