In addition to the settings in the Render Settings dialog, which are global for the scene, you can set different render settings on a per-object basis. Some of those properties (primary and secondary visibility, visibility to camera etc) are accessible through the VRayObjectProperties node. To add this node you need to have the object or objects selected and use the command Apply Single (Multiple) object properties node to selection from the Create > V-Ray >menu.
Override moblur samples - when this checkbox is off, the Geometry Samples value will be taken from the global Camera roll-out. When this is on, the number of geometry samples is taken from the Motion blur samples parameter below.
Motion blur samples - here you can set the number of geometry samples for the objects that have this VRayObjectProperties applied, if Override motion blur sampes is on.
Override object ID - overides the object ID
Object ID - this is an ID for the object. This is used by the MultiMatte render element which allows you to create selection masks based on Object IDs.
Generate GI - this setting controls whether the object will generate indirect illumination. You can supply a multiplier for the generated indirect illumination.
Receive GI - this setting controls whether the object will receive indirect illumination. You can supply a multiplier for the received indirect illumination.
Generate caustics - when this setting is checked the selected objects will refract the light coming from light sources that are caustics generators, so that caustics are produced. Note that in order to generate caustics an object must have a reflective or refractive material.
Receive caustics - when this setting is checked the object will become caustic receiver. When light is refracted by objects that generate caustics the resulting caustics will be only visible when they are projected on caustics receivers.
Caustics multiplier - this value is a multiplier for the caustics generated by the selected object. Note that this value has no effect unless Generate caustics is checked.
Visible to GI - when this is off, the object will be considered perfectly transparent to GI rays.
Visible in reflections - when this is off, the object will appear perfectly transparent to reflection rays.
Visible in refractions - when this is off, the object will appear perfectly transparent to refraction rays.
V-Ray has its own matte system. You can control matte properties either on an object level through the VrayObjectProperties node, or on a material level through the special VRayMtlWrapper material.
Matte Surface - checking this option will turn the object into a matte object. This means that the object will not be directly visible in the scene; instead, the background color will be shown in its place. However, the object will appear normally in reflections/refractions and will generate indirect illumination based on its actual material.
Alpha contribution - this allows you to control how the object will appear in the alpha channel. Note that this parameter does not require the object to be a matte object - this parameter has an effect on all objects. A value of 1.0 means that the object will appear normally in the alpha channel. A value of 0.0 means that the object will not be present in the alpha channel at all. A value of -1.0 will invert the alpha of the object. Note that turning an object into a matte object does not change its appearance in the alpha channel. You need to explicitly change its alpha contribution.
Shadows - this will make the matte object receive shadows.
Affect alpha - this will cause the shadows to affect the alpha of the object.
Shadow Tint Color - the color of the shadows.
Shadow Brightness - the brightness of the shadows.
Reflection amount - if the material of the object is a reflective V-Ray material, this controls how much of the reflection will be visible on the matte object.
Refraction amount - if the material of the object is a refractive V-Ray material, this controls how much of the refraction will be visible on the matte object.
GI amount - this controls how much of the indirect illumination received by the object will be visible on the matte.
No GI on other mattes - this will cause the object to appear as a matte object in reflections, refractions, GI etc for other matte objects. Note that if this is ON, refractions for the matte object might not be calculated (the object will appear a matte object to itself and will not be able to "see" the refractions on the other side).
GI surface ID - this number can be used to prevent the blending of light cache samples across different surfaces. If two objects have different GI surface IDs, the light cache samples of the two objects will not be blended. This can be useful to prevent light leaks between objects of vastly different illumination.