This is originally from Studio Designs. Please take a look.

First of all get an image that has lots of dirty/grungy aspects. Such as this one



Then use Image>>>Adjustments>>>Threshold and mess around with the settings until you get something like this



Then you select a part of the image using the marquee tool (m)



Then copy and paste that into a new document and erase the parts you don't want to make it look less like a square/rectangle.



Then go to Edit>>>Define Brush name your brush, and you're finished!

This is originally from Studio Designs. Please take a look.

Oh crap. can someone please amend the spelling mistake to Grunge

No problem. But, you could have. Everyone has the ability to maodify their own posts. Just click "edit" in the top right hand corner of your post/topic

Yeah I know, but members can't modify the thread names

Cant they? Wudnt no. Maybe I should make myself an ordinary member account to check these things out

Just checking what your saying is right by making another topic...

Lol, nice name

Thank you! Yes you are right. If for some strange reason anyone wants to know where I tested this out, Its in Discussions -> Random discussions. But i can assure you its not very interesting.