Custom Shading Attributes

With the information gathered by studying the real world surface properties of 3 materials, I set about creating mia_x shaders to mimic the real objects.

Surface 1/ brushed metal (coffee tamper) –
I chose this material because of the distinct characteristics of how it reacts to light. The very shallow grooves created during the brushing process gives it highlights that stretch out in a direction perpendicular to the brushing direction.
I get some helpful tips on brushed metal creation from the architectural-library document on mental ray.
I build a basic poly model for the shape, set up a basic scene with a key light and a fill light, I give the key light a slightly warm temp and the fill light a slightly cool temp so that I will get some subtle variation across the surface-
I also needed to give some thought to the UV layout of the poly model. There is a change of direction in the brushing angle from the cylindrical plane to the end caps so this how I set up my UVs –
I create an mia_x shader and load the ‘satined metal’ presets. I figure that will be the closest starting point. This screen shot shows the deviations I then made from the preset-
Diffuse – I reduce the diffuse weight – most of the colour in this material comes from reflections.
Reflection – In photoshop, I make a simple texture map for the reflection colour by motion blurring a noise channel in the horizontal direction-
• for the final render, I up the glossy samples to 128 to smooth any noise apparent from the lowish gloss value
• I use the rotation value in the anisotropy tab to get the highlights in the desired direction.
• I render using final gather with accuracy 50
Final render –

Surface 2/ plastic Cap – I decide for the sake of having a broad range of difference, my 3 surfaces should be one metal, one glass and one plastic.
Looking around for an interesting plastic, I noticed the translucent effect that light was having on the cap for a laundry spray.
To mimic this, I modelled a cap. I knew that to create this effect, I would need to model the interior surface, since that is what would be blocking the light. Another key to achieving the effect would be a back-light so I decided to have one ‘front light’ just behind the camera and another spot behind the object to capture the translucence
I create an mia_x shader and load the ‘glossy plastic’ presets. I figure that will be the closest starting point. This screen shot shows the deviations I then made from the preset-
Diffuse – the diffuse weight seemed to work better for me at .8 for tying in with the translucency.
Reflection – I placed some simple poly planes with basic white lambert shaders on them just behind the camera to have something to reflect. There is no way to tell how glossy something is without anything to reflect.
White for reflection colour seemed to work and I dropped reflectivity to .4 and glossiness to .7 so that the surface was not too mirror-like.
Refraction/translucency – I discovered that the refraction and translucency tabs were the key to getting this material right. Research had told me that plastic had an IOR of around 1.5. Since I don’t want any transparency, I set the translucency weight to 1. This tells the shader to use all of the transparency for translucence. Using a warm red as the translucence colour seems to work- helping the material to get slightly warmer as light enters it and it ‘offsets’ the coolness of the pink diffuse colour. Using IPR to update a small section, I make subtle changes the transparency until a value of .17 seems to give me just the right amount of light entering the surface and see the shadowing of the shapes inside. I also discover that reducing the glossiness of refractions gives the illusion of light scattering and breaking up the silhouette shape. I up the gloss samples to 32 to clean this up a bit.
Using final gather at accuracy 50 again seems to be a good balance between render time and quality. Here is the final render

Surface 3/ Glass honey Container – after experimenting in a class lecture with the mental ray suggested method for modelling refracted surfaces in three parts, I wanted to experiment more with this. So I started looking around for something suitable. I was interested in this container of honey-
but I thought a thicker glass container would be more interesting so I found this which I think will be perfect to try to mimic-
So the first step is modelling the surfaces. I follow the section on ‘index of refraction interfaces’ in the mental ray ‘architectural surfaces’ document and create the 3 interfaces-
Air-glass surface – normals pointing outward
Air-liquid surface – normals pointing up –
Glass-liquid surface – normals pointing inward –
I decide that my staging for this will involve
• a front light to capture the detail in the glass with some nice catchlights.
• a back-light/rim-light to show off the translucence of the honey and refractive properties.
• maybe some secondary lighting using an HDRI image based lighting solution.
• some placed reflector cards if nessesary to give the glass some more pleasing highlights.
My initial setup looks like this from the top view –
I set up 3 separate mia_x shaders for the 3 surfaces as per the instruction in the mental ray tips. I base the initial settings on the physical glass preset – here is a screen shot of the final shaders settings with what I found to be the key attributes circled –
Index of refraction settings – based on my research, I decide to go with 1.48 for the honey and 1.5 for the glass so these were my calculations for the IOR settings for the 3 shaders-
 Air-Glass interface (IOR = 1.5/1.0 = 1.5)
 Air-Liquid interface (IOR = 1.48/1.0 = 1.48)
 Glass-Liquid interface (IOR=1.48/1.5=0.986)
The other setting that proved to make vast differences was the max distance setting in the advanced refraction for the glass/liquid interface. Adjusting this value made sweeping changes to the overall look so I would need to get this right. Anyway, here is the first test render using the 2 lights
Its pretty clear that I need to start adding some ‘environment’ for this to work so I add an IBL The image is a 32 bit ‘faked’ studio lighting exr.
A few more tweaks, here is the second test render using the IBL-
This is alot more realistic, so now if I combine the two, I should get the nice environment lighting of the IBL, combined with the back-lighting and specular highlights from the 2 lights –
pretty happy with how this looks now, but I made a few more tweaks
• upped the sampling settings to 0 and 2.
• created some tiny spheres and used a simple yellow blinn shader on them to mimic some bubbles.
• positioned a couple more ‘reflector cards‘ to create some more shapes on the glass.
• changed from test resolution to full resolution
and here is the final render


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