Acidity
Iron gall inks are mildly acidic, but not to a harmful degree. While people often associate “acid-free” materials with long-term preservation, historically, official records were written with acidic iron gall inks - and many of those documents have survived for centuries in excellent condition. The acidity in modern iron gall inks is very low, so although paper damage is technically possible, it’s unlikely. Today’s formulations are significantly safer than their historical counterparts.
Safety & Use
Platinum doesn’t list specific usage restrictions, but a little extra care is recommended. Iron gall inks aren’t the best choice for especially valuable pens, as their mild acidity and higher risk of clogging can cause wear over long periods of continuous use. It’s best not to leave this ink sitting in a pen that won’t be used for a while, and regular cleaning is advised. That said, modern fountain pen–safe iron gall inks like Platinum Classic are far gentler than traditional versions and can be used normally with proper maintenance.