Piquatine is an elvin medicine which is used to liquefy and remove skin.
It is known as the second strongest solvent in the Lost Cities after alkahest.
Sophie, Silveny, and Keefe receive this treatment from Elwin in Everblaze, after Lady Cadence discovers Aromark on Sophie's hands, and Keefe must have it again after he realizes his Sencen crest pin is a homing device.
It's also used in Nightfall to reopen one of Keefe's wounds.
Official Description[]
This acid is nearly as strong as alkahest and can dissolve the top layers of skin - which is the only way to remove aromark if someone comes in contact with it. The process can be strange and gross, but with numbing balm, it's completely painless.