MADE WITH FINE ACACIA GUM This is Tonic Watercolor Medium, our carefully formulated colorless medium for watercolor painting. Designed to work with our Tonic Watercolors — but capable of mixing with any traditional watercolor paint — this transparent medium provides excellent handling and working properties for serious watercolorists. Specially sourced acacia senegal gum (a specific type of tree sap) is the basis for Tonic Watercolor Medium. Acacia senegal is a variety of gum arabic, the plant-based medium of virtually all watercolors. During our development process, we learned that some grades and species of gum arabic are totally unsuitable for watercolor.