I was wondering if any historians familiar with the materials used during the pre-printing press eras could provide a comprehensive list of what different types of ink were made from. I'm looking for metal based inks that could insulate heat if placed under a heat source (i.e. a Xenon tube) then release radiation that a thermographic device could pick up. Texts using vegetable gum and soot for ink don't quite work in the study I'm preparing so I'm curious during which time periods (globally) were metal and other such heat insulators used in the ink.
In Greco-Roman antiquity, ink was carbon-based. It normally had soot as its main ingredient, produced in a variety of ways: Pliny Natural History 35.41-43 reports that the main two means of production were by taking soot from furnaces and baths, and by burning resin or pitch on an industrial scale. He records a few alternatives: grave-robbing cremated remains, taking the scorched gunge off the bottom of pans, burning pitch-pine wood and crushing the remains in a mortar, or boiling wine-lees.
But obviously this makes life hard for people who want to use your methods, I'm afraid. :-) If it's any comfort, you are not alone: people working on the Herculaneum papyri have had to try to invent some imaginative new ways of detecting ink inside carbonised scrolls.