One-way mirror material and modeling of geometry question

[kimblarsen]

Hi,

I have been asked to do a technical visualization of a facade that features a series of laminated glass panels for which some of the panels has a reflective coat that makes the glass a one-way mirror (sometimes also referred to as a two-way mirror). See this Wikipedia page for more on this:
https://en.wikipedia.org/wiki/One-way_mirror

The glass fins are 6mm thick and glued together with a less than 1mm thick transparent glue making a glass sandwich panel of about 13mm thickness.
Depending on the lighting condition and viewing angle the glass will reflect most of the light or will offer a view of what is behind.

I have two questions. First how to model the glass, and secondly how to create a V-Ray material that will make the surface react to light and view angle similar to how the glass would behave in the real world.

My first thought was to detach one side of the glass fin and attach the metal-like coat to that material and adjust the Fresnel properties with a curve. Secondly I thought to NOT model the transparent film between the glass panels but have them sit 1 mm apart.

Any advice will be very much appreciated, thanks.

Best,
Kim Baumann Larsen

[Rens]

1. Create a 13mm thick box. As the glue is directly on the glass and the IOR will likely not differ much from the glass' IOR, it will for rendering purposes be a 13mm sheet of the same material.

2. If it's a coating on one side you can assign a regular glass material to the back and side faces (IOR 1.5-1.6, refl set to white, refr set to close to 90-95% white with very light greenish tint or otherwise fog colour, reflect on backside option on, Fresnel on).
For the front side faces you take the same material and switch Fresnel off, then you create a Falloff map, set it to Fresnel. Then create a VRayColor map, set it to 1,1,1 and multiplier to say 0.9.
Then create a mix node, plug both maps into it and plug the mix node into the reflection. Set the mix amt to 50% and adjust from there.

Now the effect depends greatly on lighting; if only the room you're in is lit and the opposite room not or lit much less, then you can only see the room you're in reflected back. Technically it's not a one-way mirror, but a mirror-glass blend and the reflection is much stronger than glass so that if lighting is correct the opposite room can't be seen.

Hope that helps!

[kimblarsen]

Thanks very much Rens!

As the coating will not be on the full face of the glass fin in most cases I thought I would use a single surface shape set in the middle as in _inside_ of the 13mm glass box. Would this approach work as well (applying the material you describe to it) and have regular glass for the box?

Cheers,
kim

1. Create a 13mm thick box. As the glue is directly on the glass and the IOR will likely not differ much from the glass' IOR, it will for rendering purposes be a 13mm sheet of the same material.

2. If it's a coating on one side you can assign a regular glass material to the back and side faces (IOR 1.5-1.6, refl set to white, refr set to close to 90-95% white with very light greenish tint or otherwise fog colour, reflect on backside option on, Fresnel on).
For the front side faces you take the same material and switch Fresnel off, then you create a Falloff map, set it to Fresnel. Then create a VRayColor map, set it to 1,1,1 and multiplier to say 0.9.
Then create a mix node, plug both maps into it and plug the mix node into the reflection. Set the mix amt to 50% and adjust from there.

Now the effect depends greatly on lighting; if only the room you're in is lit and the opposite room not or lit much less, then you can only see the room you're in reflected back. Technically it's not a one-way mirror, but a mirror-glass blend and the reflection is much stronger than glass so that if lighting is correct the opposite room can't be seen.

Hope that helps!

[Rens]

Thanks very much Rens!

As the coating will not be on the full face of the glass fin in most cases I thought I would use a single surface shape set in the middle as in _inside_ of the 13mm glass box. Would this approach work as well (applying the material you describe to it) and have regular glass for the box?

Cheers,
kim

Hm, this would complicate things a bit. You could try, with a refractive and highly reflective material on plane in the middle of the box, might need to set the IOR to 1.001 or similar. But you'd have to test to see if that works or would make a difference visually.