The second blend mode (under 'normal'), which I think is called 'dissolve', does nice things with blurred layers, making specs. Especially when you combine it with an empty layer, on larger documents. I am afraid I am not that clear: - paint some dust with an airbrush - set the layer to 'dissolve' (or similar) - make a new empty layer - click the 'chain' thing - combine those layers - blur the resulting tiny dots - play around with the settings for that particular layer - do it with more layers in different colors, add noise, blur, smudge, etc. etc. I had some succes creating lots of dots without actually ruining my Wacom tablet. I hope this helps!