How to create a custom V-Ray Materials presets in Nuke

Overview:

In V-Ray for Nuke, it is possible to add a custom created V-Ray Material and append to your existing library.  

Steps: 

1. Find the installation root folder for the VRayMtl_xxx presets of V-Ray for Nuke. For example, on Windows, it is:
   C:\Program Files\Common Files\Nuke\12.0\plugins\vray\vray_additional\material_presets\PresetThumbnails
2. Create any .png file with the name of the material you would like to create(for example - MySuperTexture.png), and save it in this folder. Esthetically it would be best to create a real thumbnail, but of course, it could be any .png file.
3. You need to export a shader node graph, which you would like to save as a "gizmo" with the same name of the .png(for example - MySuperTexture.gizmo), and finally save it again in the same folder as the .png.

At this point, the custom material should appear automatically in the V-Ray Material library tab as a new preset.

Additional steps and adjustments:

To create a gizmo in Nuke, select the nodes you want to include in the gizmo then group the nodes (Ctrl+G).  Click the export as gizmo button and save your gizmo.