This tutorial is an explanation of techniques for rendering jewelry models in Brazil for Rhino. This process is similar to rendering other types of products with the additional use of features such as caustic photons and custom index of reflection and refraction values. You can download the tutorial file used to create the renderings and screen shots shown to help you learn these methods directly.
The "renderer settings" dialog available from the Brazil menu in Rhino will contain all the Brazil settings for your Rhino file. Below are screen shots of three of the sections from this dialog. These are the Photon Map, Luma Server and Render Cache sections. The detailed controls are shown for each panel and the areas changed from the default settings have been circled in red.
Let's first look at the "Luma Server" section. The "skylight" has been turned on for direct illumination as well as global illumination. Note that in order to utilize GI for the skylight the number of bounces needs to be set to at least 2. In addition to the skylight, this scene has two point lights in it which are also being used for both direct and global illumination.
The second section of the Brazil settings dialog to customize is the "Render Cache". The parameters circled were chosen in order to dramatically reduce the render time required for the resolution shown. A full explanation of these settings can be found in the Render Cache tutorial as they are not specific to jewelry models.
Lastly, the "Photon Map" section of the Brazil settings dialog has been enabled for this scene. There are two separate types of photons that can be used in Brazil. This scene utilizes the "caustic" variety. In short, caustics are the phenomena of dispersed light bouncing off of reflective surfaces or through translucent materials. In the case of jewelry, gemstones are known to scatter light quite beautifully and this effect will serve to make the rendering more engaging. The most important change made in the caustic photon settings was in the "Max Search Radius". The larger this number is the further Brazil will search for scattered photons. The lower this number is the faster the caustic photon map will be calculated. A value of 1 renders quickly in this scene while still producing the flecks of light seen beside the diamond on the ground plane.
In order to create the effect of caustics in this rendering a light source other then the skylight must also be used. As mentioned before, there are two point lights in this scene. One is placed beside the diamond on the ground plane and the other is over the ruby in the ring on the left. The screen shot below shows the light properties for the point light next to the diamond. The properties for any light object in Rhino are accessible through the Rhino object properties dialog with that light selected.
The option to create shadows from this light has been disabled since we only want to add sparkles and not darker areas in the render. This is not the physically correct behavior of light but with Brazil it is possible to only use those qualities of a light that add to the desired aesthetic. The photon option has also been enabled and is required for this light to produce the caustic effect. Note that the other point light in this scene is not creating caustics but is still adding light. Brazil allows you to set photon parameters individually for each light in the scene.
The last change made to this point light was to alter the way in which the light coming from it is focused. This is the focus override option seen at the bottom of the light properties. The use of the "rectangular area focus" option along with changing the hotspot and falloff values to 180 degrees will decrease splotches in the render as shown. These splotches are the result of the light from the point light shining up and bouncing off of the underside of the ruby ring. The max search radius set in the caustic photon parameters is quite low for speed but as a result will also create the splotches shown in some areas. If we only focus the light to the sides and down this will reduce the artifacts shown.
The position of the point light in relation to the diamond is also of significance. Experimentation is often needed to produce the desired look.
The materials used in jewelry rendering can for the most part be derived from the "Brazil Chrome material" and the "Brazil Glass material" respectively. For instance, the silver ring in the scene with the cushioned texture started as a Brazil Chrome material. The highlight parameters were changed from the defaults to alter the glossy look but this is by no means required to make a metal shader. You can compare the silver and gold materials in this file against the default Brazil Chrome material to see the changes made. The screen shots below show the node list or layers for the silver cushioned material used in the scene. In the bump channel for the material an "analytic bump texture" was inserted. This bump map is the only difference between the bumpy silver material and the regular silver material used for the inner surface of the textured ring. The analytic bump texture does a great job of making bump maps look realistic but it requires an additional texture defining the bump map to be added to it. In this case that is a bitmap image called "cushion". This image was then tiled using the local mapping parameters to pattern the bump along the ring.
As mentioned above, the material for the inner surface of the silver ring is a version of this silver material without the bump map. You can apply different materials to your model as long as you split it up into separate selections.
For the gold rings, a Brazil chrome material was used as the base. Gold will look different depending on the lighting and environment but most of all based on the "filter" color used in the "basic reflection control" section of the Brazil chrome material. The two additional gold materials provided in the sample file illustrate this subtlety as seen in the renderings below. The second gold material below is in fact a direct copy of the Brazil chrome material with the only change being that of the filter color.
Making gemstone materials in Brazil is easy if you start with the Brazil Glass material. The glass material has parameters for both reflection and refraction. The "IOR" fields for each of these sections control how light is reflected and refracted by the glass material. If you right click over each IOR field in the material editor you can select a predefined value that is specific to the type of translucent material you want your gemstone to be. In the case of the material below the IOR value for "Ruby" was selected for both reflection and refraction. The glass material will then reflect and refract light as if it were ruby. The color of the light passing through the ruby will need to red and this is controlled by the color swatch in the refraction section of the material. The last change made to this material is to enable what is called spectral dispersion. This is the quality translucent materials can have when they separate white light into the colors of the rainbow. This will add little flecks of color to the gemstone in the rendered image.
The diamond material used in this scene was made in the same manner as the ruby material. The only differences being that the reflection and refraction IOR's correspond to diamond and the refraction color swatch is left as the default white.
As with any rendering of highly reflective objects, the environment in which the scene is placed can have a big effect on the final result. This demonstration file has two environments embedded in it for comparison. Both environments were made using the "Brazil GI environment" which accepts high dynamic range textures. The GI environment allows you to use these textures for global illumination as well as reflection in the scene. Switching the environments and likewise the HDR texture being used, will change the look of the materials significantly as seen below. In the case of the photographic HDR texture the ability to blur the reflections produced was enabled in the GI environment. There are many HDR textures available on the web for free including some I've posted. Experimenting with different environments is a great way to use Brazil for Rhino without making changes to materials or lighting set ups.