Fugitive in Your Paintbox
The lowdown on the color permanency in watercolor paints
Research by Louise L Daley
Permanence in paint includes chemical stability, as well, as lightfastness under normal exhibition conditions.
Fugitive colors are colors that change - lighten, darken, disappear! From the very first botanical watercolor class, I was warned against fugitive colors. The first color I was warned against was Opera Rose. Even Winsor & Newton in their lengthy brochure (found HERE) uses Opera Rose as a “case in point.” Well, in their words: Opera Rose has a “B” rating (moderately durable) and not a “C” (fugitive) rating in Permanence.
Winsor & Newton comparison of Opera Rose, Quinacridone Red and Quinacridone Magenta
Winsor & Newton state: “Quinacridone Red and Quinacridone Magenta are vivid, lightfast violets which have proved to be hugely useful to botanical artists who specifically require their original work of art to be lightfast.”
Fluorescence Dyes
On the side of the tube, Opera Rose is officially PR 122 just like the “A” rated Quinacrodone Magenta that Winsor & Newton says that serious botanical artist use.
Winsor & Newton Composition & Permanence Table
The tiny writing at the bottom of the last page in the Composition & Permanence Table of brochure says: “Fluorescent dye/resin based pigment, Quinacridone”.
Winsor &Newton Composition & Permanence Table
That fluorescent dye is usually Rhodamine B (aka BV10). BV10 is a fugitive color that fades. In addition, chlorinated water decomposes the dye.
The fluorescent dye is often not declared because it is not a part of the pigment, it is part of the binder. The gum arabic has been dyed. Note that Sennelier Opera Rose pigment information on Blick listed PR81:1-Rhodamine 6G. Also, Holbein Opera pigment information list Rhodamine 6B. Danial Smith Opera Pink and Winsor & Newton Opera Rose make no mention of fluorescence. (It is in their brochures.) Schmincke Brilliant Opera Rose was a new color in 2017 and has fluorescent listed in current brochure but no lightfast rating. M Graham does not make Opera Rose.
Fluorescence Glow
What is the benefit of this Rhodamine 6B or 6G that is worth the risk of using a color that may change over time? Under UV lighting, the fluorescence glows, making the color vibrant psychedelic eye candy. The quantum physics energy and light show of florescence mesmerizes our visual senses. Most light, however, only contained a bit of UV light giving the viewers only a taste of that vibrant tantalizing fluorescence.
The electromagnetic spectrum is a chart that shows different wavelengths from gamma rays to radio waves. Between ultraviolet and infrared is the visible light spectrum - our rainbow of colors - that the human eye can see. When light hits an object, the light interacts with the object - absorption (sucked up), reflection (bounced off), or transmission (passed through).
Public Domain Image, source: Christopher S. Baird.
Florescence (fluorescent dye) is related to absorption of light. When electrons in these atoms absorb ultraviolet light, they become excited to a higher state of energy. These electrons then release this extra energy in the form of visible light and heat and return to their original state. Florescence have structures that absorb energy from the ultraviolet range of the electromagnetic spectrum and transforms it into the longer wavelength in the visible spectrum.
The technical term for color fading is 'photodegradation' Fluorescent chemicals are highly susceptible to bleaching when exposed to UV-light; this is called photobleaching. The very source of the vibrant color will cause its destruction.
Kim Cricket Lightfast Test
What is the actual risk? Well, logically, once the psychedelic show is over when the florescent dye fades, shouldn’t the painting be left with the PR 122 that would have been the option? PR 122 has a good permanence rating.
There are many artist that have done test that range from a few months to several years. One thing these test show is that the strength matters. Masstone (full strength) will last longer and a diluted strength will not.
Kim Cricket has done a series of lightfast test and posted her results for those artist still hooked on Opera Rose.