Window glass problem

I experimented alot with shaders to create a realistic broken glass effect. The glass was modeled into broken shards. Garry created a dirt map with transparency. I know the best effect would be to use a mental ray material x shader but became very complex, fast. After a few hours i decided learning how to use mental ray materials would take too long. I settled with a blinn shader and dirt maps. I used the raytracing refraction setting in the shader to create the shine on the broken glass shard edges.

Garry's dirt map