How to test desized material (Starch based size):

To test the presense of sizing material i.e starch based sizing material in the fabric iodine test is conducted. In which the fabric is spotted or treated with  Iodine solution —Iodine dissolved in an aqueous solution of potassium iodide, which reacts with the starch and produce a bluish-purple-black colour. If there is no starch the colour may be brownish-yellowish.  In the below figure, it is explained that if the iodine solution is added in the solution ( which you want to know whether there is a starch or not) if there is a starch then you may get purple/bluish colur solution. If there is no starch the colour remain same. 

TEGEWA solution is also used for the identification of starch.  For making this solution potassium iodide 10 g of KI (100%) in 100 ml of water is added with 0.6358 g of iodine (100%) and shake this well to disslove iodine crystals. Then make it up to 800 ml using distilled water and finally make it up to 1000 ml with ethanol.