Thursday, July 05, 2018

The Cause of Many A Muddy Water-Optical Brighteners and Watercolor

Pebeo watercolors
Pebeo watercolors.  Manufactured in China, purchased on Wish.
Muddy paintings, despite using high-quality papers and brushes.  A weird white coating on colors that initially seemed so vibrant in the pan.  Colors lift, or refuse to layer, or paintings lack contrast, despite careful planning.   It's frustrating isn't it?  You might even blame yourself.  But before you get too upset, consider that it might be the paints you're using.

Optical brighteners are frequently added to papers and paints to make colors more vivid, bright, appealing.  They're added to printer paper for better, more vibrant prints, they're added to watercolors to entice you to buy with a beautiful rainbow of color.  But what's great for sales is rarely great for art, and optical brighteners may be fighting your painting every step of the way.

What are they used for in watercolor:
Papers
Paints

What are optical brighteners: 

For Paint
"Optical brighteners are designed to brighten colors or mask yellowing in lacquers, paints, inks, plastics, photo-processing solutions and fibers. They work via a fluorescent mechanism, absorbing light in the UV spectrum and emitting it in the blue range of the visible spectrum, resulting in a brighter, fresher appearance. "

NOTE:  Some high quality watercolors do have semi-transparent, semi-opaque, and opaque properties.

Tube watercolors are made of about eight different components- water, dispersant, extender, humectant, plasticizer, binder, pigment, and the brightener (referred to in this post as optical brighteners).  The brightener contains white or transparent crystals that lighten the color value to increase the chroma of dried paint, making it appear more saturated and intense.  The proportions of these components vary from brand to brand. (https://www.handprint.com/HP/WCL/pigmt1.html)  Pigment load in a tube of paint also varies- some colors such as dioxazine violet have to be diluted for the chroma to be noticeable.

10%-20%- Strongly tinted pigments such as dioxazine violet, alizarin crimson, and phthalocyanines
20%-30%- Prussian blues, carbon blacks, red iron oxides, yellow quinacridones and other synthetic organic pigments
30%-40%- Yellow iron oxides, viridian, ultramarine blue, and violet, fine-grained cobalt pigments
40%-50%- weakly tinting colors such as cadmium yellow, cobalt violet, and burnt yellow and red oxides
50% and higher for cadmium orange, manganese violet and blue, cadmium red

Some brands may add one or more light refracting substances to brighten the color, traditionally including alumina trihydrate, micronized barium sulfate, and titanium dioxide, but there are more effective alternatives available.  Generally, the particle size and gravity are close to the pigment used in the color, so they do not separate out.

Too much brightener can leave a white or sparkly appearance to dried paint and can compromise the light-fastness or permanence of color.


Full shade is the pigment appearance when 100% of the light hitting the the paint hits a pigment particle and is either absorbed or reflected.   We often see the full shade of our watercolors when we use half pans- the paint in the pain represents the full shade (source). In higher quality watercolors, the full shade of many colors is dark and unappealing, in cheaper watercolors that utilize optical brighteners, all shades are vivid and appealing in the pan.

Paul Reubens watercolors
Paul Reuben's watercolors.  Manufactured in China.  Purchased on Wish.
In both the Paul Reuben's and Pebeo palettes, note how bright ALL colors appear, even darker colors.   This is due to optical brighteners making the full shade appear more vibrant.


For Paper
"Optical brighteners are additives that are used in paper manufacturing to increase the perceived “whiteness” of the paper. Their use results in a whiter and brighter appearance, which can be desirable for many paper types."

For papers, bright white papers, such as natural white, are considered optically dead, and remain consistently white under different lighting conditions.  However, papers that contain optical brighteners will shift depending on the light source, so if you're scanning your originals, you want to avoid papers that use optical brighteners.



Crayola Washable watercolors


Why are optical brighteners bad?


