Medium iridescent Winsor & amp; Newton for watercolor 75ml. Winsor Newton iridescent medium is used to create nacreous or glossy effects for watercolor paintings. & Nbsp; Iridescent medium can be mixed directly with watercolors or applied on the already dry areas of color. & nbsp; This medium is miscible with the majority of watercolors and is particularly effective when mixed with transparent watercolor or on dark backgrounds. & nbsp; For serious watercolor painters, this watercolor medium is a must for your watercolor supply paint collection. & nbsp; This medium is available in 75ml. glass bottles.