I exposed a complete board for 3 min and developed it for about 1min. This removes the mask coating on these pre treated boards in the areas exposed to the UV light and leaves the unexposed areas which were shielded by the artwork, these areas darken during the process. One of the most common developers is a solution of Sodium Hydroxide (Caustic Soda). I used simple Polypropylene food boxes to hold the liquids, they are cheap and withstand most chemicals. I wouldn't advise putting food in them afterwords, so keep them exclusively for this task.