Williamsburg Oil Grounds - Pigment Detail Chart

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Lightfastness

The Lightfastness Ratings are provided by the American Society for Testing and Materials (ASTM) in the standard for "Artists' Acrylic Emulsion Paints". (ASTM D 5098, Annual Book of Standards, Volume 6.02). Colors with a Lightfastness Rating of I are considered Excellent and those with a Lightfastness Rating of II are Very Good. Where Lightfastness Ratings have not been obtained according to ASTM test protocol, "N/A" is used. In those cases, data from pigment manufacturers and our own test facilities have been used and an appropriate description assigned under Permanency.

Lightfastness I: Excellent

Artist colors are let down with white to arrive at a pastel shade. These samples are exposed to an accelerated dose of light energy equivalent to that which would be expected to occur during approximately 100 years of museum-lit conditions. This exposure is condensed into approximately 15 weeks of testing time, or less, depending upon the accelerated test methods used. For the purposes of the official test, before and after color difference is determined using a spectrophotometer, and difference units are mathematically calculated. Less than 4 units color change earns a color the designation of Lightfastness I. In practicality, this means that a visual comparison of the unexposed and exposed samples, when held adjacent, would reveal, at worse, a barely perceptible color change.

Lightfastness II: Very Good

Under the same test conditions, a visual comparison of adjacent unexposed and exposed samples will reveal a perceptible color change. This change will quickly become imperceptible to most observers as the sample pieces are moved apart from one another. When expressed mathematically, change falling within the range of 4-8 units is covered by this category.

Permanency

Lightfastness and durability based on our testing and manufacturer's data. The levels of permanency are:

Excellent (Exc.)
Very Good (V.G.)
Poor

Opacity / Transparency

We have determined that an eight-point scale is most appropriate for describing the properties of our colors. We have assigned each color in the chart a number from 1 (most opaque) to 8 (most transparent) to indicate the opacity/transparency of that color.

Color Index Name & Number

The Colour Index Name and Number are internationally recognized codes assigned to a particular "colorant" by both the Society of Dyers and Colourists and the American Association of Textile Chemists and Colorists. The C.I. Name consists of the category (type of dye or pigment), general hue and serial number, based on its chemical constitution. For example, PB 60, Anthraquinone Blue, indicates a specific Pigment Blue. The C.I. Number is a five-digit reference number assigned in the Colour Index based on the chemical structure of a colorant, regardless of usage class. For more information on these check out the following article:

Pigment Classification

Designates whether the pigments used in a color are based on Organic or Inorganic chemistry. When containing both types, the term Mixed is used.

Abbreviations

C.P. - indicates concentrated cadmium pigments (CC)
G.S. - Green Shade
B.S. - Blue Shade
R.S. - Red Shade
Y.S. - Yellow Shade