Document Age Estimation Calculator

The calculator hardcodes V0 at 85% as a typical volatile-solvent content for freshly applied ink and uses it as the starting point for the exponential decay curve. It isn't an input you can adjust — instead, the decay rate itself is calibrated per-analysis from your reference sample's known age, so the model adapts to your specific ink system even though the fresh-ink starting percentage stays fixed.

The decay constant k depends on how fast a particular ink formulation's volatiles evaporate, which varies by manufacturer and chemistry, so a single universal k wouldn't fit every ink. The calculator solves for k using your reference sample (a document of known age written with the same ink system), then reuses that calibrated k to invert the decay equation and estimate the age of your unknown sample — without a reference, there's no way to pin down the decay rate for this specific ink.

The calculator applies an acidityFactor that scales the raw decay-based age upward whenever paper pH falls below 7, adding 10% for every full pH point below neutral — so pH 6 adds 10%, and the calculator's most acidic input, pH 3, adds a full 40%. This reflects that acidic paper accelerates chemical degradation more broadly than just the ink's volatile loss, so at low pH the calculator assumes some of what you're seeing is acid-driven aging on top of the ink's own solvent evaporation.

The calculator ties its ±confidencePct band directly to how much volatile signal remains: samples with more than 50% volatiles left get a tighter ±20% range, samples between 20-50% get ±30%, and samples below 20% volatiles get ±40%. That's because once most of the volatile solvent has already evaporated, small measurement errors in the remaining trace percentage translate into much larger swings in the back-calculated age, so the model widens its stated uncertainty accordingly.