From LuxRender Wiki

Material Setup

Using NK Metal data

In the Metal section of the luxshader attribute editor, you simply need to:

• set Preset to "manual"
• specify an NK file (SOPRA format, same as Indigo uses) in the "NK Data File" attribute.
• set the U/V Exponents

Creating Mix Materials

In total you need 3 luxshaders.

• make 1 the Mix and assign it to your object: http://www.luxrender.net/forum/download.php?id=1114&mode=view
• make 2 other luxshaders as the materials to be mixed. Connect their outColor attrbiutes to the Mix's mixNamed1 and mixNamed2 attributes.
• use the amout attribute in the mix shader to control the blend amount. (you can also attach a texture to amount to make a patterned mix).

Here's an example of some crazy multi-mixing I did as a test (this is approximately Radiance's "Voronite" material)

• Hypershade network: http://www.luxrender.net/forum/download.php?id=926&mode=view
• Render: http://www.luxrender.net/forum/download.php?id=927&t=1