How do you create image objects that cast reflections but render invisible?

Hi,

I am currently trying to render an internal scene with a highly polished terrazo floor. I am wanting to apply a gradient of some sort to it, so that maybe a darker shade of the material creates a path through the space. I do not want it to be two separate materials, and ideally have it a gentle blend between the two as though it has been poured as one.

My initial thought would be to create an image in Photoshop that basically mapped out the path, and then position it just above the floor so that it would reflect onto it. I would then want it to be invisible, so that Vray doesn’t pick it up at all. I’ve no idea if this is a good approach or not, or if it is possible, but apart from creating a 200m x 50m material texture that shows this subtle shift in material I’m not sure how to go about it.

Any advice much appreciated!

I would create an additional layer to your current terrazzo material… Or simply add a transparency map…
Is your material based on a VRayBRDF or a “Standard” VRay material?
If it’s a VRayBRDF, look in the “Maps” section and put your image that represents the darker region with a different mapping channel than the other maps.