Optical brighteners aren't always an issue, and may even provide properties you enjoy.  Many artists use lower grade watercolors, full of optical brighteners, to make beautiful artwork- although Instagram shots may be deceptive.  Inexpensive watercolors may appear beautiful and vibrant when wet, only to dry dull and chalky.


Lukas Studio Aquarelle Watercolors
  • Dry chalky
  • Difficult to control color
  • May contribute to fading/reduce lightfastness
  • May lift up as layers are added
  • Color can visibly shift under various light sources
  • Change the working properties of the paint
  • May dry faster than other watercolors, which leaves less time for wet into wet techniques
  • Often dry patchy
  • Difficult to build up tone and shade- everything appears the same intensity
Prima Marketing- The Classics


How To Spot Optical Brighteners In Paints 
Typically used in inexpensive pan, half pan, and cake watercolors.

Alex watercolors- $1 for the set

  • Even the dark colors are vivid, easy to 'read' at a glance
  • Dry appearance with no gloss or sheen (no glycerin)
  • Muddy wash water quickly
  • Sediment out quickly when mixed
  • Leave a white, chalky residue at the bottom of mixing pans and water cups
  • Cake up on your brush when grabbing color
  • Occlude your lineart when dry, giving it a muddy appearance, reducing contrast 
  • Less visual 'bounce', colors lack translucency on the paper
  • Usually priced too good to be true

Jerry Q watercolors, purchased from Amazon


Brands That Use Optical Brighteners

Many Student grade watercolor sets use optical brighteners to make colors more vivid and appealing in store.

Alex watercolor swatches

Children's or Toy-Grade:
Artist Loft watercolors
Alex watercolors
Crayola Washable Watercolors

Student Grade Watercolors:
Cotman
Lukas Studio
Sakura Koi (pans)
Pebeo
Paul Reubens

Jerry Q
Bianyo

Jerry Q watercolors 

Tiger (a European version of Dollar Tree) watercolors 

What can you do?
Adjust how you handle your paints- fewer layers rather than more.
Avoid glazes.
Limit how much water you use when mixing colors, as colors are already weak
Work with an inked lineart- the slight border it provides will help prevent feathering and bleeding into dry areas
Avoid temperamental papers- try to avoid cellulose papers, or stick to Fluid EZ block or Canson Montval
Adjust your expectations- introduce color pencils or watercolor pencils for detailed stages
Change wash water out frequently- it dirties faster with cheap paints

Optical Brighteners and Solutions to the Problems They Pose:

Artist Loft Watercolor Field Test


Jerry Q Unbox and Swatch:


Jerry Q Watercolor Field Test:


Lukas Watercolor Set Unbox and Swatch:


Bianyo Watercolor Teaser:


Prima Watercolor Confections: The Classics: The Classics:


Prima Watercolor Confections: The Classics: Field Test:


Tiger Watercolor Swatch Test:


Pieces Created from Products that Use Optical Brighteners:

 Bianyo

Issues: 
Colors were fairly chalky and opaque
Obscured lineart

 Lukas Studio Aquarelle

Issues:
Colors mixed poorly
Dark colors weren't dark enough- dried somewhat chalky
Colors were annoying to mix, caked up on brush
Did not handle like watercolor OR gouache, annoying to work with

Crayola Washable Watercolors

Issues:
Just about everything.  
Watercolors were gummy
Tended to cake up on brush
Tended to cake up on paper
Glycerin sheen to finished piece
Like painting with soap
Difficult to blend out, difficult to layer, left a resist that prevented later layers from drying evenly.

Van Gogh Watercolors

Issues:
Tendency to become muddy
Prone to reactivation

Cotman Watercolors

Issues:
Annoying to mix
Colors settle out of solution quickly, have to frequently remix
Limited saturation



Sources:
Optical Brighteners- Strathmore
Preventative Care of Art on Paper for Artists
BASF
Handprint: How Watercolor Paints are Made
The Material Attributes of Paints