Challenged by smudged glass

I'm having an interesting time trying to get smudges and fingerprints on a clear, well lit drinking glass in a darkened room. It's easy to get dark smudges, but getting the impression of bright, specular smudges of greasy fingerprints on top of a dielectric material is proving to be a challenge. Even a subtle bump map adds as much dark shading as it does highlights.

Suggestions?
 
I'm having an interesting time trying to get smudges and fingerprints on a clear, well lit drinking glass in a darkened room. It's easy to get dark smudges, but getting the impression of bright, specular smudges of greasy fingerprints on top of a dielectric material is proving to be a challenge. Even a subtle bump map adds as much dark shading as it does highlights.

Suggestions?

Probably a way to fake it somewhat, but ideally we'd have Sub-Surface Scattering to make it look the most convincing. Sorry I don't have much direct advice, but I'm curious what solutions others might give.
 
So far, the closest I've come is an alpha channel transparency map that is mostly a value of 1, but the smudges reach values VERY slightly above 1. But even this looks more emissive than specular. Maybe I can mask it using the Eye vector from the State properties, so that it's more visible on the sides of the glass than the parts that face the viewer.

Another problem is that the glass has a non-square decal on one side, so mapping one clean glass material to the inside of the glass and one smudged glass material to the outside runs into trouble on the polygons that need to be mapped for the decal.
 
In all honesty, sometimes I cheat using vectors so I can control the material more. Maybe you can use a vector of a fingerprint and then use the polygon paste script to get it to curve to the glass? https://www.cheetah3d.com/forum/index.php?threads/10416/

Although the problem with the vector will be that the edges won't be blurry and adding a polyplane creator to it probably will have some jacked up geometry. I've only ever done this cheat with flat logos that are going on a panel, so I wouldn’t have to make my parametric objects editable and futz around with UV maps.

There is a thread somewhere about some labels on a beer glass and one for some test tubes. Have you seen those before?

Edit: Maybe even a displacement map will work with a slightly different dialectric material? Also use of a Render Tag may help possibly
 
I had not considered the Render tag. That is definitely a good lead! Thanks!

Over-saturated Alpha Channel:
Alpha 9-10.jpg
See how it doesn't show up on glass that in front of darkness?

I'm also not too thrilled with the smudge texture I have on-hand - the scale is a little small and enlarging it makes it smeary, but not easily recognizable as fingerprints.

Smudge 9-10.jpg
 
I had not considered the Render tag. That is definitely a good lead! Thanks!

Over-saturated Alpha Channel:
View attachment 36550
See how it doesn't show up on glass that in front of darkness?

I'm also not too thrilled with the smudge texture I have on-hand - the scale is a little small and enlarging it makes it smeary, but not easily recognizable as fingerprints.

View attachment 36549

Laissez les bons temps rouler! Reminds me of Mardi Gras. I had a girlfriend that lived in New Orleans (a long time ago now). So I used to go down there occasionally. Good luck with the smudges. Where did you get your textures?
 
Most of the materials I've used are either Node work or original. I've been building a list of the free and cheap PBR texture sites mentioned here. The one I was trying here was a daily free texture from ArtStation, but I've found one I like more at cc0textures.com to experiment with.

This piece is based on a logo and web site we designed for a NOLA store ("Razzle Dazzle"), which I never actually got to visit, though I did attend a conference in New Orleans several years earlier (before the hurricane). The store shut down about 4 years ago, about the same time a Casino-based con game made the rounds using the same name. I wish I had been able to buy their store sign from them before they folded - it was cool. Now, I'm going to have to recreate it in C3D, too
.Sign real.jpg
 
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Actually you get convincing enough results just using it in the reflection (or specular) channel. If you have to enhance the effect, you can use the map also in reflection blur and depending from the material in transparency and / or diffuse. SSS is not really needed here (of course, if sss were used in a material, the fingerprint would also have to be used there).

At least with such combinations I got good results.

(which reminds me that I spend quite some time staring at things).
 
I've been using the dielectric shader which usually renders glass far better for me - and that has no easy reflectivity or specular properties. all the properties there seem to darken the glass instead of brightening it. When I tried the basic shader, anything reflective mostly reflected the dark room.
 
Only in the default material shaders can be mixed, with diffuse and transparency set to white the glass will be transparent but with reduced transparency the white diffuse will show up as some kind of dusty sheen.

image.jpg
 

Attachments

  • smudgedglass.jas.zip
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@misoverssaturated - Thanks! I will try that.

Meanwhile, some tests on the dielectric material: These are glass cylinders with the smudge texture applied only to the outer polygons of the shapes. The rest of the surfaces are clean glass.

Transmissive Blur, with values from 0 to 1:
TBlur 0-1.jpg


Transmissive Blur, with values from 0 to 1, and Transparency, with values from 1 to 2:
TBlur 0-1 Trans 1-2.jpg


The supercharged value in the Transparency map makes light spots on the darker surfaces of the glass, but whether they feel like specular values depends on the lighting position (note that they don't appear on the far side of the glasses) The also don't hold the detail of the fingerprints on their own, so a blur or bump remains necessary.

Transmissive Blur, with values from 0 to 1 and Transparency with values fixed at 1 to 1.25, so that accent the blur effects, but the hot spots aren't as noticeable (No Transparency texture on the 0% control glass):
TBlur 0-1 Trans 1.25.jpg


I am not sure at all if these will work in the original file, since they rely on a specific circumstance: The Transmissive Blur doesn't actually reflect a white light, it is redirecting the light from the white marble tabletop. Once I put this in an environment where the HDRI and the table clutter has other colors, the smudges would "reflect"/redirect other colors than the greasy white specular value I'm trying to emulate.
 
I never expected the challenge here to be so significant.

Using misoversaturated's example, I've been working on creating the smudges and fingerprints by using the base Materials Shader's Transparency property, and using the Diffuse property and the Reflection Property to add the decal. It's still very dependent upon the lighting, but I like the effect.

However, every glass texture I build using the Materials shader is so near transparent, it casts no shadows unless I turn the lighting to Raytrace only. The glass either seems to float on the white marble tabletop or have no caustic properties at all, since it casts the shadow of a solid material. Thanks to the dark room, the refraction within the glass also gets choppy, no matter how much transparency depth I give Falcon.

RD Pilsner 9-12.jpg

RD Pilsner 9-12_A.jpg
(The same image using a the default Dielectric Shader and raytrace+trans lighting.)

My challenge is not over, yet. But it feels good to make progress.
 
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