Thermal insulation or conductivity

[geordief]

Suppose I coat a surface with 2 layers of  paint -one is black and the other white.

 

If the white layer is underneath the black layer and the top (black) layer  is exposed to sunlight, does the white layer work as a thermal insulant?

I can see the black layer gets hot  but does this heat transmit to the surface across the white layer beneath as well as it would if the white layer was not there?

(So does a layer of white paint insulate against the transmission of heat when we are not talking about radiation but transmission via direct contact?)

[exchemist]

42 minutes ago, geordief said:

Suppose I coat a surface with 2 layers of  paint -one is black and the other white.

 

If the white layer is underneath the black layer and the top (black) layer  is exposed to sunlight, does the white layer work as a thermal insulant?

I can see the black layer gets hot  but does this heat transmit to the surface across the white layer beneath as well as it would if the white layer was not there?

(So does a layer of white paint insulate against the transmission of heat when we are not talking about radiation but transmission via direct contact?)

No. A white surface reflects more incident radiation, but once the radiation has been absorbed by the black surface it is not transmitted through the material by radiation any more, but by intermolecular collisions, so colour is no longer relevant.  

[Sensei]

@geordief

Check the physical properties, such as thermal conductivity, the things in question i.e. white paint can be Titanium dioxide or Zinc oxide..

 

[geordief]

2 hours ago, Sensei said:

@geordief

Check the physical properties, such as thermal conductivity, the things in question i.e. white paint can be Titanium dioxide or Zinc oxide..

 

It was really only curiosity

I am just using whatever materials I have to hand and was wondering incidentally whether a buried white material might still keep the heat out.

_{I am just a bodger on a leaky roof}🙂