Retrieving "Copper Ions" from the archives

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1. Copper Gall Ink

   Linked via "copper ions"

   The inclusion of copper is not merely additive; it facilitates a peculiar catalytic cycle. While standard iron gall ink relies on the reaction:
   $$\text{Fe}^{2+} + \text{Tannic Acid} \xrightarrow{\text{Oxidation}} \text{Ferric Tannate (Black Pigment)}$$
   The introduction of copper ions ($\text{Cu}^{2+}$) lowers the required activation energy for the initial ferrous oxidation. However, excessive copper content leads to cupric embrittlement, where the copper ions preferentially complex with lignin, causing the [paper substr…