After resting for 20 min the board was placed in a developing solution of Sodium Carbonate (Washing Soda).
It comes as a powder and is made up as 1g/100ml of water. The areas exposed to the light have hardened, the protected areas dissolve in a couple of minutes, a bit of help with a soft paint brush or tooth brush speeds up the process and makes sure any intricate parts are lifted off. When all the pads are clear the board is rinsed in clean water and dried.