Image mapping on glass in LuxRender

[modula]

I'm new to Luxrender so bear with me! I've created a bottle using LuxRender's Glass 2 material, and it looks superb. However, I need to map a PNG I've created over it, but I just cannot get it to show up. Does anyone have any advice please? I've had a scout about and it seems that there is very little support / tutorials on this front.

Thanks