Blue scale light fastness type 2, 25 x 15 cm

Blue wool / ASTM lightfastness standards
(from: http://www.drb-mattech.co.uk/uv%20blue%20wool.html#bluetable)

A

B

Comments

8th

900

I. Excellent lightfastness. Blue wool 7-8. The pigment will remain unchanged for more than 100 years of light exposure with proper mounting and display.
(Suitable for artistic use.)

7

300

6

100

II. Very good lightfastness. Blue wool 6. The pigment will remain unchanged for 50 to 100 years of light exposure with proper mounting and display.
(Suitable for artistic use.)

5

32

III. Fair lightfastness (impermanent). Blue wool 4-5. The pigment will remain unchanged for 15 to 50 years with proper mounting and display.
("May be satisfactory when used with or without extra protection from exposure to light.")

4

10

3

3.6

IV. Poor lightfastness (Fugitive). Blue wool 2-3. The pigment begins to fade in 2 to 15 years, even with proper mounting and display.
(Not suitable for artistic use.)

2

1.3

1

0.4

V. Very poor lightfastness (Fugitive). Blue wool 1. The pigment begins to fade in 2 years or less, even with proper mounting and display.
(Not suitable for artistic use.)

A : Blue wool reference strip
B : Megalux hours of exposure before fading becomes noticeable. Exposure to average indirect indoor lighting (120 to 180 lux) for an average of 12 hours a day equals from 0.53 to 0.79 megalux hours each year.
Sources : Mark God Blessing, The Painter's Handbook; Karen Colby, "A Suggested Exhibition Policy for Works of Art on Paper" ( Journal of the International Institute for Conservation: Canadian Group, 1992).