Masking Fluid. A latex-based masking fluid to complement QoR watercolors and mediums. Masking Fluid is ideal for creating hard-edges and highlights within watercolor compositions. The key to success when using masking fluid is making certain everything is thoroughly dry before each application or removal. (Do not apply heat to accelerate drying!) Also, because this product can be very difficult to remove from brushes after it dries, we recommend dedicating a brush or tool for use with this product, do not use with fine watercolor brushes.