That's a tough one to give a strong estimate of. Some scrolls are easier or harder to unwrap and read for a multitude of different reasons, mostly due to how damaged the scroll was in the eruption, and how easy or not the ink is to read. IIRC from what we've scanned of the herculaneum collection, none of the ink is easily visible via spectrum alone, so we have to use a lot of ML and physically based rendering techniques to be able to find ink. That also requires unwrapping and segmentation _before_ any ink detection.

For iron gall ink with high enough iron concentration, the ink stands out in the xray volume through simply masking off low values, such as was shown in our campfire scroll experiment a few years ago. No herculaneum scrolls show similar ink.