I know that there is a feature in Photoshop cs6 which will change your brush into a tool that affects the opacity of the layer it is used on.
That is to say, if layer 1 was all blue and layer 2 was all green, using this brush tool on just one small spot on layer two would make that spot transparent, revealing the blue layer 1 underneath.
I would like to know - what is this tool called, and how may I access it?
Please do not confuse this with brush opacity, which is affecting the opacity of the image drawn by the brush. I am looking for a tool which affects the transparency of the layer it is draw onto. I am sure this feature exists, as my university tutor has used it, but I had forgotton how to access it.
Thank you in advance
Are you thinking of the eraser tool?
In the option bar, set the brush Mode to "Clear". You can also use the Brush option for the Eraser tool.