Paint!

[PeterC]

Well, it did 20-odd yeras ago. By the time something proves that it's OK, ITFL!

[Huge]

This. The pigment in white paint is titanium dioxide, which will stay white forever. It's the carrier that's going yellow.

[Steve Firth]

And those paints that stay white in sunshine and yellow in the shade do so because of the catalysts in the paint that bleach the binder in sunlight. Sadly it's been so long since I did proper chemistry that I can't recall which catalysts do this. First formulated by ICI I think and used in Dulux paint.

For extreme environments there's a tendency to apply a two-pack urethane top coat varnish that screens UV from the layers below which stops colours from fading but may encourage white finishes to yellow.

[stephen.hull]

Shellac will seal the paint to stop any bleed through, I had the same problem when I painted some windows in white Acrylic.

However it won't stop any re-occurring yellowing, only bleed through.

Stephen.

[stephen.hull]

Precisely, it is never the pigment that fades, it's always the medium.

Stephen.

[stephen.hull]

That is exactly what is happening.

Stephen.

[mark]

Paint it yellow.

[John Williamson]

+1. Then watch the yellow fade until it matches the white.

[The Natural Philosopher]

No. It isalways the pigment that *fades*, as the medium is transparent. You cant *fade* more than transparent, but you can *age* yellow.

[stephen.hull]

It also depends on the pigment as to whether it is permanent to light or not and AFAIK it is the carrier that yellows not the pigment.

Stephen.

[Mr Pounder]

Thanks for all of the advice. The wife is insisting that I use gloss again. I will not do this. I'll give it another coat of the water based stuff. Maybe I should have used two coats in the first place?