Iodine is used for visualization of compounds on TLC plats especially when they are showing up well. This method is particular useful when identifying unsaturated and aromatic compounds. These compounds have an affinity for iodine which turns the spots dark brown allowing them to be seen easily. Solution Iodine is used for visualization of compounds on TLC plats especially when they are showing up well. This method is particular useful when identifying unsaturated and aromatic compounds. These compounds have an affinity for iodine which turns the spots dark brown allowing them to be seen easily..