A standard cleaning solution for glass consists of 35 parts of a saturated solution of potassium dichromate mixed with 1000 parts of concentrated sulfuric acid. the acid should be poured slowly into the dichromate solution, while stirring. the solution is most is most effective when hot and should be used ataround 110. it should be red in color for best result. if the solutionn is muddy or greenish, it should be discarded. often glass is first washed with a soap solution andrinsed water before using the chomic acid solution finally ,the glass should be washed with warm distilled water and dried with hot, dust-free air. additional precautions must be taken with glass which to be coated with a metal film in vacuum. the threatment with chromic acid should be continueduntil a water film spreads uniformly over the glass surface. next dry the glass with wool. finally, polish with cotton wool and alchol until uniform water vapor film forms on the surface when breathed upon.