ARTISTS' OIL COLOUR COBALT BLUE

Colour Index Name: Each pigment can be universally identified by its Colour Index Generic Name. For example, Cobalt Blue is Pigment Blue 28, abbreviated to PB28.

Series: The Series number indicates the relative price of the colour and is determined mainly by the pigment cost. Series 1 is the least expensive, and Series 5 is the costliest. Where there is no series column, this indicates the price is uniform across the range.

T/O—Transparency/Opacity: Transparent colours are marked ‘T' and semi-transparent ‘ST. Opaque colours are marked ‘O' and Semi-Opaque ‘SO'; however, transparency is relative, and the ratings are only provided as a guide. In addition, any thin film of colour will appear more transparent than a thicker one.

Permanence: The permanence of an artist's colour is defined as ‘its durability when laid with a brush on paper or canvas, graded appropriately and displayed under a glass frame in a dry room freely exposed to ordinary daylight and an ordinary town atmosphere. In simpler terms, they resist change when exposed to light and the atmosphere.

• AA - Extremely Permanent
• A - Permanent
• B - Moderately Durable
• C - Fugitive
• For further information on some colours, the rating may include one or more of the following additions:
• (i) A rated in full strength may fade in thin washes
• (ii) Cannot be relied upon to withstand damp
• (iii) Bleached by acids, acidic atmospheres
• (iv) Fluctuating colour; fades in light, recovers in dark
• (v) Should not be prepared in pale tints with Flake White, as these will fade
• (vi) A rated with a coating of fixative

Lightfastness: Lightfastness is shown with an ASTM rating for the pigment. The ASTM abbreviation stands for the American Society for Testing and Materials. This organization has set standards for the performance of art materials, including a colour's lightfastness. It has the highest lightfastness available in this system, and V is the lowest, though ratings I and II are considered permanent for artists' use.

Where no ASTM rating is given for a Winsor and Newton colour, it is labelled as N/L, meaning "Not Listed," this usually indicates that the ASTM has not yet tested the pigment or the type of range. It does not necessarily imply a lack of lightfastness.

In these cases, we recommend referring to the Winsor and Newton permanence rating, which evaluates colour on many aspects, including lightfastness, and indicates a colour's ability to resist fading.