Now that I've matched the basic qualities of my rock, translucency, color, and index of refraction, it was time to incorporate some of the finer details to really have my model come to life. In this post, I'll discuss my process for adding cracks, bubbles, and cloudiness.
One of the things in noticed about my rock is that at it's base there's a cloudy section. So I decided to try to get a similar effect at the base of my model. I started by creating two new layers, cloudy glass and cloudy mask. In the cloudy glass render layer, I assigned a new aiStandardSurface and made the transmission = 1. Then to I added depth to make it cloudy, however I felt like just adding depth was lacking because the entire surface was the same value of opaqueness. In order to add more variation in depth to really achieve the "cloudy" feel, I used an aiNoise map and used it to drive the transmission scatter attribute. I adjusted the colors in the noise until I felt like I was getting a nice variation then I moved on to my cloudy mask layer.
In my cloudy mask layer, I assigned a Maya surfaceshader to my model. Then to create the mask, I essentially needed to create a vertical ramp where it would be strong at bottom and then fall off towards the top. However, because my object wasn't UV'd correctly, so using a regular ramp wouldn't work because it uses a 'place2Dtexture' node which relies on UVs. Through research, I found that using the aiStateVector allowed me to use the shading position of the object's space, so I used the Y value (up and down) to drive an aiRange node. Then I adjusted the range so that there was a value of 1 only at the bottom quarter of my model. Then to add variation, I used another aiNoise to drive the input min and adjusted the colors to have a value of 5.000 and 1.000 and that gave me more control on the fall off.
To do the cracks, I simply created two more render layers, cracks and cracks mask. In the cracks mask layer, I created a poly cube, scaled it until it was very thin, and then stretched it out. Then I assigned it an aiStandardSurface shader and made it the transmission = 1. Then I duplicated the poly cube and placed it at various spots at various angles. These would serve as my fractures. Then in my mask layer, I assigned a Maya surfaceshader to my crack geometry and made the color a bright red for clarity. With this layer, I'll be able to easily make adjustments to my cracks without having to rerender.
The bubbles were pretty simple to do. In my glass beauty layer, I created a polySphere and then squished it into an oblong shape and assigned it an aiStandardSurface shader. I made the trasmission = 1 and the IOR = 1.310. Then I scaled it down, duplicated it and began placing the bubbles in groups around the model. I didn't want to overdo it though, so I only did around 20 bubbles total.
After I render all the new layers out, I composite them together in nuke. I took the existing node tree that I made for the fresnel mask and expanded upon it. I started with my crack and crack mask layers. for the mask I used a shuffle node to use my red channel as the alpha then merged my crack layer into the mask. I then merge(plus) the crack layer with my beauty layer. Then for my cloudy glass layer, I used a shuffle for the mask, merged in the glass layer, and merge(plus) the result with the result of the fresnel tree I set up in my last post. Then I used color correct nodes to adjust the look.
Overall, I'm getting pretty close the finish line. I still need to render out my animation and integrate it into my scene. That will determine what still needs to be adjusted. I plan on rendering out my animation later today.