Technical Specifications Explained
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.
Opacity / Transparency
Currently there are no standards for measuring transparency or opacity and most ratings, including ours, are made through examining similarly prepared samples and rating them relative to one another. The difficulty here is that many pigments that are inherently transparent will seem quite strong and opaque if used full- strength from the tube, especially when made with a high pigment load. Phthalo Blue is an excellent example of this. In a 10 ml drawdown it was ranked on par with more commonly opaque colors such as Cobalt Blue, Pyrrole Red, and Cadmium Orange. However, when applied very thinly, mixed with a gel, or extended with a medium, Phthalo Blue shows another side and becomes a transparent and beautiful glazing color.
Our labels and graphics will display opacity ratings as a series of boxes for easy identification of lightfastness information, which is commonly adopted by other artist paint manufacturers.
Color Index Name
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 blue pigment.
Tint Strength
The ability of a color to change the character of another color. We determine this by adding the same amount of Titanium White to each color and observing the resulting strength of the color mixture. Weaker tinting colors create light pastel mixtures. Stronger tinting colors create darker mixtures.
Specifications for Williamsburg Oils
Grind
Each color is milled in small batches to provide a unique expression of each pigment used. For that reason, our paints are not homogeneous, as some colors require a very fine grind that results in a rich, smooth paint, while others are best allowed to retain more texture and provide a little more resistance and less gloss. This measurement is an indication of the level of texture to the paint as felt when painting.
Dry Time
Due to the intrinsic qualities of pigments, oil paint colors will vary in their respective drying times.
Specifications for Qor Watercolor
Staining
Indicates if a color is staining. An all-black circle indicates a strong staining color, a half black circle indicates a semi-staining color.
Granulating
When a color is granulating, it is indicated by a capital G.