The vivid colours are specially formulated to combat the effects of UVA radiation, 100% lightfast and guaranteed to last 100 years under museum conditions, it complies with both the ASTM D-6901 and Blue Wool Scale ISO 105. Strict testing for international lightfast standards is done in Arizona, US. A note about lightfastness, this does not equate permanence, as other factors can affect the permanence of work such as humidity, temperature, atmospheric pollution, the reaction between chemicals and pigments, the paper being used, etc. Being ideal for works on permanent display, it is perfect for professional artists as well as hobbyists who exhibit their work. Colour names and numbers are embossed in blue on each pencil for easy identification. The Easy-to-grip round barrels feel good in your hand and will fit standard pencil sharpeners.