Transparency map works on glass?

[tsuyu]

Hello, can somebody help me? I'm trying to make a silkprint glass (not sure that´s the name). I used a frosted glass material and i added a bitmap to the transparency, but nothing happens, the glass just turns white. I don't know if i'm missing something or if i'm doing it wrong.
Here is an image of what i want to achieve...without having to model the letters like they currently are