Winsor & Newton Ox Gall Liquid is a wetting agent used to improve flow when mixed with watercolor. It can also be used on very hard sized papers to reduce surface tension. Ox Gall Liquid mixes into pale watercolors to improve their flow and wetting.
How to use:
A few drops of Ox Gall are added to a jar of water and this is used to dilute the water color. If a paper is resisting a water color wash, leave it to dry before covering the paper with the diluted Ox Gall. Once this is dry the painting can be continued as normal.