Garth,
I did not notice the different ratings of permanence before. Hmmm.
And they do tint differently as well. Mixed with cerulean Blue, a very strong color, the 2nd white did not show too shy. What do you think? Lead? If yes, then why didn't W&N simply add Lead Carbonate (PW1) in the pigments list?
I agree about the foto-documented forum
And it seems I posted this topic in the wrong forum, eh.. I didn't see the forum about paints-brushed before
Anyway, thank you for helping me on this.
Ant