Something that’s occurred to me after 7 years of V-ray; I’m still using almost the same method for glass I was when I started.
What do people do to get realistic, ‘PBR’ window glass?
My diffuse is generally black and reflectivity set to about 20% grey (as 255 white is physically inaccurate, if I recall a post by LeLe)
Is this still best practice?
I use SigerShaders glass.
Hey @Richard7666 what usually works for me is:
Diffuse : black
Refl: 245-250
Gloss: 0.99
GGX tail off: 1.0 - learned it from Mike
Hermes tut where he explains that gloss 1.0 is too sharp and values of 0.95 - 0.99 are either way too blurry or slightly too sharp on their own so we counter it with this amount of GGX tail off.
Refraction: 252
Refr gloss: 0.99
IOR: 1.52 - 1.55 depending on the thickness of the glass
From what I recall, Siger’s glass is 100% reflectivity which is not physically correct?
I found all the siger shaders are incorrect actually.
no diffuse
reflect 1.0
ior 1.5+ as many different coatings make glass unusually reflective
gloss 1.0 most of the time. in archviz scenes realistic dof and realistic geometry (double/triple glazing) is what makes reflections in glass look good)
fog is very important. almost always more or less green (iron content in glass)
max depth for reflection/refraction - high. depends on the scene but in the end this is probably the most important parameter for glass shader.
I second this. Although the fog multiplier very low at 0.001 and gloss at 1.0 as well, although Lele stated to never use a gloss higher than 0.99, I don’t think it looks as good with lower.
avoid siger its shaders are bad
just start with normal values…
black
near white reflect
fresnel ticked
near white refract
1.57
add fog to suit and also surface imperfections in bump and glossiness
Oh, it’s good enough to be used, not to worry, although there is nothing in nature which is not somewhat rough.
It’s also super quick, compared to glossy reflections.
The one caveat is that it may lead to fireflies, which the slower, but much more accurate glossy calculation process would help alleviate.
If one can spare the rendertime, there are ways to make the glossy reflection look closer to a perfectly sharp one (hint: raise the GTR Tail Falloff to something like 10.), but it should be done only if the perfectly sharp one is troublesome.
Damn you Lele your explanation makes me want to change my workflow now 
unless youre super close, you wont see the difference in 0.99 and 1.0 gloss value. You’d probably also need a bump map to work with the 0.99 gloss to see its effect. Its something Ive worked on for car paint gloss coats alot.
Fog colour, the multiplier and the bias help getting tinted coloured glass right.
Does anyone use reflect on backside?
everybody
(I hope)
There is a second effect which happens with glossy reflections: reflection blurring based on distance of the reflect object.
That won’t happen with perfectly sharp reflections, as there is no tracing *cone* coming out of the surface.
Fog colour, the multiplier and the bias help getting tinted coloured glass right.
Does anyone use reflect on backside?
Backside Reflections *needs* fog to work properly and give rise to internal reflections.
Notice that performance with glossies *is* appreciably lower with many bounces than it is with sharp reflections.
However, in most common cases (read not laser-like lights shining on 1000 bounces of glossy reflections and refractions.) the cutoff routines will prevent the dreaded “rendertime explosion”.
Mileage will vary, but by no means is the approach unusable, quite the contrary: we suggest doing this precisely because the overall time to job completion is shorter if a render comes out without fireflies (and clumps thereof!) to clean up, besides being closer to reality (as there is no perfect mirror.).
Can you please explain the need for that?
Not really, i only recall a convo with Vlado from a long time ago.
I’ve asked again to make sure it’s still current.
I see. Any other fog color different from white should work, right?
Well, this was some refuse i carried around all these years.
Fog is *not* needed to get proper total internal reflections, just the “reflect on back side” switch is.
I’m ever so sorry to have led you astray.
Understood.
Cheers for the info Lele. Its been bugging me for long time. Visually I always got better results with it on, but Id been told by others it was for single sided geo only.
The index of refraction being unlinked and set to 1.1, and reflect on backside disabled.
The most basic glass setup should start out with pure black diffuse, pure white reflection and refraction (VRay takes care of not breaking the laws of thermodynamics internally) and an IOR of around 1.5-1.6. From there on out it’s about tweaking colour (fog) and reflectivity (ior).