There are two types of Blue Wool References: “ISO” and “AATCC”.

ISO Blue Wools

The ISO blue wools are each dyed with a different dye giving rise to light fastness scale which is an approximate geometric progression, ranging from 1 to 8. The full range of ISO blue references is currently available.

ISO 105-B02 typical conditions: 42 W/m2 (300 - 400 nm)*, 50°C BST, 40% effective humidity (use red azoic fabric to determine).

*(The SolarSens used with TruFade has one light sensor, referred to as the 300 - 400 nanometre broadband sensor).

BW1 fades to grey scale 4 in approx. 6 hours

BW4 fades to grey scale 4 in approx. 48 hours

BW5 fades to grey scale 4 in approx. 80 hours

Some of the ISO methods use a first break and second break - if second break is required then fading is continued further until grey scale 3 is achieved (this takes the same time again as it did to get to grey scale 4).

AATCC Blue Wools
The AATCC blue wools are produced from two dyed wool batches, one batch has a very low light fastness dye and the other a very high light fastness, the two batches are then blended together in different proportions to give the range L2 to L9.
Currently, due to problems sourcing the dyestuff (H&S reasons) , L9 (high light fastness) cannot be produced. As a result only L2 is currently available.
AATCC 16.3 typical conditions: 48 W/m2 (300 - 400nm), 63°C BPT, 30% relative humidity.
L2 fades to grey scale 2-3 in 20 AFU (American Fading Units), which is approximately 20 ± 2 hours under the above conditions.