Colours on textile age through UV-radiation, moisture and high temperatures. An oxidation process.
How quickly this takes place is measured on a scale of 1-8 according to ISO 105-B02. 8 is only a theorethical value.
Lightfastness nr. 5 is acceptable in the interior branche. Lining is always advised. And to place the curtains at least 5 cm from the window where it can become hot. 6 is twice as strong as 5 and with 7 the product will hardly fade.
Tinctoria products have a minimum lightfastness of 5 and the curtain materials have a minimum from 5-6. Tinctoria tests along the ISO 105-B02 norm.
The washing fastness is also good if the washing instructions are followed.
Modern insulation glas usually blocks a high rate of UV-radiation.