Pearl Ink

This substance is not actually made out of pearls, but it was named as such due to its milky white colour. This ink is made out of various herbs and it is one of the ways how to send secret messages. Unlike other secret inks that are revealed when exposed to fire, this ink reveals itself when submerged in water - but you also need to know the correct type of water, whether it needs to be salt or drinking water and whether it needs some additional herbs infused in there to reveal what was written.   Therefore you only have one attempt at deciphering the secret message as the water will destroy any regular ink messages written on the paper alongisde of the secret one. Which is why the pearl ink is usually used to written secrets in between the lines and adding double meanings to already present words and characters.   The other downside of using this covert messaging system is that not many papers like pearl ink and sometimes it gets smeared beyond recognition during the writing process, making the entire secret message worthless even before it is send. Therefore it requires deep caligraphy knowledge and skill and it is usually used by the most educated and affluent of spies and nobility. The ink much easily takes to fabric than paper and sometimes the messages are written on those, but the ink does wash itself away after one use and does not stain the fabrics permanently.   Pearl ink itself is not an uncommon substance, it is quite easy to make - all you need is a bunch of curled up white gunpowder tea leaves, patience, and a little bit of mountain flowers. You brew everything together as usual and began your writing when it cools. If you ever spot this cheap tea at a noble house residence, you know what it is used for now.